Estimate voltage drop on a cable run by AWG gauge, length, current and conductor — copper or aluminium, single-phase, DC or three-phase, in volts and percent. Runs entirely in your browser — your numbers never leave this device.
| Gauge (AWG) | Area (mm²) | Drop (V) | Drop (%) |
|---|---|---|---|
| 14 | 2.08 | 2.42 | 1.05 |
| 12 | 3.31 | 1.52 | 0.66 |
| 10 | 5.26 | 0.96 | 0.42 |
| 8 | 8.37 | 0.6 | 0.26 |
| 6 | 13.3 | 0.38 | 0.16 |
| 4 | 21.2 | 0.24 | 0.10 |
| 3 | 26.7 | 0.19 | 0.08 |
| 2 | 33.6 | 0.15 | 0.07 |
| 1 | 42.4 | 0.12 | 0.05 |
| 1/0 | 53.5 | 0.09 | 0.04 |
| 2/0 | 67.4 | 0.07 | 0.03 |
| 3/0 | 85 | 0.06 | 0.03 |
| 4/0 | 107.2 | 0.05 | 0.02 |
This is a resistive sizing estimate using resistivity at 20 °C — it omits reactance, temperature rise and terminations, and it is not a code-compliance check. Verify final sizing against your local electrical code and the cable manufacturer's data.
| Item | Value |
|---|---|
| Copper resistivity (20 °C) | 1.68×10⁻⁸ Ω·m |
| Aluminium resistivity (20 °C) | 2.82×10⁻⁸ Ω·m |
| 14 AWG | 2.08 mm² |
| 12 AWG | 3.31 mm² |
| 10 AWG | 5.26 mm² |
| 8 AWG | 8.37 mm² |
| 6 AWG | 13.3 mm² |
| 4 AWG | 21.2 mm² |
| 3 AWG | 26.7 mm² |
| 2 AWG | 33.6 mm² |
| 1 AWG | 42.4 mm² |
| 1/0 AWG | 53.5 mm² |
| 2/0 AWG | 67.4 mm² |
| 3/0 AWG | 85.0 mm² |
| 4/0 AWG | 107.2 mm² |
Every conductor resists the current through it, so a cable run is a resistor in series with the load and some of the supply voltage is spent along the wire instead of at the load. The resistance of the run is ρ × length ÷ area, where ρ is the conductor's resistivity — 1.68×10⁻⁸ Ω·m for copper and 2.82×10⁻⁸ Ω·m for aluminium at 20 °C. A two-wire circuit pays that resistance twice (out and back), giving VD = 2·L·I·ρ/A; a balanced three-phase circuit replaces the factor 2 with √3. Enter the one-way length, the current and the gauge, and the drop comes back in volts, as a percentage of your supply, and side by side for every AWG gauge on the same run so the effect of going one size up is visible.
Read the result as a sizing estimate, not a verdict. This calculation is purely resistive: it omits cable reactance (which matters on large conductors), the rise in resistivity as a loaded cable warms up, and termination and joint resistance, all of which push the real drop a little higher. Electrical codes set their own drop limits and conductor rules that differ by country and installation type, and nothing on this page is a code-compliance check — use the estimate to shortlist a gauge, then verify the final design against your local code and the cable manufacturer's data.
A single-phase or DC load is fed by two wires and the current travels the full run length in each of them, so the drop is 2 × L × I × ρ/A. A balanced three-phase load shares its return between the three phases, and the line-to-line drop works out to √3 × L × I × ρ/A instead — the same resistivity maths with a different circuit factor.
That is set by your electrical code and by what the load tolerates, not by physics — many codes recommend keeping branch-circuit drop around 3% and total drop around 5% as design guidance, but the binding figure is the one in the code that governs your installation. This page is an estimate to design against those limits, not a compliance check.
Because aluminium's resistivity is higher: 2.82×10⁻⁸ Ω·m against copper's 1.68×10⁻⁸ at 20 °C, a ratio of about 1.68. An aluminium run needs roughly one to two AWG sizes larger than a copper run to land at the same drop — compare both in the gauge table rather than swapping like for like.
Yes — resistivity rises as a conductor warms, roughly 0.4% per °C for copper, so a heavily loaded cable running hot drops more than the 20 °C figure shown here. That is one reason this is an estimate: compare the result against your limit with some margin rather than to the last decimal.
The one-way length — the distance from the supply to the load. The factor 2 in the single-phase formula already accounts for the return conductor, so entering the round trip as well would double-count it and overstate the drop.
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