Wire Size Calculator
Load amps
One-way distance (ft)
Source volts
Max drop %
Phase
Conductor material
Insulation temp rating
60°C = older TW · 75°C = THW/RHW (most common) · 90°C = THHN/XHHW. Lugs and breakers usually limit you to the 75°C column even with 90°C wire.
Use this wire
10 AWG
Driven by voltage drop over this distance.
Ampacity-required
14 AWG
20 A at 75°C
Voltage-drop-required (≤3%)
10 AWG
Stays under 3% over 100 ft
Voltage drop
4.97 V
Drop percent
2.07%
Wire ampacity
35 A
Run length
200 ft round-trip
Show full NEC ampacity table (Table 310.16)
| Size | cmil | Cu 60° | Cu 75° | Cu 90° | Al 60° | Al 75° | Al 90° |
|---|---|---|---|---|---|---|---|
| 14 AWG | 4,110 | 15 | 20 | 25 | — | — | — |
| 12 AWG | 6,530 | 20 | 25 | 30 | 15 | 20 | 25 |
| 10 AWG | 10,380 | 30 | 35 | 40 | 25 | 30 | 35 |
| 8 AWG | 16,510 | 40 | 50 | 55 | 35 | 40 | 45 |
| 6 AWG | 26,240 | 55 | 65 | 75 | 40 | 50 | 55 |
| 4 AWG | 41,740 | 70 | 85 | 95 | 55 | 65 | 75 |
| 3 AWG | 52,620 | 85 | 100 | 115 | 65 | 75 | 85 |
| 2 AWG | 66,360 | 95 | 115 | 130 | 75 | 90 | 100 |
| 1 AWG | 83,690 | 110 | 130 | 145 | 85 | 100 | 115 |
| 1/0 | 105,600 | 125 | 150 | 170 | 100 | 120 | 135 |
| 2/0 | 133,100 | 145 | 175 | 195 | 115 | 135 | 150 |
| 3/0 | 167,800 | 165 | 200 | 225 | 130 | 155 | 175 |
| 4/0 | 211,600 | 195 | 230 | 260 | 150 | 180 | 205 |
| 250 kcmil | 250,000 | 215 | 255 | 290 | 170 | 205 | 230 |
| 300 kcmil | 300,000 | 240 | 285 | 320 | 195 | 230 | 260 |
| 350 kcmil | 350,000 | 260 | 310 | 350 | 210 | 250 | 280 |
| 400 kcmil | 400,000 | 280 | 335 | 380 | 225 | 270 | 305 |
| 500 kcmil | 500,000 | 320 | 380 | 430 | 260 | 310 | 350 |
| 600 kcmil | 600,000 | 350 | 420 | 475 | 285 | 340 | 385 |
NEC reference values. Table 310.16 ampacities for not more than three current-carrying conductors in raceway. Voltage-drop math uses K = 12.9 (Cu) or 21.2 (Al). Always confirm against your local code, conduit fill, bundling derate, and terminal temp limits — this tool is a starting point, not a permit.
Pairs well with
WS
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