Watts to Volts Calculator

To convert watts to volts, divide the power in watts by the current in amps: V = W ÷ A. For example, 100 watts flowing at 5 amps requires 100 ÷ 5 = 20 volts. This works because electrical power is the product of voltage and current (P = V × I), so voltage is simply power divided by current. The calculator above does this instantly and also reports the equivalent kilowatts.

You must know the current to convert watts to volts — watts alone are not enough, because the same 100 watts could be 20 V at 5 A, 100 V at 1 A, or 10 V at 10 A. Power tells you the rate of energy use, while voltage and current are two independent factors whose product equals that power. Once any two of the three quantities are known, the third follows directly.

The conversion starts from the fundamental DC power equation and rearranges it to isolate voltage:

This is a direct algebraic rearrangement of P = V × I, one of the most important relationships in electrical engineering. Dividing both sides by current (I) leaves voltage alone on one side:

• Power (P) is measured in watts (W) and represents energy consumed or delivered per second.
• Voltage (V) is measured in volts and represents electrical "pressure" or potential difference.
• Current (I) is measured in amperes (A) and represents the flow rate of electric charge.

If your power is given in kilowatts, first multiply by 1,000 to convert to watts (1 kW = 1,000 W), then divide by current. To go the other direction and find power from voltage and current, use the volts to watts calculator. To solve for current instead of voltage, use the watts to amps calculator.

These examples show the conversion across common scenarios, with the arithmetic fully shown.

Example 1 — Small DC load: A device consumes 100 W and draws 5 A. Voltage = 100 ÷ 5 = 20 V. This matches a typical 24 V nominal battery system operating under partial load.

Example 2 — Household appliance: A 1,200 W hair dryer draws 10 A. Voltage = 1,200 ÷ 10 = 120 V, exactly the North American residential standard. This confirms why a 120 V circuit at 10 A delivers up to 1,200 W.

Example 3 — Kilowatt-scale load: A 3 kW water heater element draws 12.5 A. Convert kilowatts to watts first: 3 kW = 3,000 W. Voltage = 3,000 ÷ 12.5 = 240 V, the standard for a North American 240 V appliance circuit.

Example 4 — Low-current electronics: A 60 W soldering iron draws 0.5 A. Voltage = 60 ÷ 0.5 = 120 V. Notice that halving the current doubles the required voltage for the same power — voltage and current trade off inversely at constant power.

On DC circuits the conversion V = W ÷ A is exact. On alternating current (AC) circuits, there is a subtlety called power factor (PF) that you must understand to avoid a common error.

AC loads with motors, transformers, or electronic supplies draw current that is partly out of phase with the voltage. The true power (watts) that actually does work is related to voltage and current by:

Rearranged for voltage, this becomes V = W ÷ (A × PF). If the watt figure you enter is true power measured by a wattmeter, and the amps figure is the actual RMS current, then the correct voltage is W ÷ (A × PF). For a purely resistive load — heaters, incandescent bulbs, kettles — power factor equals 1.0, so V = W ÷ A holds directly.

Typical power-factor values: incandescent and resistive heating ≈ 1.0; LED lighting 0.9–0.95; induction motors 0.7–0.9 under load; switch-mode supplies without correction 0.5–0.6. When in doubt on a motor or electronic load, factor power factor into the current side of the equation. For a full treatment, see Ohm's law explained and the watts to amps calculator.

Larger loads are often rated in kilowatts (kW) rather than watts. One kilowatt equals 1,000 watts, so the conversion is straightforward:

For example, a 7.2 kW EV charger drawing 30 A operates at 7,200 ÷ 30 = 240 V. A 5 kW off-grid inverter feeding a 240 V panel supplies 5,000 ÷ 240 = 20.8 A. The calculator above accepts watts; simply multiply any kW figure by 1,000 before entering, or read the kilowatt output to move the other direction.

This kW relationship connects to broader system sizing. To convert amps directly to kilowatts for a service panel, use the amps to kW calculator. For three-phase equipment where line voltage and phase relationships change the math, use the 3-phase power calculator, which introduces the √3 factor for balanced three-phase systems.

