Cable Size Calculator Single & Three-Phase | IEC, BS 7671 & NEC
Choosing the correct cable size is one of the most important steps in any electrical installation. An undersized cable can overheat, create excessive voltage drop, and reduce the lifespan of connected equipment, while an oversized cable increases project costs unnecessarily. A Cable Size Calculator helps you select the correct conductor size based on electrical load, installation conditions, cable length, and applicable wiring standards.
This calculator is designed for electricians, electrical engineers, consultants, contractors, students, and even experienced DIY users who need fast and reliable cable sizing. Whether you are working on residential wiring, commercial buildings, industrial facilities, solar power systems, or motor installations, the tool simplifies the selection process.
Table of Contents
Table of Contents
Unlike many online tools that perform only a single calculation, this calculator checks both current carrying capacity and voltage drop in one process. It supports the three most widely used electrical standards—IEC, BS 7671, and NEC—making it suitable for projects across different countries and industries. Whether you need a single phase cable sizing calculator, a wire size calculator 3 phase, or a low voltage cable sizing solution, this tool provides practical results within seconds.
Cable Size Calculator (Single & 3-Phase) IEC, NEC & BS 7671
Cable Size Calculator
Current-carrying capacity, derating and voltage drop sizing for single & three-phase circuits
Circuit Details
Cable & Installation
How to Use
- Choose the design standard that applies to the installation: IEC 60364, BS 7671, or NEC.
- Select the phase configuration and enter the actual supply voltage.
- Enter the load either as a current in amps, or as a power in kW together with the power factor – the tool will work out the design current either way.
- Add a design margin if the circuit needs headroom for future load growth; leave it at none for an exact fit.
- Enter the one-way cable run length and the maximum voltage drop you are willing to accept.
- Pick the conductor material, installation method, ambient temperature, and how many other loaded circuits or cables run alongside this one.
- Press Calculate. The tool checks both the thermal (current-carrying) requirement and the voltage drop requirement, and reports the smallest cable size that satisfies both.
How the Sizing Works
The calculator first works out the actual current the cable has to carry, adding any design margin you selected. It then reduces the cable’s rated capacity to account for how hot the surroundings are and how many other loaded cables are bundled or grouped alongside it, since heat from neighboring cables and a warmer environment both reduce how much current a cable can safely carry before it overheats.
Once the required carrying capacity is known, the tool searches through standard cable sizes and picks the smallest one that comfortably meets that requirement. It then checks the voltage drop that this cable would produce over the length you entered – if the drop is higher than the limit you set, the tool steps up to the next larger cable size until the voltage drop is brought back within your chosen limit.
The final result tells you which of the two checks – heating or voltage drop – ended up deciding the cable size, since long cable runs with modest currents are often limited by voltage drop rather than heating, while short runs with heavy currents are usually limited by heating.
How This Calculator Works
The Cable Size Calculator begins by determining the expected electrical load based on the information you provide. Depending on the selected standard, it evaluates the operating current for either a single-phase or three-phase circuit. This design current forms the basis of the cable selection process.
The calculator then considers real installation conditions rather than relying on ideal laboratory values. Factors such as ambient temperature, cable grouping, installation method, insulation type, and conductor material all influence the cable’s ability to carry current safely. These adjustments work similarly to a cable derating calculator and help produce more accurate results.
Next, the tool compares the calculated current with the current carrying capacity of available cable sizes. Every conductor has a maximum continuous current rating, and the selected cable must safely carry the expected load without exceeding its temperature limits.
IEC vs BS 7671 vs NEC | What’s Different
Although all three standards aim to ensure safe electrical installations, they differ in conductor sizing methods, units, installation references, and acceptable design practices. Understanding these differences helps engineers and electricians select the appropriate cable for their region and project requirements.
| Feature | IEC Standards | BS 7671 (UK Wiring Regulations) | NEC (USA) |
|---|---|---|---|
| Conductor Size | mm² | mm² | AWG / kcmil |
| Primary Standard | IEC 60364 | BS 7671 (IET Wiring Regulations) | NFPA 70 (NEC) |
| Common Voltage Systems | 230/400 V | 230/400 V | 120/208 V, 120/240 V, 277/480 V |
| Insulation Temperature | 70°C, 90°C | 70°C, 90°C | 60°C, 75°C, 90°C |
| Reference Ambient Temperature | 30°C (Air) | 30°C (Air) | 30°C (86°F) |
| Voltage Drop Guidance | Typically 3–5% | 3% Lighting, 5% Other Loads | Informational Note recommends about 3% branch circuit and 5% overall feeder + branch circuit |
| Cable Identification | Cross-sectional Area | Cross-sectional Area | AWG/kcmil |
| Typical Applications | Europe, Asia, Middle East | United Kingdom | United States, Canada (with local code variations) |
Although the standards use different terminology and conductor sizes, they all follow the same engineering principle: the selected cable must safely carry the design current while keeping voltage drop within acceptable limits.
