VoltageDrop Tip

Wire gauge chart

The chart below lists every common wire size from 18 AWG to 500 kcmil with its area in square millimetres, its DC resistance per 1000 feet at 75 °C for stranded copper and aluminum, and its ampacity in the 75 °C column. Smaller AWG numbers are bigger wires: every three gauge steps roughly doubles the area and halves the resistance. VoltageDrop uses the same values in the calculator above.

Copper or aluminum, AWG / kcmil

    Saved you some time? Leave a tip, entirely optional.

    For 14, 12 and 10 AWG, NEC 240.4(D) also limits the breaker size to 15, 20 and 30 amps for copper.

    How the voltage drop calculator works

    VoltageDrop uses VD = 2 × I × R × L ÷ 1000 for DC and single-phase circuits and VD = 1.732 × I × R × L ÷ 1000 for three-phase, where I is the current in amps, R the conductor resistance in ohms per 1000 ft and L the one-way length in feet. Percent drop = VD ÷ supply voltage × 100. The suggested wire is the smallest size whose drop is within your limit and whose ampacity covers the current (125% of it for a continuous load).

    Wire gauge chart

    Sizemm²Copper Ω/1000 ftAluminum Ω/1000 ftCopper amps (75 °C)Aluminum amps (75 °C)
    18 AWG0.8237.95———
    16 AWG1.314.99———
    14 AWG2.083.14—20 (15 A breaker)—
    12 AWG3.311.983.2525 (20 A breaker)20 (15 A breaker)
    10 AWG5.2611.242.0435 (30 A breaker)30 (25 A breaker)
    8 AWG8.3670.7781.285040
    6 AWG13.30.4910.8086550
    4 AWG21.150.3080.5088565
    3 AWG26.670.2450.40310075
    2 AWG33.620.1940.31911590
    1 AWG42.410.1540.253130100
    1/0 AWG53.490.1220.201150120
    2/0 AWG67.430.09670.159175135
    3/0 AWG85.010.07660.126200155
    4/0 AWG107.20.06080.1230180
    250 kcmil1270.05150.0847255205
    300 kcmil1520.04290.0707285230
    350 kcmil1770.03670.0605310250
    400 kcmil2030.03210.0529335270
    500 kcmil2530.02580.0424380310

    Resistance: NEC Chapter 9 Table 8, stranded uncoated copper and aluminum, DC at 75 °C. Ampacity: NEC Table 310.16, 75 °C column (not more than three current-carrying conductors, 30 °C ambient); breaker limits for 14–10 AWG from NEC 240.4(D). 18 and 16 AWG are shown for low-voltage DC only.

    Limits of this calculator

    Results are estimates for planning. The calculation uses DC resistance and ignores reactance and power factor, conductor temperature below 75 °C, and derating for heat, conduit fill or bundling. Terminal temperature ratings, insulation type, local codes and the equipment instructions can all require a larger wire. Have a licensed electrician design and inspect mains-voltage work.

    Frequently asked questions

    How many amps can 12 gauge wire carry?

    25 A in the 75 °C column, but the breaker is limited to 20 A by NEC 240.4(D), so 12 AWG copper is used on 20 A circuits.

    What is the resistance of 14 AWG wire?

    About 3.14 ohms per 1000 ft for stranded copper at 75 °C (3.07 for solid).

    How does AWG relate to mm²?

    12 AWG is 3.31 mm², 10 AWG is 5.26 mm² and 6 AWG is 13.3 mm². Metric sizes are close but not identical.

    Is VoltageDrop free?

    Yes, with no sign-up or ads.

    Are my inputs saved?

    Yes, in this browser only.

    More tools