AWG 12 carrying 125 A — 13 V over 10 m
3.309 mm² of copper, 0.0052 Ω per metre. Carrying 125 A, a ten-metre run there and back loses 13 V.
You need thicker wire · Current it handles 20A
- Diameter
- 2.053 mm
- Cross-section
- 3.309 mm²
- Resistance per metre
- 0.0052 Ω
- Current it handles
- 20 A
- Drop over 10 m
- 13 V
- Heat per metre
- 81.22 W
Length within 3%
Lose the same 0.36 V and it is 3% of a 12 V system but 0.16% of a 230 V one. That is why car wiring looks so thick, and why a long 12 V light run dims at the far end. This page works out the length that stays under 3% for each voltage separately.
- car 12 V0.3 m
- truck 24 V0.6 m
- North America 120 V2.8 m
- Europe 230 V5.3 m
The match in the other family
The United States names wire by AWG number; most of the world names it by cross-section in mm². The two never line up exactly, so each page shows the nearest match by area. When substituting, err toward the thicker one.
4mm²4mm²Nearby cells
Same gauge, other currents
Same current, other gauges
How to read this
- The length is the distance from source to device. The return trip is already counted.
- Figures are for copper. Aluminium of the same size has about 1.6 times the resistance.
- The "current it handles" is a cautious estimate. Real installations follow the local code table.
- A wire running hot and a lamp dimming at the far end are two different problems. Pick a gauge that answers both.
Frequently asked questions
Q. Can AWG 12 carry 125 A?
No. This gauge tops out around 20 A, so step up to something thicker.
Q. How far can I run it?
The drop stays under 3% for 5.3 m at 230 V, 2.8 m at 120 V, or 0.3 m at 12 V.
Q. How many mm² is AWG 12?
3.309 mm², from a diameter of 2.053 mm. The nearest size in the other family is 4mm².
Q. How hot does the wire get?
Every metre turns 81.22 W into heat. Over ten metres that is a 812.2 W heater left running.