The Cable Size Calculator automatically applies the selected standard, making it easy to compare cable sizing across international projects without manually referring to multiple code books.
Copper Wire Size Chart in mm
Many electricians prefer using a copper wire size chart in mm because most IEC, BS 7671, and international electrical installations specify conductor sizes in square millimeters rather than AWG. Selecting the correct cable depends on current load, installation method, voltage drop, and ambient temperature.
| Copper Conductor Size (mm²) | Typical Current Range* | Common Applications |
|---|---|---|
| 1.5 mm² | 10–16 A | Lighting circuits |
| 2.5 mm² | 16–25 A | Socket outlets |
| 4 mm² | 25–32 A | Small appliances |
| 6 mm² | 32–40 A | Water heaters, AC units |
| 10 mm² | 45–63 A | Submains |
*Approximate values; always verify with applicable standards and installation conditions.
For complete conductor capacities, IEC ampacity tables, and practical sizing examples, refer to our detailed Copper Wire Size Chart in mm guide. It includes comprehensive cable selection tables for residential, commercial, and industrial installations.
Common Wire Sizes and Ratings
The table below provides approximate current ratings for commonly used copper conductors under favorable installation conditions. Actual ratings vary depending on installation method, ambient temperature, insulation type, grouping, and local electrical standards.
| Cable Size | Approx. Current Rating | Typical Applications |
|---|---|---|
| 1.5 mm² | 15–20 A | Lighting circuits |
| 2.5 mm² | 20–27 A | Socket outlets, small appliances |
| 4 mm² | 28–37 A | Water heaters, small AC units |
| 6 mm² | 36–47 A | Cookers, EV chargers, sub-circuits |
| 10 mm² | 50–65 A | Distribution boards, large appliances |
| 16 mm² | 65–85 A | Industrial feeders |
| 25 mm² | 85–115 A | Commercial distribution |
| 35 mm² | 110–140 A | Large motors |
| 50 mm² | 140–175 A | Main distribution feeders |
| 70 mm² | 180–230 A | Industrial LV networks |
| 95 mm² | 220–280 A | Heavy-duty feeders |
| 120 mm² | 260–330 A | Large commercial installations |
| 150 mm² | 300–370 A | Industrial substations |
| 185 mm² | 350–430 A | High-capacity distribution |
These values are intended as a quick reference only. Always use the calculator for final cable sizing because real installations require derating factors and voltage drop verification.
Wire Ampacity Table in mm² for Quick Cable Selection
A wire ampacity table in mm2 helps electricians and engineers quickly estimate the safe current-carrying capacity of common copper conductors before performing detailed voltage drop and derating calculations. Always verify the final cable size using applicable standards such as IEC 60364, BS 7671, or NEC, especially where ambient temperature, installation method, or grouping factors apply.
| Copper Cable Size (mm²) | Typical Ampacity (A) |
|---|---|
| 1.5 | 18–20 |
| 2.5 | 24–27 |
| 4 | 32–37 |
| 6 | 40–47 |
| 10 | 55–65 |
For a complete wire ampacity table in mm2, installation methods, correction factors, and standard ampacity charts, explore our detailed guide to ensure accurate cable selection for every application.
kW vs kVA Cable Sizing
Understanding kW vs kVA cable sizing helps select conductors based on both real power and apparent power. kW represents useful electrical power, while kVA includes the effect of power factor.
| Rating | Represents | Cable sizing use |
|---|---|---|
| kW | Real power | Load demand |
| kVA | Apparent power | Current calculation |
| Power factor | kW ÷ kVA | Converts kW to kVA |
For single-phase and three-phase systems, cable current should be calculated from kVA or kW with the applicable power factor before checking ampacity, voltage drop, and installation conditions. Use the kW vs kVA Cable Sizing guide for detailed calculations and practical examples.
Armoured Cable Size Calculator for Cable Selection
For underground, industrial, and outdoor installations, selecting the correct cable size requires considering load current, voltage drop, installation method, ambient temperature, and grouping factors. An Armoured Cable Size Calculator simplifies this process by helping determine an appropriate conductor size while accounting for these design conditions.
| Factor | Why It Matters |
|---|---|
| Load current | Determines required cable ampacity |
| Voltage drop | Ensures equipment receives adequate voltage |
| Installation method | Affects cable current-carrying capacity |
| Ambient temperature | May require derating |
For detailed calculations, cable selection tables, and practical examples, use the Armoured Cable Size Calculator guide to verify the recommended cable size before installation.
