Wire Resistivity Calculator
Use measured resistance, wire length, and cross-sectional size to calculate resistivity (ρ).
where R = resistance (Ω), A = cross-sectional area (m²), L = length (m)
What this resistivity calculator does
This tool calculates the electrical resistivity of a wire from real measurements. Resistivity is a material property that tells you how strongly a material opposes electric current. Unlike plain resistance, resistivity removes the effect of wire dimensions, so you can compare different materials fairly.
If you have measured resistance for a sample wire and you know its length and size, this calculator returns:
- Resistivity in Ω·m
- Resistivity in Ω·mm²/m (common in wiring work)
- Conductivity in S/m
- An estimated closest common material value at ~20°C
Understanding the formula
The core equation is:
- ρ (rho): resistivity
- R: measured resistance of the wire sample
- A: cross-sectional area of the wire
- L: wire length
If your input is diameter, area is found with:
The calculator handles all mm-to-meter conversions automatically so you can work with practical wire dimensions.
How to use it correctly
1) Measure resistance carefully
Use a reliable meter and keep probe contact resistance low. For very low-resistance wires, four-wire (Kelvin) measurement methods are ideal.
2) Enter true wire length
Use the actual electrical path length. Resistivity scales directly with length, so large length errors create large output errors.
3) Enter diameter or area
For round wire, diameter is convenient. For stranded or non-round conductors, use effective cross-sectional area instead.
4) Keep temperature in mind
Resistivity changes with temperature for most metals. Copper and aluminum, for example, increase in resistance as temperature rises.
Worked example
Suppose you measured a wire and found:
- R = 0.84 Ω
- L = 25 m
- d = 0.60 mm
The calculator computes area from diameter, then applies ρ = R × A / L. The result is around the same order of magnitude as common conductive metals, which helps confirm your measurements are realistic.
Typical resistivity values at 20°C (reference)
- Silver: ~1.59 × 10-8 Ω·m
- Copper: ~1.68 × 10-8 Ω·m
- Gold: ~2.44 × 10-8 Ω·m
- Aluminum: ~2.82 × 10-8 Ω·m
- Tungsten: ~5.60 × 10-8 Ω·m
- Nichrome: ~1.10 × 10-6 Ω·m
These numbers vary slightly by alloy purity and temperature, so treat them as practical reference values, not exact constants for every sample.
Common mistakes to avoid
- Mixing units (mm vs m)
- Using nominal wire size instead of measured diameter
- Ignoring temperature rise during measurement
- Measuring too short a sample (tiny errors become huge percentages)
When this calculator is useful
- Checking unknown wire material
- Lab experiments in electricity and materials science
- Quality checks for cable manufacturing
- DIY and engineering troubleshooting of high-loss conductors