Cable Size & Wire Gauge Calculator
Screen standard mm² and approximate AWG / wire gauge from design amps or kW (1φ/3φ, Cu / Al)—including DC, 12 V, battery, inverter, and VFD feeder screening—then verify derating, voltage drop, and protection on real tables.
Quick presets (wire gauge / DC / VFD)
Load a scenario, then refine amps or run length for the NEC voltage-drop handoff.
Calculator
Quick: design amps or kW + PF → line current → AWG screen + mm². Advanced: Ca/Cg derating and run length (m or ft) for NEC/IEC voltage-drop handoff.
Inputs (amps or kW, voltage, phase, material)
Quick feeder screening for industrial and commercial panels—results show an NEC-style AWG screen plus the IEC mm² ladder. After you pick a candidate, validate long runs with the NEC voltage drop or IEC voltage drop calculator.
Line current is calculated and shown in the results; the amps field updates automatically.
Advanced — derating & run length
Optional. Derating multiplies into screening current as It = Ib ÷ (Ca × Cg). Factors are illustrative; use your project code tables for final design.
Tip: Switch to From kW for a one-step 3-phase cable size from load power, or keep amps for direct screening.
About this calculator
Turn design amps or kW + PF into an NEC-style AWG screen plus the next standard mm² from a fixed IEC ladder—optionally apply illustrative Ca/Cg derating—before you lock BOMs or panel schedules. For the same protection workflow lane, use the protection calculators hub; for long feeders after sizing, use the NEC / AWG voltage drop calculator. Deeper narrative: voltage drop calculation and Motor Starting Current & Protection.
Prefer From kW for a one-step 3-phase cable size (Ib = P ÷ (√3 × V × PF)), or keep From design amps when you already have line current from 3-phase power / kVA to amps.
Calculation Results
Calculation Results
System: Three Phase, 400 V, Copper conductor
Wire gauge screen (NEC 75 °C–style): 6 AWG for ≈63 A Cu (confirm Table 310.16 + conditions)
Recommended Cable Size (IEC ladder): 16 mm²
Enter one-way run length under Advanced to prefill the NEC voltage drop or IEC voltage drop calculator.
IEC mm² ladder plus NEC-style AWG ampacity screen for planning. Optional Advanced Ca/Cg factors inflate screening current only; harmonics, demand diversity, and short-circuit limits are not modeled here.
Engineering disclaimer
This calculator provides cable screening estimates only. For final electrical system design, conductor selection, and compliance with local electrical codes, consult a licensed electrical engineer or certified professional. Actual requirements may vary based on installation method, ambient conditions, harmonics, and specific application requirements.
Common screening ladder — quick reference (Cu)
Illustrative pairs from the same IEC 60228-style step table used in the calculator (typical copper screening at moderate conditions). Enter your design current above; verify tabulated ampacity with manufacturer data after derating and voltage drop. AWG column is approximate for NEC cross-check only.
| Design current (A) | Next standard Cu mm² (screening) | Approx. AWG (NEC ref.) |
|---|---|---|
| 15 | 1.5 | 16 AWG |
| 20 | 2.5 | 14 AWG |
| 30 | 4 | 12 AWG |
| 40 | 6 | 10 AWG |
| 55 | 10 | 8 AWG |
| 75 | 16 | 6 AWG |
| 100 | 25 | 4 AWG |
| 125 | 35 | 2 AWG |
| 150 | 50 | 1 AWG |
| 200 | 70 | 2/0 AWG |
Ambient & grouping derating — screening reference
Illustrative correction factors—always use your project wiring code tables (NEC 310.15, IEC 60364-5-52, BS 7671 Appendix 4, etc.). This calculator outputs underrated mm² from design current only; multiply tabulated ampacity by these factors, or divide required load current by the combined factor to find minimum allowable ampacity.
Example ambient correction (75 °C copper, NEC-style illustration)
| Ambient (°C) | Correction factor |
|---|---|
| 21–25 | 1.00 |
| 31–35 | 0.94 |
| 41–45 | 0.88 |
| 51–55 | 0.82 |
Example bundling / grouping adjustment (NEC-style illustration)
| Current-carrying conductors in raceway/cable | Adjustment factor |
|---|---|
| 1–3 | 1.00 |
| 4–6 | 0.80 |
| 7–9 | 0.70 |
| 10–20 | 0.50 |
Combined derating example: Design current 63 A → screening ladder suggests 16 mm² Cu. If ambient 41–45 °C (factor 0.88) and 4–6 grouped conductors (factor 0.80), required tabulated ampacity ≥ 63 ÷ (0.88 × 0.80) ≈ 89 A → upsize to the next ladder step (often 25 mm² for Cu screening). Then check voltage drop and OCPD coordination.