NEC Wire Size Chart for Quick Conductor Selection
A NEC Wire Size Chart helps electricians and engineers quickly match conductor sizes with their allowable ampacity based on the National Electrical Code (NEC). While your cable size calculator performs detailed calculations, the chart below provides a fast reference for common copper conductors. Always verify the final selection using NEC Article 310.16, insulation temperature rating, installation method, voltage drop, and ambient temperature correction factors.
| Copper Wire Size (AWG) | Typical Ampacity* |
|---|---|
| 14 AWG | 15 A |
| 12 AWG | 20 A |
| 10 AWG | 30 A |
| 8 AWG | 40–55 A |
| 6 AWG | 55–75 A |
*Ampacity varies by insulation type and installation conditions.
👉 Need a complete NEC Wire Size Chart with ampacity tables, conduit applications, and code references? Read our detailed guide for accurate NEC-compliant wire selection.
Motor Cable Size Calculator for Electric Motors
Selecting the correct motor cable size is essential for safe operation, voltage drop control, and compliance with IEC, BS 7671, and NEC standards. A dedicated Motor Cable Size Calculator considers motor full-load current (FLC), starting current, cable length, installation method, ambient temperature, and conductor material to recommend the appropriate cable size.
| Input Parameter | Example |
|---|---|
| Motor Power | 15 kW |
| Supply Voltage | 400 V |
| Phase | Three-Phase |
| Cable Length | 60 m |
| Conductor | Copper |
Unlike a general cable sizing tool, a Motor Cable Size Calculator is specifically designed for motor circuits, ensuring reliable starting performance and long-term efficiency.
For detailed calculations, worked examples, and motor-specific sizing rules, use our Motor Cable Size Calculator tool.
EV Charger Cable Size Calculator
Choosing the correct cable for an EV charger is essential for safety, voltage drop compliance, and future charging performance. An EV Charger Cable Size Calculator helps determine the appropriate conductor size based on charger current, supply voltage, installation method, cable length, and applicable standards such as IEC, BS 7671, and NEC. This reduces overheating risks and ensures the installation meets electrical code requirements.
| EV Charger Rating | Typical Current | Common Copper Cable* |
|---|---|---|
| 3.6 kW | 16 A | 2.5 mm² / 14 AWG |
| 7.4 kW | 32 A | 6 mm² / 10 AWG |
| 11 kW | 16 A (3-Phase) | 2.5–4 mm² |
| 22 kW | 32 A (3-Phase) | 6–10 mm² |
*Actual cable size depends on installation conditions and voltage drop.
For a precise calculation, use our dedicated EV Charger Cable Size Calculator, which provides code-compliant cable recommendations for residential and commercial EV charging installations.
Earth Cable Size Calculator
An accurate earthing cable size calculation ensures that the protective earth (PE) conductor can safely carry fault current until the protective device disconnects the circuit. Our Earth Cable Size Calculator follows IEC and BS 7671 principles by considering fault current, disconnection time, conductor material, and insulation type to recommend the minimum earth conductor size.
| Parameter | Typical Input |
|---|---|
| Fault Current | 500 A – 50 kA |
| Disconnection Time | 0.1–5 s |
| Conductor Material | Copper / Aluminum |
| Standard | IEC 60364, BS 7671 |
For detailed formulas, worked examples, and step-by-step earthing cable size calculation, use our dedicated Earth Cable Size Calculator to select a compliant protective conductor for residential, commercial, and industrial electrical installations.
Neutral Conductor Sizing Calculator
A Neutral Conductor Sizing Calculator helps determine the correct neutral cable size based on load current, phase configuration, harmonic content, and the applicable electrical code. If you are wondering how to size neutral conductor, the calculation depends on whether the system is single-phase or three-phase, balanced or unbalanced, and whether nonlinear loads require a full-sized neutral.
| System Type | Typical Neutral Size |
|---|---|
| Single-Phase | Same as phase conductor |
| Balanced Three-Phase | Reduced or as permitted by code |
| Nonlinear Loads | Full-size neutral recommended |
For a complete explanation of how to size neutral conductor, calculation examples, and code requirements under IEC, BS 7671, and NEC, use our dedicated Neutral Conductor Sizing Calculator. It covers practical sizing methods, harmonic considerations, and common installation scenarios.