1. Enter the power in watts. Read it from the device nameplate, spec sheet, or a plug-in power meter. If the rating is in kilowatts, multiply by 1,000 first (2.4 kW = 2,400 W).
2. Enter the current in amps. Use the measured or rated RMS current. A clamp meter gives the most accurate real-world figure.
3. Read the voltage result. The primary output is volts; the calculator also shows equivalent kilowatts and the resistive-case resistance.
4. Account for power factor on AC. If your load is a motor or electronic supply and you entered apparent VA rather than true watts, divide the current by the power factor for an accurate voltage.

The result updates live as you type. Use it to verify a circuit's operating voltage, size components, or double-check a nameplate by cross-referencing all three quantities.

Converting watts to volts is a routine step in several real-world tasks:

Solar and battery systems. When you know a panel's watt rating and its operating current at maximum power point, dividing gives the maximum-power voltage (Vmp) — useful for matching panels to a charge controller. Battery banks are rated in amp-hours and volts, and loads in watts, so this conversion links the two.

Circuit design and troubleshooting. If a component is dissipating a known number of watts and you measure the current through it, the voltage drop across it follows immediately. This helps locate unexpected resistance or verify that a supply is delivering the correct rail voltage.

Appliance and HVAC verification. Nameplates list watts (or kW) and sometimes amps. Confirming that W ÷ A yields the expected supply voltage (120 V, 208 V, 240 V, 277 V, or 480 V) is a fast sanity check that a unit is wired for the correct service.

Automotive and DC electronics. A 12 V or 24 V accessory rated in watts reveals its operating voltage when you know the fuse-rated current, helping confirm compatibility before installation.

LED and lighting design. LED drivers are frequently specified by wattage and output current. Dividing watts by the rated drive current gives the forward voltage the string will sit at, which must match the driver's voltage window. A 24 W LED strip rated at 2 A, for instance, operates near 12 V — confirming it belongs on a 12 V supply rather than 24 V. Getting this relationship right prevents flicker, premature failure, and driver mismatch.

The voltage you calculate should usually land on a recognized standard. If it does not, either your current figure is off or the load is designed for a different region or service. Knowing the standard voltages helps you sanity-check every watts-to-volts result.

In North America, residential service is nominally 120 V for general outlets and lighting, and 240 V (split-phase) for large appliances like dryers, ranges, and water heaters. Commercial buildings add 208 V and 277 V (from 208 V and 480 V wye systems) and 480 V three-phase for motors and HVAC. Europe and much of the world use 230 V single-phase and 400 V three-phase. Low-voltage DC systems cluster at 5 V (USB logic), 12 V and 24 V (automotive, RV, marine, and small solar), and 48 V (telecom and larger battery banks).

When your W ÷ A division yields, say, 118 V, that is simply a 120 V nominal circuit measured under load with some voltage drop. A result of 208 V confirms a three-phase wye leg, while 277 V points to a commercial lighting circuit. Anything wildly off — like 63 V for a device you expected to run at 120 V — usually signals that you entered apparent current on a low-power-factor load, or mixed up watts and volt-amps. Treat the standard voltages as guardrails: the arithmetic is exact, but real supplies sag a few percent under load, and nameplate voltages are nominal targets, not guarantees.

Voltage also matters for safety classification. Circuits at or below 50 V are generally considered low-voltage and lower-risk, which is why 12 V and 24 V systems dominate DIY solar and automotive work. Above that, proper insulation, conductor sizing, and code compliance become critical. Whenever a watts-to-volts result crosses into a higher voltage class, revisit wire gauge and protection with the watts to amps calculator and confirm the current side of the equation.

• Dividing by zero current. Voltage is undefined when current is zero — you need a real current value to solve for volts.
• Mixing watts and kilowatts. Always convert kW to W (×1,000) before dividing, or the voltage will be off by a factor of 1,000.
• Ignoring power factor on motors. Using true watts with RMS current on a low-PF motor overstates voltage unless you include the power factor.
• Confusing apparent power (VA) with real power (W). On AC, VA = V × A while W = V × A × PF. Know which figure your nameplate lists.
• Assuming voltage is fixed. Supply voltage sags under heavy load; a nameplate voltage is nominal, not a guarantee of the instantaneous value.

For the reverse conversions and related power math, explore the volts to watts calculator, the watts to amps calculator, and Ohm's law explained.