Watts, Amps & kVA Calculator

A watts to amps calculator converts between real power in watts, apparent power in kVA, and current in amps for a single-phase or three-phase circuit. It divides power by voltage and power factor, with the square root of 3 added to the denominator for three-phase, so you get the amp draw of a load.

Last reviewed September 2026Method & sources Report an error

Current

15.00 A

Breakdown
Current	15.00 A
Real Power	3,600.0 W
Apparent Power	3.600 kVA

How to Calculate Watts, Amps & kVA

Real power (watts) is the power actually doing useful work. Apparent power (kVA) is what the voltage and current alone would suggest, before power factor (the ratio between the two) is applied. The relationship is kVA = watts ÷ power factor. For a single-phase circuit, current is `amps = watts ÷ (voltage × power factor)`. For three-phase, the same relationship uses `√3 × voltage` in place of voltage alone, since three-phase power splits across three conductors rather than one. A power factor of 1 (the default) represents a purely resistive load, where real and apparent power are equal.

Example: 3,600 W single-phase load on a 240 V circuit, power factor 1

A 3,600 W single-phase load on a 240 V circuit, power factor 1: 1. Amps: 3,600 ÷ (240 × 1) = 15 A 2. Apparent power: 3,600 ÷ 1,000 = 3.6 kVA For a three-phase example, take a 10 kVA load at 480 V: 1. Amps: (10 × 1,000) ÷ (√3 × 480) = 10,000 ÷ 831.4 ≈ 12.03 A

What Is Watts, Amps & kVA?

A watts-to-amps (and kVA-to-amps) calculator converts between the three ways electrical load is commonly expressed (real power in watts, apparent power in kVA, and current in amps) for either a single-phase or three-phase circuit. It's the conversion behind sizing a breaker or wire from a device's wattage rating, or checking a generator's kVA rating against the actual amp draw it can support.

Watts, Amps & kVA: Pros and Cons

Pros

Handles both directions (watts to amps and kVA to amps) in one calculator
Covers single-phase and three-phase circuits with the correct √3 multiplier for three-phase
Power factor is adjustable, so a non-resistive load (motors, electronics) can be modeled instead of assuming a perfect 1.0

Cons

Doesn't know your actual load's real-world power factor. A motor nameplate or manufacturer spec sheet is the right source for that, not a guess
Assumes a balanced three-phase load (equal current on all three legs). An unbalanced load needs each phase checked separately
This is a conversion between power/current values, not a wire or breaker sizing tool. See the Voltage Drop calculator for wire sizing on a specific run

Watts, Amps & kVA: What a Pro Checks

Check the equipment nameplate for its actual power factor rather than assuming 1.0. Motors and electronics often run lower, typically 0.8 to 0.95, which changes the real amp draw.
Confirm a three-phase load is actually balanced across all three legs before using this calculator's single-current result. An unbalanced load needs each phase checked separately.
Use this for the watts/kVA/amps conversion only. For wire or breaker sizing on a specific run, check the Voltage Drop calculator instead.

Frequently Asked Questions

How do you convert watts to amps?

For single-phase: amps = watts ÷ (voltage × power factor). A 3,600 W load at 240 V with a power factor of 1 draws 3,600 ÷ 240 = 15 A. For three-phase, use amps = watts ÷ (√3 × voltage × power factor) instead.

How do you convert kVA to amps?

For single-phase: amps = (kVA × 1,000) ÷ voltage. For three-phase: amps = (kVA × 1,000) ÷ (√3 × voltage). A 10 kVA three-phase load at 480 V draws (10,000) ÷ (1.732 × 480) ≈ 12.03 A.

What's the difference between watts and kVA?

Watts measure real power. That is the power actually doing useful work. kVA (kilovolt-amps) measures apparent power, what voltage and current alone suggest before power factor is applied. They're equal only when power factor is 1 (a purely resistive load). Otherwise kVA is always equal to or greater than the real power in kW.

Why does three-phase use √3 in its formula?

Because three-phase power is delivered across three conductors with voltages offset by 120°, and √3 (about 1.732) is the factor that correctly relates line voltage and current to total power delivered. It falls directly out of the three-phase power derivation.

What power factor should I use if I don't know the load's actual value?

A power factor of 1.0 assumes a purely resistive load (like a heater or incandescent bulb) and gives the most conservative (lowest) amp draw for a given wattage. Motors and electronics typically run below 1.0 (often 0.8-0.95). Check the equipment's nameplate for its actual rated power factor if precision matters.

Electrical