OCPD type (fuse vs breaker): see Fuse vs Breaker Sizing Guide.
Cable sizing method & formula context
- I
- Design load current in amperes (RMS, steady-state basis you are sizing for).
- V
- Nominal system voltage in volts (line-to-neutral for single-phase, line-to-line for three-phase).
- mm²
- Conductor cross-sectional area per IEC 60228 standard sizes; output here is always an integer mm² step.
- Ampacity
- Tabulated allowable current for a conductor under stated conditions; must be derated for grouping, ambient, and installation method.
- PF (cos φ)
- Power factor when converting from kW to kVA before finding line current.
Obtain design current: single-phase I = kVA × 1000 ÷ V; balanced three-phase I = kVA × 1000 ÷ (√3 × V) with √3 ≈ 1.732. From kW: kVA = kW ÷ PF, then use the line-current formula for your phase.
Screening rule (this tool): pick the smallest standard mm² whose ladder step current is ≥ I (or ≥ It when Advanced Ca/Cg are set, with It = Ib ÷ (Ca × Cg)). This is not a substitute for manufacturer ampacity tables, harmonics, insulation temperature rating (for example XLPE 90 °C), or short-circuit/adiabatic withstand proofs.
Solar / PV DC strings: Use paralleled string current from the series-parallel calculator (often Isc × N_parallel), then apply project safety factor (commonly ~1.25× on Isc for continuous DC) as the design amps here. Method: how to size solar DC cable. Confirm with MPPT sizing and the Solar calculator hub—this page absorbs solar DC cable screening; not a separate PV-cable-only tool.
12 V / 24 V / 48 V battery & inverter DC: Enter continuous DC amps (or use Quick presets), set Phase to DC (2-wire) and voltage to 12/24/48. Ampacity screen gives AWG + mm²; then set one-way length (ft) under Advanced and open NEC voltage drop—low-voltage DC % loss climbs fast on long runs.
VFD / motor feeder screening: Use motor FLA × code factor (often 125%) as design amps, or the VFD preset (~63 A). This screens ampacity only—drive cable length, PWM reflections, and shield rules need manufacturer guidance after the ampacity + voltage-drop check.
Worked example (with numbers)
Given: 37 kW production load, PF 0.85, 400 V three-phase copper feeder.
Step 1 — kVA: 37 ÷ 0.85 ≈ 43.5 kVA.
Step 2 — line current: 43.5 × 1000 ÷ (1.732 × 400) ≈ 62.8 A → use 63 A design current.
Step 3 — screening mm²: 63 A maps to the next ladder step → 16 mm² Cu (integer output).
Step 4 — verify: apply grouping/ambient derating on project tables; check route length with the voltage drop calculator; confirm OCPD and fault current withstand with the breaker size calculator.
Use the suggested mm² as an early BOM or panel schedule checkpoint, then validate against detailed manufacturer tables including ambient, installation method, and voltage drop along the route.
Next step after screening: combine your candidate size with breaker frames and source ratings using the breaker size calculator, transformer size calculator, and generator size calculator, then confirm against IEC/NEC tables. Browse the protection calculators hub for the full lane.
Common standards designers cross-check
Cable sizing in practice is read against regional wiring rules and tabulated ampacity—for example IEC 60364, NEC ampacity tables (e.g. Table 310.16 / 310.15), BS 7671, or AS/NZS 3008—plus manufacturer datasheets. This page’s calculator is IEC 60228 mm²-first for early screening; US projects must still pick conductors from the adopted NEC ampacity table for insulation and installation method.
NEC / AWG cross-check for US projects
After you have a candidate mm², map to approximate AWG/kcmil and confirm allowable amps under NEC (temperature rating, ambient, bundling). The calculator does not output AWG directly—use the table below and the AWG column in the quick reference.
| Screening mm² (Cu) | Approx. AWG | Typical NEC continuous screen (75 °C Cu, illustration) |
|---|---|---|
| 6 | 10 AWG | ~30 A branch / small feeder |
| 10 | 8 AWG | ~40–50 A |
| 16 | 6 AWG | ~55–65 A |
| 25 | 4 AWG | ~70–85 A |
| 35 | 2 AWG | ~95–115 A |
| 50 | 1 AWG | ~110–130 A |
| 70 | 2/0 AWG | ~145–175 A |
Quick PAA: ~100 A continuous at 480 V three-phase often lands near 3 AWG Cu (75 °C) or 1 AWG Al on many NEC Table 310.16 readings—always apply ambient/bundling corrections and match OCPD with the breaker size calculator.
