Watts to Amps & Amps to Watts Calculator

For resistive loads like heaters, power factor is 1. Motors and electronics often have a lower power factor, which increases current for the same watts.

Important: This calculation provides a preliminary estimate. Final conductor and overcurrent protection sizing must account for the NEC as adopted locally, conductor material, insulation temperature rating, ambient temperature, installation method, bundling, terminal ratings, equipment specifications and local amendments. Electrical work should be done or checked by a qualified electrician.

Tapeline — Watts to Amps & Amps to Watts Calculator

Printed October 9, 2026

ConvertWatts → amps
Power1800 W
Current15 A
Voltage120 V
SystemSingle-phase (or DC)
Power factor1

Results update as you type.

A
V
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Watch the step-by-step video

Watch it explained

A step-by-step video using your numbers: what to enter, what the result means, and a “what if” example. On-screen instructions follow each step as it happens.

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What the animation shows

The animation and the step-by-step video above use your numbers. Here is the same walkthrough written out for the default example.

Finished frame of the watts to amps & amps to watts calculator animation for the default example
The last frame of the animation for the default example.

What you enter

  • Convert: Watts → amps.
  • Power: 1800 W.
  • Voltage: 120 V.
  • System: Single-phase (or DC).
  • Power factor: 1.

What happens, step by step

  1. The load needs 1,800 W; the clamp meter reads the current it pulls.
  2. Amps = watts ÷ volts: 1,800 W ÷ 120 V.
  3. Same watts at a higher voltage means fewer amps in the wire.
  4. 15 A at 120 V: size the wire and breaker for that current.

The answer: current is 15 A.

How it’s calculated

  • Single-phase: amps = watts ÷ (volts × PF)
  • Three-phase: amps = watts ÷ (√3 × line volts × PF)
  • kVA = √3 (if three-phase) × volts × amps ÷ 1,000

Worked example

An 1,800 W appliance on 120 V single-phase, power factor 1.

Inputs

Convert
Watts → amps
Power
1800 W
Current
15 A
Voltage
120 V
System
Single-phase (or DC)
Power factor
1

Results

Current
15 A
Power
1,800 W
Apparent power
1.8 kVA

Load this example into the calculator

Assumptions and limits

  • Three-phase uses line-to-line voltage and a balanced load.

Verify the result against the applicable local code, adopted code edition, manufacturer instructions and project requirements. See our methodology.

Questions

How many amps is 1500 watts at 120 volts?

1,500 ÷ 120 = 12.5 A for a resistive load.

How many watts can a 15 amp circuit handle?

15 A × 120 V = 1,800 W, but continuous loads (3 hours or more) are limited to 80% — 1,440 W.