AWG 4 carrying 125 A — 2.03 V over 10 m
21.151 mm² of copper, 0.00081 Ω per metre. Carrying 125 A, a ten-metre run there and back loses 2.03 V.
You need thicker wire · Current it handles 66.9A
- Diameter
- 5.189 mm
- Cross-section
- 21.151 mm²
- Resistance per metre
- 0.00081 Ω
- Current it handles
- 66.9 A
- Drop over 10 m
- 2.03 V
- Heat per metre
- 12.71 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 V1.8 m
- truck 24 V3.5 m
- North America 120 V17.7 m
- Europe 230 V33.9 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.
6mm²6mm²Nearby 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 4 carry 125 A?
No. This gauge tops out around 66.9 A, so step up to something thicker.
Q. How far can I run it?
The drop stays under 3% for 33.9 m at 230 V, 17.7 m at 120 V, or 1.8 m at 12 V.
Q. How many mm² is AWG 4?
21.151 mm², from a diameter of 5.189 mm. The nearest size in the other family is 6mm².
Q. How hot does the wire get?
Every metre turns 12.71 W into heat. Over ten metres that is a 127.1 W heater left running.