Specific Resistance Calculator

Calculator

Solve for

Use consistent inputs; the tool converts units automatically.

Material preset

Presets load typical ρ at 20°C and α.

Output formatting

Decimals

Auto switches to scientific for very small/large values.

Resistivity input (ρ)

If solving for ρ, this field can be blank.

Temperature coefficient (α)

Used only when temperature correction is enabled.

Temperature correction

Apply linear temperature adjustment

Reference (°C)

Operating (°C)

Resistance (R)

Required unless you solve for resistance.

Length (L)

Required unless you solve for length.

Area input method

Area must be positive for meaningful results.

Diameter

Width × Height

Area

Example data table

These examples use typical material values at 20°C. Your actual results depend on grade, temperature, and geometry.

Scenario	Material	Length	Geometry	Resistivity	Estimated resistance
Low-voltage feeder	Copper	10 m	Round, 2.0 mm diameter	1.68e-8 Ω·m	≈ 0.0535 Ω
Heating element	Nichrome	1 m	Area 0.50 mm²	1.10e-6 Ω·m	≈ 2.20 Ω
Busbar segment	Aluminum	0.50 m	Rectangular, 20 mm × 3 mm	2.82e-8 Ω·m	≈ 0.000235 Ω

Formula used

ρ = (R × A) / L (resistivity from measured resistance)
R = (ρ × L) / A (resistance from resistivity)
L = (R × A) / ρ (length from resistance and resistivity)
A = (ρ × L) / R (area from resistance and resistivity)

Temperature adjustment (linear approximation): ρ(T) = ρ(Tref) × [1 + α × (T − Tref)].

How to use this calculator

Select what you want to solve for (R, ρ, L, or A).
Choose a material preset or enter resistivity and α manually.
Enable temperature correction if you need operating-temperature estimates.
Provide conductor length and geometry (diameter, rectangle, or direct area).
Enter resistance if it is an input for your chosen solve mode.
Press Submit to display results above the form, then export if needed.

Meaning of specific resistance in conductors

Specific resistance, also called resistivity (ρ), describes a material’s opposition to current flow independent of conductor dimensions. In SI it is Ω·m. At 20°C, copper is about 1.68×10⁻⁸ Ω·m and aluminum about 2.82×10⁻⁸ Ω·m, while nichrome is near 1.10×10⁻⁶ Ω·m for resistive heating.

Unit choices and practical conversion checks

Datasheets often use Ω·mm²/m, equal to 10⁶× the Ω·m value. Another common unit is µΩ·cm, equal to 10⁸× Ω·m. Copper at 1.68×10⁻⁸ Ω·m becomes 0.0168 Ω·mm²/m and 1.68 µΩ·cm. Consistent units prevent scaling errors. This calculator outputs all three forms side by side.

Geometry, area calculation, and measurement tolerance

The governing relation is R = ρL/A. Because A is in the denominator, dimensional uncertainty can dominate. For a round wire, A = π(d/2)²; d = 2.0 mm gives about 3.1416 mm². A 2% diameter error changes area by ~4%, shifting resistance by similar percentage. Use measured four-wire resistance for low values.

Temperature correction and operating range impacts

Many metals increase resistivity with temperature using ρ(T)=ρ(Tref)[1+α(T−Tref)]. Copper often uses α≈0.0039/°C, so 20°C to 80°C raises ρ by ~23.4%. With fixed length and area, resistance rises proportionally, affecting voltage drop and I²R losses on warm cable runs. Match Tref to datasheet condition.

Resistance per meter as a planning metric

Reporting R/L in Ω/m enables quick scaling across layouts. When material and cross section stay constant, doubling length doubles resistance. In the example copper run (10 m, 2 mm diameter), R/L is about 0.00535 Ω/m. Multiply by planned route length, then by circuit current, to estimate drop and losses early.

Applying results to cable sizing and losses

Use the outputs to compare materials, then adjust geometry to meet targets. Increasing area reduces R linearly, while selecting a lower-ρ material reduces R without changing size. Combine resistance with P=I²R to estimate heating. Confirm final choices against insulation limits, installation conditions, and manufacturer data for the exact conductor.

FAQs

1) Is specific resistance the same as resistance?

No. Resistivity is a material property (Ω·m). Resistance depends on geometry and length: R = ρL/A, so two conductors of the same material can have different resistance.

2) Which inputs matter most for accuracy?

Cross-sectional area and temperature usually dominate. Small diameter errors cause larger area errors, and temperature shifts can change resistivity materially, especially for copper and aluminum.

3) When should I enable temperature correction?

Enable it when operating temperature differs from the reference temperature of your material data or test conditions. It improves estimates of in-service resistance, voltage drop, and I²R losses.

4) What unit should I use for area?

Use the unit you measure most reliably. The tool converts mm², cm², m², and in² to SI internally. For cables, mm² is common and matches many catalog specifications.

5) Can I solve for length or area instead of resistance?

Yes. Choose the appropriate solve mode. Provide the other quantities, and the calculator rearranges the same relationship to compute L or A while keeping units consistent.

6) Why does my measured resistance not match the estimate?

Real conductors vary by alloy, strand packing, joints, and contact resistance. Measurement method matters too; for low resistances, use a four-wire technique and verify temperature during testing.