Extension Cord Power Loss Calculator

How the result is calculated

This page evaluates loss = I²R. The participating entries are Load current and Round-trip cord resistance.

For the example shown, cord loss equals 60.48 W. Treat that value as a demonstration, not a recommendation.

Calculate cord loss from load current and round-trip cord resistance. If you also need contact power loss, continue with Contact Resistance Loss Calculator.

A second scenario

Change Load current from 12 A to 14.399999999999999 A while preserving the other measurements. The output changes from 60.48 W to 87.09 W.

Keep both cases when the changed input represents genuine uncertainty.

Values this page needs

Record ambient temperature, bundling, insulation class, and termination conditions. Nameplate and meter values are not interchangeable unless they describe the same condition.

Confirm decimal placement whenever a source uses a different unit scale. A connected part of the work can be checked with LED Strip Voltage Loss Calculator.

Load current

Default example: 12 A. Enter load current in A.

Round-trip cord resistance

Default example: 0.42 Ω. Enter round-trip cord resistance in Ω.

Input quality checks

A plausible-looking output does not prove that the entries are compatible.

Recheck decimal placement and unit conversion when the answer looks unusual.

Reading Cord loss

The calculated Cord loss is meaningful only with its input conditions attached. Compare it with ampacity, voltage-drop, fault-current, and protection limits.

Label alternate cases rather than overwriting the baseline. Continue with Wire Power Loss Calculator to evaluate wire loss.

What the formula leaves out

Coiled cords and warm surroundings reduce cooling.

The arithmetic intentionally leaves out termination heating, installation method, ambient temperature, and grouping. Resolve material omissions before selecting a standard size or rating.

Keep one-way and round-trip lengths clearly identified.

A practical checking sequence

Check the source of load current before calculating. A credible result requires every field to describe the same physical condition and unit basis.

After calculating cord loss, compare its magnitude with the applicable installation and equipment requirements. An independent order-of-magnitude check can reveal a misplaced decimal or unit prefix.

Keep a baseline and vary the least certain measurement first. A separate analysis may be needed for code rules, manufacturer instructions, and field installation details.

Before relying on the answer