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Wire Size Calculator – AWG & mm²
Enter your load current, voltage, phase, and distance. The calculator selects the smallest conductor that meets both ampacity and voltage drop (≤3%) per NEC 310.16 and IEEE 141.
Enter Your Circuit Parameters
All inputs are required for an accurate recommendation.
Recommended Conductor
Calculation Results
Minimum Wire Size
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Enter parameters and click Calculate
Ampacity Basis
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Voltage Drop
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Actual Current Capacity
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Recommended Breaker
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Installation Note
Adjust inputs above to size your circuit.
Based on NEC 310.16 (75°C terminations) and voltage drop per IEEE 141. Always consult local codes and a qualified electrician.
Reference Data
Comprehensive Reference Tables
Complete wire sizing data including NEC 310.16 ampacity, breaker pairings, voltage drop distances, and AWG‑to‑mm² conversion. Use these tables for quick look‑up or as a backup to the calculator.
Table A – NEC 310.16 Ampacity
Ampacity is the maximum current a conductor can carry continuously without exceeding its insulation temperature rating. In North America the governing values come from NEC Table 310.16. Ampacity depends on the conductor's temperature rating – the higher the rating, the more current the same wire can carry. The table below shows the 75°C column, the default for most breaker and equipment terminations per NEC 110.14(C). If you are not sure, size to the 75°C column and you will be safe in the vast majority of installations.
| AWG / kcmil | Ampacity (75°C) | AWG / kcmil | Ampacity (75°C) |
|---|---|---|---|
| 14 AWG | 20 A | 1/0 AWG | 150 A |
| 12 AWG | 25 A | 2/0 AWG | 175 A |
| 10 AWG | 35 A | 3/0 AWG | 200 A |
| 8 AWG | 50 A | 4/0 AWG | 230 A |
| 6 AWG | 65 A | 250 kcmil | 255 A |
| 4 AWG | 85 A | 350 kcmil | 310 A |
| 3 AWG | 100 A | 500 kcmil | 380 A |
| 2 AWG | 115 A | 750 kcmil | 475 A |
| 1 AWG | 130 A | 1000 kcmil | 545 A |
Which column should you use? The 60°C column applies to NM‑B (Romex) and UF‑B, most residential indoor wiring. The 75°C column is the default for anything landing on circuit‑breaker terminals. The 90°C column is a starting point for derating calculations, but the final rating is usually limited by the 75°C terminal. When in doubt, use the 75°C column.
Table B – Common Circuit Breaker to Wire Size
For quick everyday decisions, most people don't work backwards from ampacity – they start from the circuit breaker. This chart pairs standard breaker sizes with the correct copper conductor. It is the fastest way to answer "what size wire for X amps?"
| Breaker | Copper Wire | Typical Application |
|---|---|---|
| 15 A | 14 AWG | Lighting, receptacles |
| 20 A | 12 AWG | Kitchen, bathroom, garage |
| 30 A | 10 AWG | Dryer, water heater |
| 40 A | 8 AWG | Range, EV charger |
| 50 A | 6 AWG | Hot tub, welder |
| 60 A | 6 AWG | Subpanel feeder |
| 70 A | 4 AWG | Large heater |
| 80 A | 3 AWG | Commercial feeder |
| 100 A | 2 AWG | 100A subpanel |
| 125 A | 1 AWG | Service entrance |
| 150 A | 1/0 AWG | Service entrance |
| 175 A | 2/0 AWG | Feeder |
| 200 A | 3/0 AWG | 200A service |
| 225 A | 4/0 AWG | Large feeder |
| 250 A | 250 kcmil | Service entrance |
| 300 A | 350 kcmil | Industrial feeder |
| 400 A | 500 kcmil | Industrial main |
NEC 240.4(D) small conductor rule: 14 AWG tops out at a 15 A breaker, 12 AWG at 20 A, and 10 AWG at 30 A, regardless of ampacity table values. The chart above already respects this rule.
Table C – Max Distance for 3% Voltage Drop (240V, Copper)
Ampacity tells you the wire won't overheat. Voltage drop tells you the equipment at the end of a long run will still work. The NEC recommends no more than 3% voltage drop on a branch circuit and 5% total (feeder + branch). For a given gauge, the acceptable distance shrinks at lower voltages. At 120V, halve these distances – a run that holds 3% at 76 feet on 240V needs 14 AWG only up to roughly 38 feet at 120V.
| Breaker | Wire Size | Max Distance (ft) | Equivalent at 120V |
|---|---|---|---|
| 15 A | 14 AWG | 76 | 38 |
| 20 A | 12 AWG | 91 | 45 |
| 30 A | 10 AWG | 97 | 48 |
| 40 A | 8 AWG | 115 | 57 |
| 50 A | 6 AWG | 146 | 73 |
| 60 A | 4 AWG | 194 | 97 |
| 100 A | 3 AWG | 147 | 73 |
Rule of thumb: For runs over roughly 100 feet, go up one wire size for every additional 100 feet of distance at 120V, and about half that penalty at 240V. The safest approach is to size for the larger of the ampacity result and the voltage‑drop result.
