BASICS · CALCULATOR

Voltage calculator

Free voltage calculator: get voltage from active power, current and power factor. The formula and a worked example are 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

Active power

Current

SupplyPower factor

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

THE MATH BEHIND THE ANSWER

Method & assumptions

V = P / (k × I × PF)

Three-phase voltage is line-to-line.

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

Active power: 3,000 W · Current: 20 A · Supply: Single phase · Power factor: 0.85

Voltage: 176.471 V

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.