Watts to Volts Calculator
Enter watts and amps to work out the voltage, for DC and AC circuits.
What this tool does
A watts to volts calculator works out the supply voltage when you know the power and the current. On DC, volts = watts ÷ amps. On AC single-phase, volts = watts ÷ (amps × power factor). Enter the power in watts, the current in amps and, for AC, the power factor, and the voltage appears in volts.
Calculates voltage when power and current are known, with power factor for AC circuits.
Uses V = P ÷ I for DC and V = P ÷ (I × PF) for AC single-phase, so the two cases are never mixed up.
Shows the formula used with the result, so the answer can be checked by hand.
Rejects a zero or missing current, which would otherwise produce an infinite or meaningless voltage.
How to use it
- Choose whether the circuit is DC or AC single-phase.
- Enter the power in watts.
- Enter the current in amps.
- For AC, enter the power factor between 0 and 1 (1.0 for resistive loads).
- Read the voltage in volts, and the formula used to get it.
Why use this calculator
Calculates voltage when power and current are known, with power factor for AC circuits. Appliances are labelled in watts, cables and fuses are rated in amps, and supplies are quoted in volts - when two of the three are given, the third follows from one division. It is the calculation behind choosing a transformer, checking a battery's output, or confirming that a supply really is what a device expects.
Why we built it
We built the watts to volts calculator because the reverse calculation gets far more traffic and the pair should exist together. The volts to watts calculator runs power from voltage and current, the watts to amps converter and the amps to watts converter cover current, and the Ohms Law calculator solves any pair of voltage, current, resistance and power.
If your task goes further, try the Power Factor Calculator to find the power factor from measured kW and kVA, and the kW to kVA converter when the power is quoted as apparent rather than real power.
Who this tool is for
- Technicians checking what voltage a load needs for a given power draw
- DIYers matching a device to a battery, supply or generator
- Students verifying a circuit calculation
- Anyone who knows watts and amps and needs the volts
When to use it
- Working out the voltage a power supply must deliver for a load.
- Checking whether a 12 V, 24 V or 48 V battery system suits a device.
- Confirming a transformer or inverter output for a stated wattage.
- Reverse-engineering a rating plate that lists watts and amps only.
How it is calculated
DC: voltage = watts ÷ amps (V = P ÷ I). AC single-phase: voltage = watts ÷ (amps × power factor), or V = P ÷ (I × PF), because watts already include the power factor. If the figure you have is in volt-amps rather than watts, divide by the amps directly - apparent power and current are in phase by definition. Three-phase uses the square root of three as well: V = P ÷ (√3 × I × PF).
Worked example: a 1,500 W load drawing 10 A on DC sits on a 1,500 ÷ 10 = 150 V supply. The same 1,500 W and 10 A on AC with a power factor of 0.85 needs 1,500 ÷ (10 × 0.85) = 176.5 V. Ignoring the power factor would suggest 150 V, and a supply built to that figure would be about 15% too low for the load.
Power factor only belongs in the denominator when the power is real power in watts. If your figure is in kVA, multiply by 1,000 and divide by the current alone.
What you enter, and what you get back
| Item | Details |
|---|---|
| Circuit type | DC or AC single-phase. |
| Power | The power in watts. |
| Current | The current in amps. |
| Power factor | 0 to 1, required for AC. |
| Result | The voltage in volts, with the formula used. |
A worked example
A worked example you can repeat in the calculator above. Change any input and the result updates from the same formula.
| Input | Value |
|---|---|
| Circuit type | AC single-phase |
| Power | 1,500 W |
| Current | 10 A |
| Power factor | 0.85 |
With those inputs, the calculator returns:
- Voltage: 176.5 V
- Formula used: V = P ÷ (I × PF) = 1,500 ÷ (10 × 0.85)
- Apparent power: 1,500 ÷ 0.85 = 1,765 VA
- Reactive power: about 930 var (√ of 1,765² − 1,500²)
Finding the voltage of a real appliance
Most devices carry a rating plate or a moulded label giving the supply voltage directly - 120 V, 230 V, or a range such as 100-240 V, which means an internal switch-mode supply will accept either. When the label only gives power and current, this calculation recovers the voltage it was designed for. Battery-powered devices use the battery voltage: a car is 12 V nominal (about 12.6 V resting, 14.4 V while charging), an RV or solar bank is commonly 12 V or 24 V, and a laptop brick is usually 19 V.
Be careful with the direction of the calculation. Volts and amps together define the power a device draws; watts and amps together define the voltage it expects. If both watts and volts are known and you want the current, that is the watts to amps converter, not this one.
Appliances with motors and compressors list running power, not the higher starting surge, so a voltage calculated from the running figures says nothing about the dip the supply sees at startup.
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| Voltage looks too low | Power factor of 1 was used on an AC motor. | Enter the real power factor, typically 0.7 to 0.9. |
| Result is enormous or empty | Current is zero or was left blank. | Enter the actual current in amps. |
| Answer is in kVA, not watts | Apparent power was entered as real power. | Convert kVA to kW first, or divide kVA by amps directly. |
Assumptions and limitations
- Covers DC and AC single-phase only; three-phase needs the square root of three factor as well.
- The voltage is only as accurate as the power factor you enter - an unknown power factor is an assumption, not a measurement.
- Real supplies sag and rise under load, so the calculated voltage is the design value, not a measured one.
- An aid for estimation, not a substitute for an electrician's calculation on fixed wiring.
Frequently asked questions
How do I convert watts to volts?
Divide the power in watts by the current in amps. On DC, V = P ÷ I, so 1,500 watts at 10 amps is 150 volts. On AC single-phase, divide by the power factor too: V = P ÷ (I × PF), which gives 176.5 volts at a power factor of 0.85.
What is the difference between watts and volts?
Volts are the electrical pressure the supply provides; watts are the rate the load consumes energy. Watts combine voltage and current (watts = volts × amps on DC, times the power factor on AC), so a volt figure alone says nothing about how much power is flowing.
Why does AC need a power factor?
Inductive loads such as motors make the current lag the voltage, so some of each cycle's power returns to the supply instead of doing work. The power factor (real power ÷ apparent power, between 0 and 1) is what converts a wattage figure into the correct voltage for a given current.
How do I find the voltage of my appliance?
Read the rating plate or the label on the plug or charger - it states the supply voltage or a range such as 100-240 V. If the label only gives watts and amps, enter both here and the design voltage follows from the division.
What is a typical power factor?
Resistive loads such as heaters and incandescent bulbs are 1.0. Motors and compressors run at 0.7 to 0.95, and switch-mode power supplies sit around 0.6 to 0.9. Use 0.85 as a default for a mixed AC load when the real value is unknown.
Is this the same as my electricity bill?
No. Your bill measures energy in kilowatt-hours over a billing period, not voltage. The volts here are the supply your equipment sees - nominally about 120 V in North America and 230 V in the UK, Europe, Australia and South Africa.