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Amperage Calculator

Calculate current draw (amps) from power and voltage, single or 3-phase.

Introduction

Amperage Calculator — Calculate current draw (amps) from power and voltage, single or 3-phase. Enter Power (W), Voltage (V), Power factor, Phase to get an instant, accurate result.

Formula

Single-phase: I = P / V (or P / (V × PF) with power factor). Three-phase: I = P / (V × √3 × PF), where V is line-to-line voltage.

Step-by-step

  1. Enter the Power (W).
  2. Enter the Voltage (V).
  3. Enter the Power factor.
  4. Enter the Phase.
  5. Click Calculate to see your result instantly.

Real-world example

Example: With Power (W) = 1200, Voltage (V) = 120, Power factor = 1, Phase = no, the Amperage Calculator gives Amps: 10, Power Factor Used: 1, Three Phase: no.

Frequently Asked Questions

Why does three-phase current use √3?
In a balanced three-phase system, total power is P = √3 × V_line × I_line × PF, so solving for current introduces the √3 (≈1.732) factor versus a single-phase circuit.
Is this the same current I should use to size a breaker?
This gives the operating current draw. For sizing a breaker or wire, that current must still be run through the NEC 210.20 125% continuous-load rule if the load runs 3+ hours continuously.
What inputs does the Amperage Calculator need?
You'll need to provide: Power (W), Voltage (V), Power factor, Phase. All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.
How accurate is the Amperage Calculator?
The Amperage Calculator applies the formula exactly as calculated — Single-phase: I = P / V (or P / (V × PF) with power factor). Three-phase: I = P / (V × √3 × PF), where V is line-to-line voltage. — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.
Is the Amperage Calculator free to use?
Yes, the Amperage Calculator is completely free, requires no signup, and runs instantly in your browser.

About the Amperage Calculator

The Amperage Calculator uses a real, verifiable formula — Single-phase: I = P / V (or P / (V × PF) with power factor). Three-phase: I = P / (V × √3 × PF), where V is line-to-line voltage. — so results are accurate every time, not an approximation.