3-phase motor cable sizing (FLA screen)
Motors: take nameplate or NEC Table 430.250 FLA, apply continuous/branch factors from your code (often 125% of FLA for conductors), enter that design amps above for mm² screening, then map to AWG. Example: ~50 HP @ 460 V ≈ 65 A FLA → 65 × 1.25 ≈ 81 A → screening ladder often ~25 mm² / 4 AWG Cu before voltage drop and starting voltage dip—see motor starting & protection.
Last updated: 2026-07-29. mm² screening + AWG illustration only—not a reprint of NEC Table 310.16 or IEC 60364-5-52.
References
- NFPA 70 (NEC) — ampacity & wiring methods
- IEC TC 64 / IEC 60364 wiring overview
- Engineering Toolbox — AWG wire gauges
Installation method, grouping & fault current
Real ampacity depends on how the run is installed—for example in conduit, on cable tray, buried, or in free air—together with grouping/bundling and ambient temperature derating. Use Advanced Ca/Cg for a quick upsized screen; still confirm final ampacity on your IEC/NEC project tables.
Fault current & protection: available fault current, device let-through, and adiabatic thermal limits can require a larger conductor than steady-state ampacity. Size OCPD and check short-circuit withstand after screening—see the breaker size calculator and motor starting & protection guide for coordination context.
More context: Voltage drop calculation · kW to kVA Formula Explained · 3-Phase Power Calculator · When to Use kVA Instead of kW
3-phase cable size chart (kW → A → mm² / AWG)
Screening look-up at PF 0.85 copper, underrated (Ca = Cg = 1). Line current Ib = P ÷ (√3 × V × PF). AWG is an approximate NEC cross-check only. Enter the same kW in the calculator (From kW) or apply Advanced derating when ambient/grouping apply.
| Load (kW) | Ib @ 400 V (A) | mm² / AWG @ 400 V | Ib @ 480 V (A) | mm² / AWG @ 480 V |
|---|---|---|---|---|
| 15 | 25.5 | 4 / 12 AWG | 21.2 | 4 / 12 AWG |
| 22 | 37.4 | 6 / 10 AWG | 31.1 | 6 / 10 AWG |
| 30 | 51.0 | 10 / 8 AWG | 42.5 | 10 / 8 AWG |
| 37 | 62.8 | 16 / 6 AWG | 52.4 | 10 / 8 AWG |
| 45 | 76.5 | 25 / 4 AWG | 63.7 | 16 / 6 AWG |
| 55 | 93.5 | 25 / 4 AWG | 77.8 | 25 / 4 AWG |
| 75 | 127.4 | 35 / 2 AWG | 106.2 | 35 / 2 AWG |
| 100 | 169.9 | 50 / 1 AWG | 141.6 | 50 / 1 AWG |
After screening, check long feeders on the voltage drop calculator and OCPD on the breaker size calculator.
Frequently Asked Questions
How do I size solar / PV DC cable?
Compute array current from module Isc × parallel strings (see series-parallel), apply your code’s continuous-current factor (often 1.25× on Isc), enter that design amps here for mm² screening, then check DC voltage drop on long runs. Start from the Solar calculator workflow—no separate solar-DC-only cable page.
How do I size 12 V battery or inverter DC cable?
Enter continuous DC amps (or click the 12 V battery / 48 V inverter preset), set Phase to DC (2-wire) and voltage to 12/24/48. Read the NEC-style AWG screen and IEC mm², enter one-way length in feet under Advanced, then check 12 V / DC voltage drop—percent loss is much higher than on 120 V AC for the same gauge.
Is this a wire gauge length calculator?
Ampacity (AWG/mm²) comes from design current; length is entered under Advanced to prefill the voltage-drop step. For “what gauge at this length?”, screen AWG here, then open NEC voltage drop with your feet and AWG to see % drop—or use the % drop table for a quick 20 A look-up.
Is this a wire gauge calculator / wire size calculator?