Sub Panel Wire Size Calculator
A Sub Panel Wire Size Calculator helps determine the correct conductor size for safely feeding a residential or commercial subpanel. It considers feeder current, cable material, voltage drop, installation method, and the applicable electrical standard. If you’re installing a 100A subpanel, our detailed 100 amp wire size calculator explains conductor sizing, breaker selection, and voltage drop calculations with practical examples.
| Sub Panel Rating | Typical Copper Wire | Typical Aluminum Wire |
|---|---|---|
| 60A | 6 AWG | 4 AWG |
| 100A | 3 AWG | 1 AWG |
| 125A | 1 AWG | 1/0 AWG |
Need accurate feeder sizing? Use our 100 amp wire size calculator for complete NEC-compliant calculations, installation tips, and sizing charts before selecting your subpanel feeder cable.
MM to AWG & AWG to MM Wire Size Calculator
When working with IEC and NEC wiring standards, you may need to convert metric wire sizes (mm²) to American Wire Gauge (AWG). Our MM to AWG & AWG to MM Wire Size Calculator helps electricians, engineers, and DIY users quickly find the equivalent wire size for residential, commercial, and industrial installations. It is especially useful when selecting imported cables or comparing international specifications.
| Metric Size (mm²) | Approx. AWG |
|---|---|
| 1.5 mm² | 15 AWG |
| 2.5 mm² | 13 AWG |
| 4 mm² | 11 AWG |
| 6 mm² | 9 AWG |
| 10 mm² | 7 AWG |
Need accurate conversions? Try our dedicated MM to AWG & AWG to MM Wire Size Calculator for instant metric-to-AWG and AWG-to-metric wire size conversions before selecting the correct cable for your project.
Doncaster Cables Calculator for Fast Cable Selection
If you regularly work with UK electrical installations, a Doncaster Cables Calculator can help estimate the correct cable size based on current, installation method, voltage drop, and cable length. While our Cable Size Calculator supports IEC, BS 7671, and NEC sizing principles, a dedicated Doncaster cable sizing guide provides product-specific recommendations commonly used by UK electricians and contractors.
| Feature | Benefit |
|---|---|
| BS 7671-based sizing | Supports UK wiring practices |
| Voltage drop checks | Improves compliance and efficiency |
| Installation method input | More accurate cable selection |
| Quick current capacity lookup | Saves design time |
For UK-specific cable selection and practical examples, explore our detailed Doncaster Cables Calculator guide, which explains sizing methods, cable ratings, and installation considerations in greater depth.
Street Light Cable Size Calculation
Street light cable size calculation ensures safe voltage drop, reliable illumination, and long service life for outdoor lighting circuits. The correct cable depends on lamp wattage, supply voltage, installation distance, ambient temperature, and the number of fixtures connected to the same feeder. Selecting an undersized cable can reduce brightness and increase energy losses.
| Factor | Why It Matters |
|---|---|
| Total Lighting Load | Determines current demand |
| Cable Length | Affects voltage drop |
| Supply Voltage | Impacts cable selection |
| Installation Method | Influences current-carrying capacity |
If you’re designing landscape or outdoor lighting systems, try our garden lighting cable calculator for dedicated cable sizing, voltage drop calculations, and practical recommendations for residential and commercial installations. It provides a faster, more accurate solution for low-voltage and decorative lighting projects.
Understanding Cable Derating Factors
Cable manufacturers publish current ratings under standard test conditions. Real-world installations rarely match these conditions, so correction factors must be applied before selecting a conductor size. This process is commonly known as cable derating.
Ignoring derating factors can lead to excessive conductor temperatures, insulation damage, nuisance breaker trips, and reduced equipment life. That is why every professional cable sizing calculation includes derating before confirming the final conductor size. Know more about Cable Derating Factors here in our detailed guide.
Ambient Temperature
Cable ratings are normally based on a reference ambient temperature defined by the applicable standard. Higher surrounding temperatures reduce the cable’s ability to dissipate heat, lowering its safe current carrying capacity.
For example, cables installed on rooftops, inside electrical rooms, or near industrial furnaces operate in hotter environments than cables buried underground or installed in climate-controlled buildings. In these situations, a larger conductor may be required even if the electrical load remains unchanged.
The calculator automatically applies temperature correction factors where appropriate, helping users perform accurate low voltage cable sizing calculations.
Grouping / Bundling
When multiple cables are installed together in conduits, cable trays, trunking, or underground ducts, they generate heat collectively. Since each cable affects the cooling of neighboring cables, their individual current carrying capacities decrease.
This is why grouping factors are included in professional cable design calculation methods. A circuit that is perfectly safe when installed alone may require a larger conductor when grouped with several other circuits.
