2.5mm² carrying 20 A — 2.75 V over 10 m
2.5 mm² of copper, 0.00688 Ω per metre. Carrying 20 A, a ten-metre run there and back loses 2.75 V.
You need thicker wire · Current it handles 16.7A
- Diameter
- 1.784 mm
- Cross-section
- 2.5 mm²
- Resistance per metre
- 0.00688 Ω
- Current it handles
- 16.7 A
- Drop over 10 m
- 2.75 V
- Heat per metre
- 2.75 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 V1.3 m
- truck 24 V2.6 m
- North America 120 V13.1 m
- Europe 230 V25.1 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 142.081mm²Nearby 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 2.5mm² carry 20 A?
No. This gauge tops out around 16.7 A, so step up to something thicker.
Q. How far can I run it?
The drop stays under 3% for 25.1 m at 230 V, 13.1 m at 120 V, or 1.3 m at 12 V.
Q. How many mm² is 2.5mm²?
2.5 mm², from a diameter of 1.784 mm. The nearest size in the other family is AWG 14.
Q. How hot does the wire get?
Every metre turns 2.75 W into heat. Over ten metres that is a 27.5 W heater left running.