12V Wire Gauge Chart

The 5% rule (sometimes 10%)

In a 12 V system, 5% loss is 0.6 V — the line where LEDs dim, pumps slow and inverters start protesting. Conservative DC design keeps the round-trip drop under 3% (0.36 V); rugged or heat-tolerant loads tolerate 10%. Whatever ceiling you choose, the chart is the same tool: divide the allowed volts by the amps you're drawing to get a resistance budget, then find the gauge and length that stay inside it.

Quick picks by load

• Under 10 A, under 15 ft: 14 AWG.
• 10–20 A (nav lights, fridge, water pump): 12 AWG short, 10 AWG past ~12 ft.
• 20–40 A (winch logic side, inverter DC input, bow thrusters under 1 kW): 8 AWG, doubling to 4 AWG on longer runs.
• Starter-class loads (100 A+): 2–4 AWG run directly to the battery with short, fat runs — the resistance budget is tiny at those currents.

Fuse the wire, not the device

The circuit protection in a 12 V harness protects the cable against shorts. Size the fuse to the wire's ampacity margin (about 150% of the load usually works for parts that have inrush), and place it as close to the battery positive as practical — an unfused run from the battery to a fuse block has no protection at all.

12V DC wire gauge chart: working the runs by amps × feet

Run the budget once and the picks become mechanical. A 15 A load over 10 ft on 14 AWG burns 0.45 V round trip — 3.7% of supply, at the edge of the 3% target. The same 15 A over 30 ft needs 8 AWG to land inside 3%, or 10 AWG if your devices tolerate 5%. A 3 A LED array is easy: 10 ft on 18 AWG loses just 0.19 V, but double it to 20 ft and you're at 0.38 V — start thinking 16 AWG. And starter-class current flips the logic entirely: the 100 A+ momentary draw wants 2 AWG or thicker run short, because simple resistance mathematics against a 12 V rail is merciless. The automotive wire gauge chart tabulates those chassis-scale picks with free-air ratings so engine-bay math stays honest.

Voltage drop: the numbers behind the picks

Every DC pick is just Ohm's law: drop = current × round-trip resistance. Because a 12 V system has so little voltage to give away, one restriction does the deciding: hold the round-trip drop under 3% where electronics live (0.36 V), accept 5% for motors and heaters (0.6 V), and only near starter circuits does 10% count. Round-trip resistance is two-way by definition — a 10 ft run counts as 20 ft of wire. Adopt the number from the Ω/1000 ft column and divide; that is what the calculator does for any gauge × amps × feet combinations, along with showing the volts that actually arrive at the far end.

From vehicles to solar: the same chart, new jackets

Every 12 V discipline shares this chart and divides it to taste. Under the hood, the ground return and the positive feed count both, and chassis grounds are only "free" when the path is genuinely clean — hence the rule about grounding near the load and fusing near the battery. Solar-side battery banks, inverters and DC-DC converters behave like any other 12 V load, except that inverter input surges dwarf the continuous spec — size those leads one or two steps thicker than the nameplate. The low voltage wire gauge chart covers the 18–12 AWG end where controllers and keypads live, and an AWG↔mm² converter translates any pick into the metric cable a marine or RV supplier will sell you.