BASICS · CALCULATOR

Joule effect calculator

Free joule effect calculator: get heat energy and power from current, resistance and duration. The formula is shown; 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

Current

Resistance

Duration

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

THE MATH BEHIND THE ANSWER

Method & assumptions

E = I²Rt

No heat transfer or temperature model.

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

Current: 20 A · Resistance: 10 Ω · Duration: 60 s

Heat energy: 240,000 J · Power: 4,000 W

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

Ampxa is developing an estimating and invoicing application for electrical contractors. The list below receives notice when it opens.