Yes. Enter design amps (or kW) to screen mm², then use the AWG/NEC cross-check for approximate wire gauge. The same tool covers 3-phase cable size, DC / 12 V / battery / inverter cable screening, and VFD feeder ampacity—then verify long runs on the voltage drop calculator.
What is a cable size calculator?
A cable size calculator screens IEC-style mm² from design amps and conductor material (Cu/Al). Example: 32 A copper → 6 mm² on the screening ladder—then apply derating and check voltage drop on long runs.
How do I calculate 3 phase cable size?
To calculate 3 phase cable size, enter From kW with PF and voltage (Ib = P ÷ (√3 × V × cos φ)), or enter design amps directly. Then screen the next standard mm² from this calculator’s IEC-style ladder, optionally apply Advanced Ca/Cg derating, and verify voltage drop on the actual run length.
How do bundled cables affect ampacity?
Grouped conductors reduce heat dissipation, so tabulated ampacity must be multiplied by a grouping derating factor from IEC 60364 or NEC tables. Use Advanced → Grouping correction Cg for a quick upsized screen (It = Ib ÷ (Ca × Cg)), then confirm on your project tables.
What ambient temperature derating should I apply?
Use the correction factor from your wiring code for the conductor insulation rating (for example 70 °C or 90 °C PVC/XLPE) and the expected ambient—or pick an illustrative Ca under Advanced. High ambient or enclosed trays often push you one mm² step—or more—above a current-only screening value.
When does fault current require a larger conductor?
Short-circuit thermal limits (adiabatic withstand) can force a larger cross-section than steady-state ampacity. Check available fault current, protection device let-through, and manufacturer k²S² limits—use the breaker size calculator and project fault studies after screening mm² here.
Can you provide a cable sizing example with numbers?
Given: 37 kW, PF 0.85, 400 V three-phase → kVA ≈ 43.5, line current I ≈ 63 A. Screening ladder → 16 mm² Cu. Then verify grouping derating and route voltage drop before locking the BOM.
How does mm² relate to AWG for NEC projects?
IEC 60228 uses metric mm²; NEC projects often specify AWG/kcmil. Approximate cross-checks: 6 mm² ≈ 10 AWG, 16 mm² ≈ 6 AWG, 25 mm² ≈ 4 AWG, 70 mm² ≈ 2/0 AWG—see the NEC / AWG cross-check table. Always confirm against NEC Table 310.16 (or your adopted edition) for insulation and installation method.
What size cable for 100 A at 480 V three-phase?
As a screening illustration, ~100 A continuous at 480 V 3-phase often lands near 3 AWG Cu (75 °C) or 1 AWG Al on many NEC ampacity readings—or ~35 mm² on this page’s IEC-style ladder before derating. Apply ambient/bundling corrections and match OCPD; use the calculator with 100 A design current.
How do I size cable for a 3-phase motor?
Use motor FLA (nameplate or NEC 430.250), apply your code’s conductor factor (often 125% of FLA), enter that amps above for mm², then map to AWG. Example: ~50 HP @ 460 V ≈ 65 A FLA → ~81 A → often ~25 mm² / 4 AWG Cu before voltage-drop checks. See motor cable sizing.
How do harmonics affect cable sizing?
Non-linear loads add harmonic current that increases conductor heating and neutral loading. Derating or upsizing may be required beyond a fundamental-frequency ampacity check—this page assumes steady-state RMS design current only.
What is the difference between copper and aluminum cables?
Copper has higher conductivity, so it carries more current for the same cross-section and is more compact, but more expensive. Aluminum is lighter and cheaper but often requires a larger cross-section and special terminations.
How does voltage drop affect cable sizing?
Long runs at high current can cause significant voltage drop. In many standards you must keep voltage drop below a specified percentage, which may require a larger cable than indicated by current capacity alone—use the voltage drop calculator after screening.
What standards do engineers cross-check for cable sizing?
Designers cross-check IEC 60364, NEC ampacity chapters, BS 7671, or AS/NZS 3008 plus manufacturer data for insulation temperature rating. This tool does not replace those tables or statutory compliance.
Does the calculator change results by installation method (conduit, tray, buried)?
Optionally. Use Advanced Ca (ambient) and Cg (grouping) to inflate the screening current. Real ampacity still depends on installation method (conduit, cable tray, buried, or free air); confirm correction factors on your project tables after you have a candidate mm².
Is this calculator suitable for final design?
No. It is intended for quick checks and concept design. Final cable selection must follow detailed tables from standards and manufacturers, and should be validated by a qualified electrical engineer.