Table D – AWG to mm² Conversion
If you work in a market that uses metric cable (IEC 60228 / BS 7671 wiring regulations), or you are buying imported equipment with metric conductors, you need this pairing. Most electrical wire size charts online are AWG‑only or mm²‑only; this table gives you both so you can read either system confidently.
| AWG / kcmil | mm² (approx) | AWG / kcmil | mm² (approx) |
|---|---|---|---|
| 18 AWG | 0.8 | 2 AWG | 33.6 |
| 16 AWG | 1.3 | 1 AWG | 42.4 |
| 14 AWG | 2.1 | 1/0 AWG | 53.5 |
| 12 AWG | 3.3 | 2/0 AWG | 67.4 |
| 10 AWG | 5.3 | 3/0 AWG | 85.0 |
| 8 AWG | 8.4 | 4/0 AWG | 107.2 |
| 6 AWG | 13.3 | 250 kcmil | 127 |
| 4 AWG | 21.2 | 350 kcmil | 177 |
| 3 AWG | 26.7 | 500 kcmil | 253 |
Important: When replacing an imported cable, match the nearest mm² size that meets both the ampacity and voltage‑drop requirements – do not simply convert the number, because standards round differently. Always verify with the manufacturer's data sheet.
Special Applications
DC, Generator & Material‑Specific Tables
Quick reference for low‑voltage DC systems, generator output cables, and copper‑vs‑aluminium sizing. Use these tables when the general charts don't cover your specific equipment.
12V / 24V / 48V DC Inverter Cable
| Inverter Power | 12V (0–3 ft) | 12V (3–6 ft) | 24V (0–6 ft) | 48V (0–10 ft) |
|---|---|---|---|---|
| 600 W | 8 AWG | 6 AWG | 10 AWG | 12 AWG |
| 1000 W | 4 AWG | 2 AWG | 8 AWG | 10 AWG |
| 1500 W | 1/0 AWG | 2/0 AWG | 6 AWG | 8 AWG |
| 2000 W | 2/0 AWG | 3/0 AWG | 4 AWG | 6 AWG |
| 3000 W | 4/0 AWG | 4/0 AWG | 1/0 AWG | 4 AWG |
DC sizing note: Voltage drop is the dominant factor. For longer runs, go up one to two sizes. Always fuse within 18 inches of the battery.
Generator kVA → Cable Size (mm²)
| Generator (kVA) | Full‑Load Amps (415V, 3‑phase) | Cu Cable (mm²) | Al Cable (mm²) |
|---|---|---|---|
| 15 kVA | 21 A | 4 | 6 |
| 25 kVA | 35 A | 6 | 10 |
| 40 kVA | 56 A | 10 | 16 |
| 62.5 kVA | 87 A | 16 | 25 |
| 100 kVA | 139 A | 35 | 50 |
| 160 kVA | 223 A | 70 | 95 |
| 200 kVA | 279 A | 95 | 120 |
| 250 kVA | 348 A | 120 | 185 |
| 320 kVA | 445 A | 150 | 240 |
| 400 kVA | 556 A | 240 | 300 |
Based on 75°C, 3% drop at standard lengths. For runs over 50 m, add one size. Always verify with the generator data sheet and local code.
Copper vs Aluminium – Size Comparison
| Load (Amps) | Copper (AWG) | Aluminium (AWG) | Al Cu‑equivalent |
|---|---|---|---|
| 20 A | 12 | 10 | +1 size |
| 30 A | 10 | 8 | +1 size |
| 50 A | 6 | 4 | +1 size |
| 70 A | 4 | 2 | +1 size |
| 100 A | 2 | 1/0 | +2 sizes |
| 125 A | 1 | 2/0 | +2 sizes |
| 150 A | 1/0 | 3/0 | +2 sizes |
| 200 A | 3/0 | 250 kcmil | +2 sizes |
| 225 A | 4/0 | 300 kcmil | +2 sizes |
| 250 A | 250 kcmil | 350 kcmil | +1 size |
Aluminium requires anti‑oxidant compound and AL‑rated lugs. For long runs, aluminium can be cost‑effective, but copper is the safer default for critical circuits.
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Frequently Ask Questions
Q: What size wire do I need for 100 amps?
A: For a 100-amp circuit, use 2 AWG copper (or 1/0 AWG aluminum) at 75°C. At 100 amps over a long run (beyond about 147 feet at 240V), you will need to upsize to 1 AWG or larger to hold voltage drop within 3%.
Q: What size wire for a 200 amp service?
A: A 200-amp residential service typically uses 3/0 AWG copper or 250 kcmil aluminum, sized to the 75°C column and terminated on 200A-rated lugs. Confirm the exact size against your local code and the actual run length.
Q: How many amps can 12-gauge wire handle?
A: 12 AWG copper carries 20A at 60°C, 25A at 75°C, and 30A at 90°C per NEC 310.16. In practice, it is protected by a 20A breaker (NEC 240.4(D)), which is what almost every residential circuit uses.
Q: How far can you run 10-gauge wire before voltage drop?
A: At 240V with a 30A load, 10 AWG holds 3% voltage drop to about 97 feet. At 120V, halve that to about 48 feet. Beyond those distances, step up to 8 AWG.
Q: What size wire for a 50 amp circuit at 100 feet?
A: 6 AWG copper meets the ampacity requirement, but at 100 feet on a 240V circuit the voltage drop approaches the 3% limit; for a 120V circuit, use 4 AWG. When in doubt, size by distance, not just amps.
Q: Is 6 AWG wire big enough for 50 amps?
A: Yes. 6 AWG copper is rated 55A at 60°C and 65A at 75°C, so a 50A circuit is well within range for short runs. On long runs, check voltage drop and step up to 4 AWG if needed.
Q: What size wire do I need for a 220V / 240V circuit?
A: The voltage does not change the ampacity; only the distance you can run before voltage drop. A 30A, 240V circuit uses 10 AWG; a 50A, 240V circuit uses 6 AWG. At 240V you can run roughly twice as far as at 120V for the same gauge.
Q: What size wire for a 60 amp subpanel?
A: 6 AWG copper is rated for 65A at 75°C, which covers a 60A subpanel for short runs. For runs over roughly 194 feet at 240V, step up to 4 AWG to keep voltage drop within 3%.