Wire Resistance Calculator
Every wire resists the flow of electricity a little. This estimates the resistance of a straight wire from its length, its thickness and the metal it is made of.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Resistance equals the metal's resistivity times the wire's length, divided by the cross-section area. The area is pi times the radius squared, so a thicker wire has less resistance.
The resistivity figures used here are typical values near 20 degrees Celsius for copper, aluminum and iron. Real wire varies with its purity and temperature, and warmer wire resists more.
Worked example
A wire 50 ft long and 0.08 in thick, made of the metal you picked, has a cross-section area of 0.005 in² and a resistance of about 0.079 ohms.
Questions
Why does thicker wire have less resistance?
A thicker wire gives the current more room to flow, so less is held back. Resistance falls as the area grows.
Does this tell me which wire to use?
No. It only does the math for a straight wire. Choosing wire for a real circuit depends on rules and conditions this does not cover.
Why does the metal matter?
Each metal resists current by a different amount. For the same size and length, copper resists less than iron.
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