Wire, conduit and fastener reference for the trades
Electrical charts and calculators that show their work
Voltage drop, conduit fill, ampacity, wire gauge and trade size references. Every number is calculated from a published formula or standard dimension, with the method and assumptions printed on the page.
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Voltage Drop Calculator
Enter load, length and conductor. Get percent drop, end voltage and the minimum size that stays under 3%.
Conduit Fill Calculator
Fill percentage against the 53 / 31 / 40 percent rule for EMT, IMC, RMC and PVC, plus the smallest legal raceway.
Ampacity Chart
Estimated allowable ampacity by size, material and insulation rating, with ambient and bundling derating applied.
Copper wire quick reference
| Size (AWG) | Circular mils | Diameter (in) | Est. amps @ 75 °C | Ω / 1000 ft | Detail |
|---|---|---|---|---|---|
| 14 | 4,107 | 0.0641 | 18 A | 2.525 | 14 AWG specs |
| 12 | 6,530 | 0.0808 | 24 A | 1.588 | 12 AWG specs |
| 10 | 10,383 | 0.1019 | 32 A | 0.999 | 10 AWG specs |
| 8 | 16,510 | 0.1285 | 44 A | 0.628 | 8 AWG specs |
| 6 | 26,251 | 0.1620 | 59 A | 0.395 | 6 AWG specs |
| 4 | 41,741 | 0.2043 | 80 A | 0.248 | 4 AWG specs |
| 2 | 66,371 | 0.2576 | 108 A | 0.156 | 2 AWG specs |
| 1/0 | 105,535 | 0.3249 | 146 A | 0.098 | 1/0 AWG specs |
| 2/0 | 133,077 | 0.3648 | 170 A | 0.078 | 2/0 AWG specs |
| 4/0 | 211,600 | 0.4600 | 230 A | 0.049 | 4/0 AWG specs |
Source & method: Diameter from ASTM B258 AWG geometry, d(mils) = 5 × 92^((36 − n) / 39). Resistance from R = ρ × 1000 / cmil with ρ = 10.371 Ω·cmil/ft for annealed copper at 20 °C. Ampacity from the power-law model documented on the methodology page.