DC wire size calculator.
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DC wire size & voltage drop calculator. Trace your cable run, set a voltage-drop target, and compare the wire sizes that meet it.
6 m total conductor · 12 AWG
12 AWG
3.309 mm² conductor area
0.6253 V lost · 12.51 W in the cable
31.26 mΩ total circuit resistance
Voltage-drop check only. Before choosing a cable, verify its ampacity, insulation temperature rating, terminals and fuse requirements for your installation.
12 AWG, 5.211 percent voltage drop. Above your target. Ampacity requires a separate check.
What changes with a thicker wire?
Select a size to inspect it.
Smaller AWG numbers mean thicker wire.
Conductor drawings show relative size within this comparison. They are not life-size cable measurements.
How DC wire sizing works
A cable loses voltage because its conductor has resistance. More current or a longer run increases the drop. More conductor area reduces it. This calculator finds the minimum area for your target, then checks even-numbered gauges plus 1 AWG and 1/0 through 4/0. Select “Include every AWG size” to include the other odd-numbered gauges. Cable availability varies, so check the sizes your supplier stocks.
Voltage drop (V) = current × resistance
Minimum area = resistivity × total length × current ÷ allowed drop
For example, 20 A through a 3 m one-way copper run at 12 V needs about 5.75 mm² to stay within 3% drop. 10 AWG falls just short at about 3.28%; 8 AWG gives about 2.06%. These are calculated conductor losses at the entered current.
Where the numbers come from
AWG geometry and the 20 °C annealed-copper reference resistivity of 0.017241 Ω·mm²/m follow NBS Handbook 100, Copper Wire Tables. Other materials use approximate resistivity values. For alloyed wire, use the cable maker’s resistance specification. Real cable resistance varies with alloy, construction and temperature.
Victron’s Wiring Unlimited explains conductor loss and the additional resistance from connections. This estimate covers the cable; it excludes fuses, switches, terminals and other contact resistance.
Before you choose the cable
Does meeting the drop target mean the wire can carry the current?
No. Voltage drop and ampacity are separate checks. Ampacity depends on the cable construction, insulation, temperature, bundling and installation. Check the cable datasheet and applicable installation requirements. This tool does not choose a fuse or certify a cable as safe.
Should I enter one-way or round-trip length?
For a separate positive and return cable of equal length, enter the one-way distance and leave “One way” selected. We double it. If you already added both lengths, select “Positive + return combined” to avoid doubling twice. A chassis return needs its own resistance assessment.
Which voltage should I use for a 12V, 24V or 48V battery?
Use the source voltage at the operating point you want to check. A battery’s voltage changes with charge and load. For a device drawing constant power, current rises as voltage falls, so check the low-voltage operating case using the corresponding current.
Why might a real cable lose more voltage?
Warm conductors have more resistance. Stranding, alloy composition, cable tolerances and connections can also change the result. Copper-clad aluminium is not the same material as copper. Use manufacturer resistance data and measurements when refining a build.