Volts to Watts Calculator

To convert volts to watts, multiply voltage by current and by power factor: W = V × A × PF. On DC or a purely resistive load the power factor is 1, so 120 V × 5 A × 1 = 600 watts. For three-phase systems, multiply the result by √3 (about 1.732) using the line-to-line voltage. The calculator above handles DC, single-phase, and three-phase and also reports kilowatts and apparent power (VA).

Voltage by itself cannot be converted to watts — power is the product of voltage and current. You need both, plus the power factor for AC loads that are not purely resistive. Once you supply voltage and current, the wattage is fully determined for DC and resistive circuits; inductive AC loads require the power factor to find the true (real) power that does useful work.

The general power equation adapts to the circuit type:

Each term has a distinct role:

• Volts (V) — the electrical potential difference driving current through the load.
• Amps (A) — the current flowing through the circuit.
• Power factor (PF) — the fraction of apparent power that becomes real, useful work. It ranges from 0 to 1; resistive loads are 1.0, inductive loads are less.
• √3 factor — for balanced three-phase power using line-to-line voltage, the constant √3 ≈ 1.732 accounts for the 120° phase relationship between the three lines.

On DC there is no phase difference, so power factor is always 1 and W = V × A exactly. The same holds for resistive AC loads, where voltage and current stay in phase and the power factor is effectively 1. Only when inductance or capacitance shifts the current out of phase does the power-factor term drop below 1 and pull real watts below apparent VA. To reverse this and find voltage from watts, use the watts to volts calculator. To find current from watts and volts, use the watts to amps calculator. For three-phase specifics, see the 3-phase power calculator.

These examples span DC, single-phase, and three-phase circuits with the arithmetic shown.

Example 1 — Standard outlet load: A device on a 120 V circuit draws 5 A at power factor 1. Power = 120 × 5 × 1 = 600 W. This is why a 15 A, 120 V circuit tops out near 1,800 W before the breaker trips.

Example 2 — Inductive 240 V load: A single-phase motor on 240 V draws 10 A at power factor 0.9. Real power = 240 × 10 × 0.9 = 2,160 W, while apparent power = 240 × 10 = 2,400 VA. The 240 VA difference is reactive power the utility must supply but which does no work.

Example 3 — Three-phase motor: A 480 V three-phase motor draws 20 A per line at power factor 0.9. Real power = √3 × 480 × 20 × 0.9 = 1.732 × 480 × 20 × 0.9 = 14,965 W (about 15 kW, roughly 20 HP). Apparent power = √3 × 480 × 20 = 16,627 VA.

Example 4 — Low-voltage DC: A 12 V LED strip draws 2.5 A. Power = 12 × 2.5 = 30 W. No power factor applies because the supply is DC.

On AC circuits there are three kinds of power, and the volts-to-watts conversion depends on which one you want:

• Real power (watts, W) — the power that actually does work: heat, light, torque. Equals V × A × PF.
• Apparent power (volt-amps, VA) — the raw product of voltage and current, V × A, ignoring phase. This is what transformers and wiring must be sized for.
• Reactive power (volt-amps reactive, VAR) — power that oscillates between source and load without doing net work, caused by inductance or capacitance.

Power factor is the ratio of real to apparent power: PF = W ÷ VA. A power factor of 1.0 means all supplied power does work (resistive load). A power factor of 0.8 means only 80% is useful; the rest circulates as reactive power. Utilities penalize large customers for poor power factor because reactive current still heats conductors and loads transformers.

The calculator shows both real power (W) and apparent power (VA) so you can see the gap. To learn why the √3 factor appears in three-phase, and how phase angle relates to power factor, read Ohm's law explained and the 3-phase power calculator.

Commercial and industrial equipment often runs on three-phase power, which delivers more power with less conductor than single-phase. When converting volts to watts for three-phase, the formula gains the √3 factor:

The key detail is that V is the line-to-line voltage (e.g., 208 V, 480 V, or 600 V) and A is the line current. The √3 (≈ 1.732) arises because the three phases peak 120° apart, so the combined power is not simply three times the single-phase value using line voltage.

For example, a 208 V three-phase load drawing 30 A at PF 0.85 delivers √3 × 208 × 30 × 0.85 = 9,190 W ≈ 9.2 kW. Selecting the "Three-phase" option in the calculator applies this automatically. For deeper three-phase analysis including kVA, kVAR, and line-versus-phase distinctions, use the dedicated 3-phase power calculator, and to convert three-phase amperage into kilowatts, the amps to kW calculator.