The integrated cable derating calculator accounts for these conditions to improve installation safety and compliance with international standards.
Installation Method
The way a cable is installed has a major impact on its current rating. Cables clipped directly to a wall generally dissipate heat more effectively than cables enclosed inside conduits, buried underground, or installed within insulated walls.
Different installation methods therefore have different ampacity ratings under IEC, BS 7671, and NEC requirements. Selecting the correct installation method ensures the calculator determines a realistic current carrying capacity rather than relying on theoretical values.
Considering installation conditions during cable calculation helps prevent overheating and improves long-term system reliability.
Voltage Drop Explained
Current carrying capacity is only one part of proper cable selection. The second equally important consideration is voltage drop.
As electricity flows through a conductor, a small portion of the supply voltage is lost due to the cable’s electrical resistance. The longer the cable run, the greater this voltage loss becomes.
For short circuits, voltage drop is often negligible. However, long cable runs supplying motors, pumps, EV chargers, agricultural equipment, HVAC systems, or remote buildings can experience significant voltage reduction even when the cable safely carries the required current.
Excessive voltage drop can lead to several problems, including:
- Reduced motor starting torque
- Increased motor heating
- Poor lighting performance
- Lower efficiency of electrical equipment
- Unexpected shutdown of sensitive electronics
- Reduced performance of EV chargers and renewable energy systems
A voltage drop calculator helps identify when conductor size should be increased to maintain acceptable voltage at the load. In many practical installations, voltage drop determines the final cable size rather than ampacity.
For example, a 40 A circuit supplying equipment located 150 meters away may thermally require only a 10 mm² cable. However, voltage drop calculations may indicate that a 16 mm² or 25 mm² conductor is necessary to remain within allowable limits.
This is why professional engineers always verify both current carrying capacity and voltage drop before finalizing any cable sizing calculation.
Modern electrical design standards recognize the importance of voltage regulation. Whether you are performing LV cable sizing for commercial buildings or designing industrial distribution systems, checking voltage drop ensures equipment receives sufficient voltage for reliable operation throughout its service life.
Related Tools & Guides
- DC Cable Size Calculator
- cable size for 7kw eV charger
- 30 kw motor cable size
- earth conductor size calculation
- hT cable size calculation
Frequently Asked Questions
How do I calculate cable size for a given load?
Start by determining the load current based on power, voltage, and power factor. Then consider cable length, installation method, ambient temperature, grouping, and allowable voltage drop. The Cable Size Calculator performs all these checks automatically to recommend an appropriate conductor size.
What size cable do I need for a 32 A or 63 A circuit?
There is no single answer because cable size depends on installation conditions. For many standard installations, a 32 A circuit often uses 4 mm² or 6 mm² cable, while a 63 A circuit commonly requires 10 mm² or 16 mm² cable. However, voltage drop, cable length, and derating may require larger conductors.
How does temperature affect cable size?
Higher ambient temperatures reduce a cable’s ability to dissipate heat, lowering its current carrying capacity. As temperature increases, larger cable sizes may be required to safely carry the same electrical load.
What’s the difference between IEC and NEC cable sizing?
IEC and BS 7671 use metric conductor sizes measured in square millimeters (mm²), whereas NEC uses American Wire Gauge (AWG) and kcmil. The ampacity tables, installation methods, and correction factors also differ between the standards.
How much voltage drop is acceptable in a cable run?
Most electrical installations aim to keep voltage drop within 3% for lighting circuits and around 5% for other power circuits, depending on the applicable electrical standard. Excessive voltage drop can reduce equipment performance and increase energy losses.
Disclaimer
This calculator is intended to assist with preliminary electrical design and educational purposes. Final conductor selection should always comply with the latest edition of IEC standards, BS 7671, NEC, manufacturer recommendations, project specifications, and local electrical regulations. A qualified electrical engineer or licensed electrician should verify all calculations before installation.
Get new guides in your feed. Follow Electrical Insights on LinkedIn for new electrical standards guides, calculators and design tips from Azad Circuit Hub.
CableSizeCalculator, #ElectricalCalculator, #CableSizing, #IECStandards, #BS7671, #NECCode, #ElectricalEngineering, #VoltageDrop, #ElectricalDesign, #PowerSystems
Cable Size Calculator | IEC, NEC & BS 7671 : AzadCircuitHub
Free cable size calculator for single and three-phase circuits. Covers IEC 60364, BS 7671 and NEC sizing with derating and voltage drop checks.
Price Currency: USD
Operating System: EngineeringApplication
Application Category: Utility
