Convert voltage and current to real power for DC, single-phase AC, or balanced three-phase AC.
Table of contents
How to use our Volts to Watts Calculator
- Choose the Circuit type: DC, AC, single phase, or AC, three phase.
- Enter Voltage (V) and Current (A) from the label, meter, or supply.
- For AC, enter Power factor (0 to 1); for three-phase AC, also choose Three-phase voltage entered.
- Open Advanced options only if you want a different Power unit to show or Number format.
- Use Formula used and Apparent power to sanity-check the result. If apparent power is far above Real power, the power factor is doing a lot of the change.
Definitions
Voltage (V): Electrical pressure, measured in volts. It is the V number on many labels and meters.
Current (A): Electric charge flow, measured in amps. A higher current usually means more power for the same voltage.
Real power: Usable power in watts or kilowatts after power factor is applied for AC.
Apparent power: Voltage times current before power factor. It is measured in volt-amps, or VA.
Power factor (0 to 1): The part of AC apparent power that becomes real power. A value of 1 means all apparent power is counted as real power in this calculator.
Line-to-line voltage: Three-phase voltage measured between two line wires.
Line-to-neutral voltage: Three-phase voltage measured from one line wire to neutral.
Balanced three-phase AC: A three-phase load where the phases are treated as evenly loaded for the total power formula.
Common mistakes and quick fixes
Mistake: Leaving Circuit type on DC for a wall outlet or motor load.
Fix: Change Circuit type to AC, single phase or AC, three phase so Power factor (0 to 1) is used.
Mistake: Entering a percent like 90 in Power factor (0 to 1).
Fix: Enter 0.90 instead, because the calculator expects a value from 0 to 1.
Mistake: Using line-to-neutral voltage while Three-phase voltage entered is set to Line-to-line voltage.
Fix: Match Three-phase voltage entered to how Voltage (V) was measured.
Mistake: Reading Apparent power as the same thing as Real power for AC.
Fix: Use Real power for watts. Use Apparent power only as the volt-amp check before power factor.
Mistake: Comparing a kW main answer with a W label and thinking the result is off by 1000.
Fix: Check Real power in watts, or set Power unit to show to Watts (W).
Limitations & Key Assumptions / Boundary Conditions
- This calculator uses voltage and current magnitudes. It does not model the direction of power flow.
- For AC, use RMS voltage and RMS current values. Peak voltage or peak current will give the wrong watts.
- Power factor is entered by the user. The calculator does not estimate it from appliance type, motor size, or utility data.
- Three-phase results assume a balanced load. Unbalanced three-phase systems need per-phase measurements.
- For three-phase AC, the selected Three-phase voltage entered must match the measurement. Line-to-line and line-to-neutral use different formulas.
- DC apparent power is shown as matching watts in this simplified calculator.
- Real equipment labels can include starting current, efficiency, duty cycle, or safety margins that this calculator does not include.
Methodology
How the calculator chooses the formula
The calculator first reads Circuit type. It checks comma or space grouping in Voltage (V) and Current (A), removes valid grouping separators, then checks that voltage is greater than 0 and current is 0 or more. For DC, power factor is not read. For AC, Power factor (0 to 1) must be a number from 0 to 1.
DC: P_W = V * I
Single-phase AC: P_W = V_rms * I_rms * PF
Three-phase AC, line-to-line: P_W = sqrt(3) * V_LL * I_L * PF
Three-phase AC, line-to-neutral: P_W = 3 * V_LN * I_L * PF
For balanced three-phase AC with line-to-line voltage, the total real-power formula uses the square root of 3, line voltage, line current, and power factor [4]. If Three-phase voltage entered is line-to-neutral, the calculator uses 3 times line-to-neutral voltage instead.
Apparent power and display units
Apparent power is calculated before power factor. In AC work, this helps show why volt-amps can be higher than watts when power factor is below 1.
DC or single-phase AC: S_VA = V * I
Three-phase AC: S_VA = sqrt(3) * V_LL * I_L, or S_VA = 3 * V_LN * I_L
P_kW = P_W / 1000
Internal math stays in watts and volt-amps. The Power unit to show option only changes how the answer is displayed. Auto uses W for smaller real-power results and kW for larger ones.
Mini-example
For a single-phase AC load with Voltage (V) = 120, Current (A) = 10, and Power factor (0 to 1) = 0.80, the real power is 120 * 10 * 0.80 = 960 W. The apparent power is 120 * 10 = 1200 VA, so the 0.80 power factor reduces the usable watt result compared with the volt-amp value.