Wire Resistance Calculator
This wire resistance calculator finds the electrical resistance of a conductor from its material, length, and cross-section. Enter the wire gauge or area, the length, and the metal, and the wire resistance calculator returns the resistance in ohms. It uses the copper wire resistance formula by default and also works as a cable resistance calculator for aluminum, nichrome, and other conductors.
Results
The Wire Resistance Calculator is part of our Cable & Protection collection. Browse more cable & protection to size, convert, and check your work alongside this tool.
What the wire resistance calculator does
Every conductor resists the current flowing through it, and that resistance depends on what the wire is made of, how long it is, and how thick. This wire resistance calculator combines those three into a single figure in ohms. As a cable resistance calculator it covers copper, aluminum, and resistance wire like nichrome, so finding resistance of a wire takes one entry instead of a table lookup and a hand calculation.
The copper wire resistance formula
The copper wire resistance formula relates resistance to resistivity, length, and area:
where ρ is the resistivity of the metal, L is the length, and A is the cross-sectional area. Copper has a low resistivity, aluminum a little higher, and nichrome far higher, which is why the same size nichrome wire has much more resistance. To calculate copper wire resistance the wire resistance calculator uses ρ for copper and converts the gauge you enter into an area first.
Copper wire resistance formula example
A 50 m length of 2.5 mm² copper, using the copper wire resistance formula with ρ ≈ 1.72 × 10⁻⁸ Ω·m:
Enter the length, the area, and copper as the material, and the wire resistance calculator returns this. Switch the metal to aluminum and finding resistance of a wire of the same size gives a higher figure.
How to use the wire resistance calculator
Choose the conductor material, enter the length, and enter either the wire gauge or the cross-sectional area. The wire resistance calculator applies the copper wire resistance formula, or the resistivity of whichever metal you pick, and returns the resistance. Enter an AWG number and it acts as an awg wire resistance calculator; enter a longer length and the wire length resistance calculator scales the result directly.
Reading the wire resistance calculator result
The resistance in ohms tells you how much voltage the wire will drop and how much power it will turn into heat at a given current. For power wiring you want this low, so a small resistance from the cable resistance calculator is good news. For a heating element the opposite is true: nichrome is chosen precisely because the nichrome wire resistance calculator shows a high resistance that produces useful heat. Either way, doubling the length doubles the resistance, and doubling the area halves it.
When to use the wire resistance calculator
- Checking voltage loss on a run with the copper cable resistance calculator
- Designing a heating element with the nichrome wire resistance calculator
- Finding resistance of a wire by AWG with the awg wire resistance calculator
- Comparing conductors with the conductor resistance calculator
Common wire resistance calculator mistakes
- Wrong material. Aluminum and nichrome resist far more than copper; pick the metal so the cable resistance calculator uses the right resistivity.
- Half the length. Enter the full conductor length; the wire length resistance calculator counts every meter.
- Ignoring temperature. Hot copper resists more than the cold copper wire resistance formula value.
Tips for accurate results
- Match the material so the wire resistance calculator uses the correct resistivity.
- Use the working temperature for hot runs, not the cold resistance.
- Enter AWG or area consistently so the copper wire resistance formula gets the true cross-section.
What drives the copper wire resistance formula
Three things set a wire resistance, and the copper wire resistance formula shows how each pulls. Resistivity is the material property: copper conducts well, aluminum needs about 60% more area for the same resistance, and nichrome resists roughly sixty times as much as copper, which is the whole point of using it in heaters. Length adds resistance in direct proportion, so a long run resists more than a short one of the same wire. Cross-section works the other way, because a fatter wire gives the electrons more room, so resistance falls as area rises. When you calculate copper wire resistance, changing any one of these moves the answer predictably, and the wire resistance calculator lets you test each without redoing the arithmetic.
Temperature and finding resistance of a wire in practice
Real conductors change resistance with temperature, and copper rises by about 0.4% per degree Celsius. That is small at room temperature but adds up in a hot motor winding or a cable in a warm roof space, so finding resistance of a wire for a demanding application means using the resistance at working temperature, not the cold value. Resistance wire like nichrome is deliberately chosen because its resistance stays fairly stable as it glows, which keeps a heating element predictable. For everyday copper wiring the cold figure from a copper cable resistance calculator is close enough, but for precision work or high-current runs, allow for the rise.
Copper cable resistance calculator chart
Approximate resistance per 100 m of copper wire by gauge, a quick reference from the wire resistance calculator:
| AWG | Area (mm²) | Ω per 100 m (copper) |
|---|---|---|
| 14 | 2.08 | 0.83 |
| 12 | 3.31 | 0.52 |
| 10 | 5.26 | 0.33 |
| 8 | 8.37 | 0.21 |
| 6 | 13.3 | 0.13 |
Wire Resistance Calculator FAQ
What is the copper wire resistance formula?
The copper wire resistance formula is R = ρ × L / A, resistivity times length over area. The wire resistance calculator applies it to calculate copper wire resistance from the gauge and length you enter.
How does length affect resistance?
Resistance is proportional to length, so twice the wire is twice the resistance. The wire length resistance calculator scales the result directly when you change the length.
Can it do nichrome or aluminum?
Yes. Select the material and the cable resistance calculator uses its resistivity. The nichrome wire resistance calculator gives the high resistance used for heating elements.
How do I enter AWG?
Enter the AWG number and the awg wire resistance calculator converts it to a cross-sectional area before applying the copper wire resistance formula.