Field Tools – Power Calculations

Basic Electrical Math

Enter any two; the third is worked out.

Watts (W)

Volts (V)

Amps (A)

Phase

Load

Unit

Power Factor (for a Watts load)

A number from 0 to 1, from the equipment nameplate.

Voltage (V, line to line; for an Amps load)

Phase

Transformer Size (kVA)

Voltage (V, line to line)

Phase

Load

Unit

Power Factor

Typical for motors at full load. Lightly loaded motors run lower (DOE). Confirm for your equipment.

Voltage (V, line to line; for an Amps load)

Torque (ft·lb)

RPM

Terms

W, V, A: Watts (power), volts and amps.
kW: Kilowatts: real power. 1 kW = 1,000 W.
kVA: Kilovolt-amps: apparent power. Transformers and generators are rated in kVA.
PF, power factor: kW ÷ kVA, a number from 0 to 1.
Single phase, three phase: The type of supply.
Line to line: The voltage measured between two supply lines. Enter this voltage for three phase.
Transformer size: The kVA rating needed for the load.
Max output current: The amps a transformer of that kVA can supply at that voltage.
Generator size: The kVA rating needed for the load, and the kW that is at the power factor entered.
HP: Horsepower = torque (ft·lb) × RPM ÷ 5252.
RPM: Revolutions per minute.