# Resistance Calculator

> Calculate resistance step by step: R = V ÷ I, or for a conductor R = ρ × L ÷ A (A in m²).

Page: https://freecalculator.tech/tools/resistance-calculator
Last reviewed: 2026-11-03

## Formula

R = V ÷ I, or for a conductor R = ρ × L ÷ A (A in m²).

- Area entered in mm² is converted to m² by multiplying by 10⁻⁶.
- Resistivity values are entered by you; typical 20 °C values are given as help text only.
- Current must be non-zero for the V ÷ I method.
- R = V ÷ I, or for a conductor R = ρ × L ÷ A (A in m²).
- Inputs used: Method, Voltage, Current, Resistivity ρ, Conductor length, Cross-sectional area.

## Inputs

- Method
- Voltage
- Current
- Resistivity ρ
- Conductor length
- Cross-sectional area

## Worked example: 10 m of 1.5 mm² copper

Resistance of one conductor.
1. A = 1.5 × 10⁻⁶ m².
2. R = 1.68 × 10⁻⁸ × 10 ÷ 1.5 × 10⁻⁶ = 0.112 Ω.

## Common questions

### Does temperature change resistance?

Yes. Copper's resistance rises roughly 0.39% per °C. The calculation uses the resistivity you enter, so enter a value for the operating temperature if it matters.

### Is the length one way or round trip?

It is the length of the conductor you enter. For a circuit's total loop resistance, enter twice the one-way cable length.

### Why can't current be zero?

R = V ÷ I would divide by zero. With no current flowing, resistance cannot be measured this way; use an ohmmeter instead.

### How do I use the Resistance Calculator?

Enter the required values for Method, Voltage, Current, Resistivity ρ, Conductor length, and the other fields shown. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.

### What formula does the Resistance Calculator use?

R = V ÷ I, or for a conductor R = ρ × L ÷ A (A in m²). The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.

### Can the Resistance Calculator be used for exact decisions?

Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.

## Limitations and assumptions

- Single temperature; no temperature coefficient applied.
- DC resistance only — skin effect at high frequency is ignored.
- Resistivity is user-entered, not looked up.
- Results are estimates for planning and learning. Real designs, installations and bids must be checked by a qualified, licensed professional against the codes that apply where you work.
- The result depends on the values you enter for this resistance calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.

## Sources

- OpenStax (Rice University) — https://openstax.org/details/books/university-physics-volume-2

## Cite this page

- APA: Free Calculator. (2026, November 3). Resistance Calculator. https://freecalculator.tech/tools/resistance-calculator
- MLA: "Resistance Calculator." Free Calculator, 3 Nov. 2026, https://freecalculator.tech/tools/resistance-calculator.
- Link: Resistance Calculator — Free Calculator, https://freecalculator.tech/tools/resistance-calculator