4mm² carrying 3 A — 0.26 V over 10 m
4 mm² of copper, 0.0043 Ω per metre. Carrying 3 A, a ten-metre run there and back loses 0.26 V.
This gauge handles it · Current it handles 22.7A
- Diameter
- 2.257 mm
- Cross-section
- 4 mm²
- Resistance per metre
- 0.0043 Ω
- Current it handles
- 22.7 A
- Drop over 10 m
- 0.26 V
- Heat per metre
- 0.04 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 V14 m
- truck 24 V27.9 m
- North America 120 V139.5 m
- Europe 230 V267.4 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.
AWG 123.309mm²Nearby 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 4mm² carry 3 A?
Yes. This gauge is comfortable up to 22.7 A.
Q. How far can I run it?
The drop stays under 3% for 267.4 m at 230 V, 139.5 m at 120 V, or 14 m at 12 V.
Q. How many mm² is 4mm²?
4 mm², from a diameter of 2.257 mm. The nearest size in the other family is AWG 12.
Q. How hot does the wire get?
Every metre turns 0.04 W into heat. Over ten metres that is a 0.4 W heater left running.