Wire Voltage Drop Calculator
Calculate the voltage lost in a cable and the heat it produces from the wire size (AWG or mm²), length and current.
Formula and cautions
R = ρ·L / A and ΔV = I·R. Current flows out on one wire and back on the other, so the round-trip length is normally used. At low DC voltages such as 12 V or 5 V a small drop is a large share of the supply, which is why LED strips and motors often misbehave on long runs. This tool covers voltage drop only. How much current a wire can safely carry depends on its insulation and installation, so check the cable's ampacity rating separately.
Worked example: 12 V LED strip, 3 A, 5 m away
- AWG 18: 10 m round trip is 209 mΩ → drop 628 mV (5.2%)
- AWG 16: 10 m round trip is 132 mΩ → drop 395 mV (3.3%)
- AWG 14: 10 m round trip is 82.8 mΩ → drop 249 mV (2.1%)
- To stay under 3%, choose AWG 14.
AWG wire size chart
| AWG | Diameter (mm) | Area (mm²) | Resistance (Ω/km, copper 20 °C) |
|---|---|---|---|
| AWG 30 | 0.255 | 0.051 | 338.53 |
| AWG 28 | 0.321 | 0.081 | 212.90 |
| AWG 26 | 0.405 | 0.129 | 133.90 |
| AWG 24 | 0.511 | 0.205 | 84.21 |
| AWG 22 | 0.644 | 0.326 | 52.96 |
| AWG 20 | 0.812 | 0.518 | 33.31 |
| AWG 18 | 1.024 | 0.823 | 20.95 |
| AWG 16 | 1.291 | 1.309 | 13.17 |
| AWG 14 | 1.628 | 2.081 | 8.28 |
| AWG 12 | 2.053 | 3.309 | 5.21 |
| AWG 10 | 2.588 | 5.261 | 3.28 |
| AWG 8 | 3.264 | 8.366 | 2.06 |
Frequently asked questions
How much voltage drop is acceptable?
A common guideline is 3% or less for a single run and 5% or less overall. Low-voltage DC loads such as LED strips and small motors benefit from staying near 3% or below.
How do AWG and mm² sizes compare?
AWG is the American wire gauge, where a smaller number means a thicker wire. Metric sizes give the copper cross-section in mm² directly. AWG 18 is about 0.82 mm², close to 0.75 mm² metric wire.