BASICS · CALCULATOR

Resistance calculator

Free resistance calculator for electricians, with clear inputs, an instant result, the equation behind it and a worked example. Verify against the NEC.

Written by Chameera Sampath · Not yet reviewed by a licensed electrician. See the methodology.

US (NEC) only · NFPA 70 / NEC — locally adopted editionDefaults are US values. Verify the locally adopted NEC edition and project data.Official reference ↗

Project inputs

Measurements

Voltage

Current

Updates as inputs change. Unit changes preserve the same physical values.

THE MATH BEHIND THE ANSWER

Method & assumptions

R = V / I

DC / resistive circuit.

Results do not check every aspect of an electrical installation. The calculators follow US (NEC) practice only; a regional preset changes defaults such as voltage and units, and no result certifies NEC compliance.

Sources and validation →

Worked example

Voltage: 120 V · Current: 20 A

Resistance: 6 Ω

This example uses the stated inputs; results for the entered values appear above.

Explore the basics branch →See the related electrical concepts →

Estimating and invoicing tool

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