MOTORS · CALCULATOR

Single-phase motor run capacitor

Free Single-phase motor run capacitor: get equivalent capacitance from measured capacitor current, measured capacitor voltage and frequency.

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

Measured capacitor current

Measured capacitor voltage

Frequency

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

THE MATH BEHIND THE ANSWER

Method & assumptions

C = IC / (2πfVC)

Measurement relation only, not a motor capacitor sizing recommendation. Use manufacturer run/start capacitor specifications.

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

Measured capacitor current: 1 A · Measured capacitor voltage: 240 V · Frequency: 60 Hz

Equivalent capacitance: 11.052 µF

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

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