1. Enter the voltage. Use the supply voltage — nominal (120 V, 240 V, 480 V) or measured. For three-phase, enter the line-to-line voltage.
2. Enter the current in amps. Use rated or clamp-meter-measured RMS current per line.
3. Set the power factor. Use 1.0 for DC and resistive loads (heaters, incandescent lamps). Use 0.8–0.9 for typical motors, or the nameplate PF if listed.
4. Choose the system type. Select DC/single-phase for standard circuits, or three-phase to apply the √3 multiplier.

The calculator returns real power in watts and kilowatts, plus apparent power in VA and kVA. Compare the watt and VA figures to gauge how much reactive power your load draws.

Converting volts and amps to watts underpins nearly every power-sizing decision:

Generator and inverter sizing. Generators are rated in watts (and kW) but also in VA. Knowing your load's voltage, current, and power factor tells you both the real watts and the apparent VA the generator must supply — critical because a poor power factor forces you to buy a larger unit.

Electrical service and breaker sizing. Panels and breakers are rated in amps at a given voltage. Converting to watts shows the true power available: a 100 A, 240 V single-phase service can deliver up to 24,000 VA before overload.

Solar and battery systems. Inverter output is specified in watts. Multiplying the AC output voltage by current confirms the delivered power, and the VA figure helps size the inverter for reactive loads like well pumps and compressors.

Motor and HVAC engineering. Three-phase motors list voltage, full-load amps, and power factor. The √3 formula converts these into shaft-relevant input watts, which pairs with the HP to watts calculator to relate electrical input to mechanical output.

UPS and data-center provisioning. Uninterruptible power supplies are rated in both watts and VA, and the gap between them is set by the load's power factor. Modern IT equipment runs near unity power factor, so a 3,000 VA UPS may deliver close to 3,000 W, whereas older gear at 0.7 PF would cap the same unit near 2,100 W. Converting your equipment's voltage and current into both watts and VA ensures the UPS is sized for the real load, not just the apparent one, with headroom for growth and startup surges.

One of the most practical uses of volts-to-watts conversion is figuring out how much power a given circuit can safely deliver. Breakers and outlets are rated in amps at a nominal voltage, and converting that to watts tells you how many devices you can run before tripping the breaker.

The electrical code limits continuous loads to 80% of the breaker rating. So a 15 A, 120 V circuit has a raw capacity of 120 × 15 = 1,800 W, but a continuous-load ceiling of 120 × 15 × 0.8 = 1,440 W. A 20 A, 120 V circuit provides 2,400 W raw and 1,920 W continuous. Step up to 240 V and the same amperage doubles the wattage: a 30 A, 240 V dryer circuit delivers 7,200 W raw and 5,760 W continuous. This is exactly why high-power appliances move to 240 V — it halves the current for the same power, allowing thinner conductors and smaller breakers.

The multiplier from amps to watts is simply the voltage. That is why a whole-house service is described both ways: a 200 A, 240 V split-phase service can theoretically supply 240 × 200 = 48,000 W (48 kW) of single-phase power, though real homes rarely approach that continuously. For three-phase services, the √3 factor applies, and you should use the 3-phase power calculator and the amps to kW calculator to convert service amperage into available kilowatts.

When you plan which devices share a circuit, add up their watts and confirm the total stays under the 80% continuous limit. If you only know each device's amperage, multiply by the circuit voltage first. Remember that motor-driven appliances draw a brief inrush surge several times their running watts, so leave headroom on circuits feeding refrigerators, air conditioners, pumps, and power tools.

• Forgetting power factor on AC. Multiplying only V × A gives apparent power (VA), not real watts. Include PF for motors and electronics.
• Omitting √3 on three-phase. Using single-phase math on a three-phase load understates power by 42%.
• Using phase voltage instead of line voltage. The three-phase formula expects line-to-line voltage; mixing it with phase voltage produces wrong results.
• Confusing VA with watts. They are equal only when power factor is 1.0. For inductive loads, watts are always less than VA.
• Entering peak instead of RMS values. AC formulas use RMS voltage and current, not peak.

For related conversions, use the watts to volts calculator, the watts to amps calculator, and Ohm's law explained.