Watts to Amps Calculator
Enter watts and voltage to estimate current for DC or AC.
Convert watts to amps
Single-phase AC
Compare loads on one circuit
Compare up to 25 loads. Enter each load's running watts, quantity, and power factor. Mark a load only when you expect it to run continuously for 3 hours or more at the entered running watts.
Planning amps = other running amps + 1.25 × rows marked continuously operating. This is a user-selected arithmetic comparison; 100%-rated equipment and nameplate or manufacturer instructions can require different treatment.
Watts to amps formulas
DC: I = P ÷ V. For single-phase AC, I = P ÷ (V × PF). For balanced three-phase AC with line-to-line voltage, I = P ÷ (√3 × VLL × PF). I is current in amperes, P is real power in watts, V is voltage, and PF is power factor.
Examples at 120 volts
| Mode | Inputs | Current |
|---|---|---|
| DC | 1,500 W, 120 V | 12.5 A |
| Single-phase AC | 1,500 W, 120 V, PF 0.8 | 15.625 A |
| Three-phase AC | 1,500 W, 208 V line-to-line, PF 0.8 | ≈ 5.20448 A |
How the multi-load planning total works
The secondary module is limited to single-phase AC so every row uses the same visible rule: watts × quantity ÷ (shared voltage × row power factor). Running amps are the arithmetic sum of the estimated RMS current magnitude for each row. Planning amps apply the page's visible 1.25 comparison factor to rows the user marks as expected to operate continuously for 3 hours or more at the entered running watts. Some 100%-rated equipment and equipment labels or manufacturer documentation may require different treatment. This assumption does not determine code compliance.
Planning boundary
Electrical planning reference only. Do not use this result alone to choose a breaker, conductor, receptacle, or installation. The displayed current and utilization percentages do not evaluate startup or inrush current, equipment nameplate requirements, wiring, ambient or conductor temperature, receptacle limits, voltage drop, installation details, or applicable code. The planner also excludes phase angle, leading or lagging current, harmonics, and shared-neutral effects. Confirm equipment labels, manufacturer documentation, and local requirements with a qualified professional or the authority responsible for the installation. The page does not model unbalanced three-phase loads.
Frequently asked questions
How do I convert watts to amps?
For DC, divide watts by volts. For single-phase AC, divide watts by volts times power factor. For balanced three-phase AC using line-to-line voltage, divide watts by the square root of 3 times voltage times power factor.
Why does the AC calculation need power factor?
Watts describe real power, while AC current also depends on power factor. Use the documented value for the load. A value of 1 represents unity power factor.
Which voltage should I enter for three-phase AC?
This calculator's three-phase formula expects line-to-line voltage for a balanced load. It does not calculate an unbalanced phase-by-phase system.
What does the circuit-load comparison include?
It adds the arithmetic magnitudes of each single-phase load's estimated RMS current and applies a user-selected 1.25 planning factor only to rows expected to operate continuously for 3 hours or more at the entered running watts. It does not combine phase angle, leading or lagging current, harmonics, or shared-neutral effects. The percentages compare those totals with the selected 15 A or 20 A reference value; they are not breaker or wiring recommendations.
Can this page determine my electrical installation?
No. The result is a planning reference. Confirm equipment documents and applicable requirements with a qualified professional or the authority responsible for the installation.