12V DC Wire Gauge Calculator

Minimum AWG for accessory circuits from amp draw, one-way length, and an allowable voltage-drop percent

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Wire, Strippers & Copper You Can Actually Buy

Voltage-drop math assumes copper and a real termination. Stranded primary wire and a stripper that does not nick 10–18 AWG strands are the parts that make the number true.

Klein Tools 11047 Wire Stripper/Cutter 10-18 AWG

Nicked strands raise resistance the calculator never sees. Strip 10–18 AWG without chewing the copper.

View on Amazon →

Southwire Stranded Copper 10 Gauge 500 ft

10 AWG copper is the common upsize when 12 AWG fails a 15–20 ft accessory run at 3%. Confirm the calculator before you buy a spool.

View on Amazon →

Run Your Length, Not the Spool Label

Amps, one-way feet, 12/24V, drop %. Minimum AWG, actual volts, pass/fail.

Open 12V Wire Gauge Calculator →

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How to Use This 12V Wire Gauge Calculator

Read the accessory’s continuous current (or measure it). Measure the one-way path you will actually route — around inner fenders, not a tape-line through the firewall. Leave voltage at 12V unless the bank is a 24V RV/house setup. Leave drop at 3% unless the device specifies a wider window. Calculate, then fuse the chosen wire and crimp like you mean it.

V_drop = I × R × 2 × L / 1000

Worked installs (winch, lights, amp): guide. Symptoms of thin wire: troubleshooting. Overcurrent device choice: fuse vs breaker.

FAQ

Why not just use the fuse size as the amp input?

The fuse is protection, often 125–150% of continuous current. Sizing wire to the fuse overbuilds the copper and still does not tell you voltage at the lamp. Use measured or nameplate continuous current; fuse the wire afterward. Device choice: fuse vs circuit breaker.

Is this the same as the NEC voltage-drop calculator?

No. That tool is 120/240 V premises wiring (and optional 12 V as a source voltage on a building-wire table). This tool is automotive/RV accessory copper with a 12/24V toggle and AWG as the answer. House circuits: voltage drop calculator.

What if even 4/0 fails?

Shorten the run, raise system voltage to 24V if the accessory allows it, or split the load. A 50 ft one-way 80 A 12V feed at 3% is a cable, not a primary-wire problem.

12V DC Wire Gauge Calculator