Free Amps to watts calculator
Enter your current in amps and the voltage, pick DC, AC single-phase or three-phase, and this calculator returns the power in watts and kilowatts — using P = V × I, with the power factor applied for AC — updated live, as you type.
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Estimates from the values you enter. Real loads vary with power factor, supply voltage and temperature.
Results are estimates. Consult a professional.
How the amps to watts calculator works
Amperes measure how much current flows; watts measure how much power that current delivers. You cannot turn one into the other without knowing the voltage — power is what you get when current and voltage act together. This calculator takes the current in amps and the voltage in volts, asks whether the circuit is DC or AC, and returns the power in watts and kilowatts. For alternating current it also asks for the power factor, because not all of the apparent power in an AC circuit does useful work.
The DC, single-phase and three-phase formulas
Which formula you use depends entirely on the kind of supply. The current type you pick at the top of the calculator switches between the three.
Direct current (DC) — P = V × I
In a DC circuit — a battery, a solar panel, a USB rail — voltage and current stay steady and move in step, so every amp delivers its full power. Power is just voltage times current: a 12 V supply pushing 5 A delivers 60 W. There is no power factor to worry about; it is effectively 1.
AC single-phase — P = PF × V × I
Household and light commercial outlets are single-phase AC. Voltage and current both alternate, and in many loads they fall slightly out of step. The power factor (PF) captures that mismatch, so the real power is the DC product scaled down by the power factor. A purely resistive load — a heater or an incandescent bulb — has a power factor of 1 and behaves like DC.
AC three-phase — P = √3 × PF × V_line × I
Industrial motors and large equipment run on three-phase AC, which carries power on three conductors offset in time. For a balanced three-phase load the total power is √3 (about 1.732) times the line-to-line voltage, the line current, and the power factor. The most common slip here is voltage: this formula expects the line-to-line voltage, such as 400 V or 480 V, not the lower phase voltage.
What power factor is and why AC needs it
In an AC circuit the voltage and current both rise and fall many times a second. If the load is purely resistive they peak together, and every volt-ampere becomes a watt. But motors, transformers, and many electronic supplies are inductive or capacitive: they store and return energy each cycle, which pushes the current out of step with the voltage. Power factor is the cosine of that phase angle — a number from 0 to 1 — and it tells you what fraction of the apparent power actually does useful work.
- PF = 1.0 — purely resistive (heaters, incandescent lamps, kettles). All the apparent power is real power.
- PF ≈ 0.8–0.95 — typical motors, pumps, and air conditioners under load. A common default for general AC loads is 0.8.
- PF < 0.7 — lightly loaded motors and some electronics. A large gap between volt-amperes and watts.
Because DC has no phase angle, it has no power factor, which is why this calculator hides the power-factor field for DC and shows it only for the two AC options. If you do not know your load's exact power factor, check its nameplate or datasheet; 0.8 is a reasonable starting estimate for a general motor load.
A worked example converting amps to watts
Marcus has a circuit pulling 10 A at 120 V and wants the power in watts. He works it three ways — as DC, as single-phase AC, and then a three-phase case — to see how the supply type changes the answer.
Step 1 — DC: P = V × I
For a DC supply, power is voltage times current: P = 120 × 10 = 1200 W (1.2 kW). This is the calculator's default view, so it shows 1200 W the moment the page loads.
Step 2 — AC single-phase with power factor 0.9
Switch the current type to AC single-phase and set the power factor to 0.9. Now P = 0.9 × 120 × 10 = 1080 W. The 10% phase mismatch costs 120 W of real power compared with the DC case.
Step 3 — AC three-phase at 400 V line, PF 0.9
A balanced three-phase load drawing 10 A per line at 400 V line-to-line, at power factor 0.9, delivers P = √3 × 0.9 × 400 × 10 = 6235.38 W (about 6.24 kW). The √3 factor and the higher line voltage together carry far more power on the same 10 A.
Amps to watts quick-reference table
Common current, voltage, and supply combinations and the power they deliver. Every value comes straight from the formulas above.
| Current | Voltage | Type / PF | Power |
|---|---|---|---|
| 1 A | 120 V | DC | 120 W |
| 10 A | 120 V | DC | 1200 W (1.2 kW) |
| 10 A | 120 V | AC 1φ, PF 1.0 | 1200 W |
| 10 A | 120 V | AC 1φ, PF 0.9 | 1080 W |
| 10 A | 120 V | AC 1φ, PF 0.8 | 960 W |
| 16 A | 230 V | AC 1φ, PF 1.0 | 3680 W (3.68 kW) |
| 10 A | 400 V | AC 3φ, PF 0.9 | 6235 W (6.24 kW) |
| 20 A | 480 V | AC 3φ, PF 0.85 | 14 134 W (14.13 kW) |
DC uses P = V × I; AC single-phase P = PF × V × I; three-phase P = √3 × PF × V_line × I. Three-phase voltages are line-to-line.
Common mistakes converting amps to watts
- Forgetting the power factor on AC. Multiplying volts by amps alone gives volt-amperes (VA), not watts. For anything but a resistive load you must scale by the power factor, or you will overstate the real power.
- Using phase voltage in the three-phase formula. P = √3 × PF × V_line × I expects the line-to-line voltage (e.g. 400 V), not the phase voltage (230 V). Mixing them up gives an answer that is wrong by a factor of √3.
- Applying a power factor to DC. DC has no phase angle, so its power factor is effectively 1. Power is simply V × I — this calculator hides the field for DC so you cannot apply it by mistake.
- Confusing watts with watt-hours. Watts are instantaneous power; watt-hours are energy over time. A 1200 W load running for two hours uses 2400 Wh = 2.4 kWh — power multiplied by hours.
- Reading per-phase vs total power. The three-phase formula gives the total power across all three phases, not the power per phase.
To go the other way — from a known wattage back to the current it draws — use the watts to amps calculator. To check voltage, current, and resistance together, see Ohm's law, and for running costs the electricity cost calculator.
How accurate is this amps to watts calculator
The arithmetic is exact. For the current, voltage, supply type, and power factor you enter, P = V × I (DC), P = PF × V × I (single-phase), and P = √3 × PF × V_line × I (three-phase) are the precise real-power values, computed to full floating-point precision and shown in both watts and kilowatts.
Where real circuits differ is in the inputs, not the formula. Supply voltage sags under load, the power factor of a motor changes with how heavily it is loaded, and a three-phase system is only balanced when the three lines carry equal current. The result is as accurate as the figures you feed it: use the measured voltage and the load's actual power factor — from its nameplate or a power-factor meter — for the closest match to reality. The underlying relationships are standard electrical theory; see the "Electric power" and "AC power" references for the full derivation.
Frequently asked questions about the free Amps to watts calculator
About this Amps to Watts calculator
This calculator runs entirely in your browser — nothing you enter is sent anywhere. It applies the standard power formulas, P = V × I for DC, P = PF × V × I for AC single-phase, and P = √3 × PF × V_line × I for three-phase, and reports the result in watts and kilowatts the moment you change a value.
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