Calculate nichrome wire resistance, length or diameter from resistivity, gauge, temperature and target ohms, with AWG power estimates.

Uniform round wire at a known temperature. Estimates do not establish safe current, power or operating temperature.

Nichrome Resistance Formula

The following formula is used to calculate the resistance of a nichrome wire.

R = p × L / A
  • Where R is the resistance (ohms)
  • p is the resistivity at the wire temperature (ohm-meters); the example assumes 150 × 10^-8 Ω·m
  • L is the length of the wire (m)
  • A is the cross-sectional area of the wire (m^2)

To calculate the resistance of a nichrome wire, multiply the resistivity by the length, then divide by the cross-sectional area of the wire.

What is the resistance of nichrome?

Definition:

Nichrome resistivity depends on alloy and temperature. For example, the manufacturer’s Nikrothal 80 and 60 data give approximately 1.09 × 10^-6 and 1.11 × 10^-6 Ω·m at 20 °C. Wire resistance also depends on its length and cross-sectional area.

How to calculate nichrome resistance?

Example Problem:

The following example outlines how to calculate the resistance of a nichrome wire.

First, use resistivity for the actual alloy and temperature. This example assumes 150 × 10^-8 ohm-meters for illustration.

Next, determine the length of the wire. This wire is 100 m long.

Next, determine the cross-sectional area of the wire. Given a diameter of the wire of .025 m, the cross-sectional area can be calculated with the formula:

πD²/4 = π × .025²/4 ≈ .000490874 m²

Finally, calculate the total resistance using the formula above:

R = p*L / A

R = (150 × 10^-8) × 100 / (π × .025²/4)

R ≈ .305577 ohms (about .306 ohms)