Cable Size & Wire Gauge Calculator

It works out the smallest standard conductor that keeps the voltage drop on a run within your chosen limit. Enter the supply type, voltage, current and one-way length in feet (m), pick copper or aluminum and the drop you’ll allow, and it recommends a cable size / wire gauge in AWG/kcmil (mm²) along with the actual drop that gauge delivers.

Cable sizing balances two limits: voltage drop and ampacity. This cable sizing calculator handles the voltage-drop side — it finds the smallest conductor that keeps the drop over your run inside the percentage you set. For a full electrical cable size you also confirm the conductor’s current-carrying capacity from the NEC (or IEC) tables and size up if that is larger. In practice, short runs are usually decided by ampacity and long runs by voltage drop.

It reverses the volt-drop formula. From your limit it finds the largest drop you’ll accept in volts, then solves for the conductor area that keeps drop = k × I × L × (resistivity ÷ area) inside that figure — where k is 2 for DC and single-phase or √3 for three-phase — and rounds up to the next standard AWG or kcmil size.

No — it sizes purely on voltage drop. Ampacity (current-carrying capacity) depends on the installation method, insulation type, grouping and ambient temperature, which vary too much to assume. A wire can be big enough for volt-drop yet still need to be larger to carry the current safely, so always check both — the NEC ampacity tables and volt-drop — and use the bigger size.

Enter the one-way route length — the distance from the supply to the load, in feet (m). The calculator already accounts for the return path (the ×2 for single-phase and DC), so you should not double the length yourself.

Copper has about a third less resistance than aluminum of the same size, so an aluminum run needs to be one or two AWG sizes larger to hold the same voltage drop. Aluminum is lighter and cheaper for big feeders, while copper is usual for smaller branch circuits. Pick the material you’ll actually install and the tool sizes it accordingly.

Wire only comes in standard steps — 14, 12, 10, 8, 6 AWG and so on (2.5, 4, 6, 10, 16 mm²) — so the tool rounds up to the next one that meets your limit. A small change in current or length can push the required area just past a step, moving the recommendation up a gauge: a 20 A, 240 V load over 100 ft lands on about 10 AWG (6 mm²) copper, but stretch the run and it steps up to 8 AWG (10 mm²). The actual-drop figure shows how much headroom the chosen size leaves.