Wire Voltage Drop Calculator (AWG & mm²)
Round-trip voltage drop, percent loss and wasted watts for any cable run — copper or aluminium, AWG or metric.
Low-voltage systems hurt most: 0.5 V is 4 % of a 12 V solar/automotive system but only 0.2 % of mains. Resistance rises ~0.4 %/°C — a cable at 60 °C drops ~15 % more than this 20 °C figure. Aim for ≤ 3 % on critical branches; for battery charging, drop directly subtracts from the charge voltage and can stop a battery from ever reaching full.
Wire Voltage Drop Calculator computes the round-trip voltage lost in a cable run and the watts it wastes — free, instant and private in your browser. Solar/camper builders, automotive wirers and anyone whose 12 V gear browns out at the far end use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About Wire Voltage Drop Calculator (AWG & mm²)
Wire Voltage Drop Calculator computes the round-trip voltage lost in a cable run and the watts it wastes using the standard engineering relation: Vd = 2·I·(ρ/A)·L — the 2 covers the return conductor; copper ρ = 1.72×10⁻⁸ Ω·m. Worked live: 10 A over 5 m of AWG 14 copper drops 0.42 V — 3.5 % of a 12 V system, right at the limit. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use Wire Voltage Drop Calculator (AWG & mm²)
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use Wire Voltage Drop Calculator (AWG & mm²)?
- ✓Implements the real formula — Vd = 2·I·(ρ/A)·L — the 2 covers the return conductor — with the substitution shown, not a black box
- ✓Built for solar/camper builders, automotive wirers and anyone whose 12 V gear browns out at the far end
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate wire voltage drop?+
The round-trip voltage lost in a cable run and the watts it wastes follows Vd = 2·I·(ρ/A)·L — the 2 covers the return conductor; copper ρ = 1.72×10⁻⁸ Ω·m. For example, 10 A over 5 m of AWG 14 copper drops 0.42 V — 3.5 % of a 12 V system, right at the limit. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
What percent voltage drop is acceptable?+
Common practice: ≤ 3 % on critical branches, ≤ 5 % total. Low-voltage systems are the unforgiving ones — half a volt is nothing at 230 V and a big deal at 12 V, which is why battery and solar wiring uses such thick cable.
Why is my battery never reaching full charge over a long cable?+
Charge controllers regulate the voltage at THEIR terminals; the cable drop subtracts from what the battery sees, so a 0.4 V drop can leave an absorption stage permanently short. Fixes: thicker wire, shorter run, or a controller with remote voltage sense.
Is the Wire Voltage Drop Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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