Loading Calculator...
Please wait a moment
Please wait a moment
Convert power (watts) to voltage using current or resistance. Calculate voltage from power consumption.
V(V) = P(W) ÷ I(A)
Voltage equals power divided by current
V(V) = √(P(W) × R(Ω))
Voltage equals square root of power times resistance
| Power | @ 1A | @ 5A | @ 10A | @ 20A |
|---|---|---|---|---|
| 100W | 100V | 20V | 10V | 5V |
| 500W | 500V | 100V | 50V | 25V |
| 1000W | 1000V | 200V | 100V | 50V |
| 1500W | 1500V | 300V | 150V | 75V |
| 2000W | 2000V | 400V | 200V | 100V |
| 5000W | 5000V | 1000V | 500V | 250V |
Converting watts to volts is the process of determining voltage from a known power value and at least one other electrical parameter – either current (amps) or resistance (ohms). Unlike simple unit conversions, watts and volts measure different physical quantities: watts measure power (the rate of energy transfer), while volts measure electrical potential difference (the force that pushes electrons through a circuit). This means you cannot convert watts to volts directly without additional information. Using Ohm's Law and the power equation, the two primary formulas are V = P ÷ I (voltage equals power divided by current) and V = √(P × R) (voltage equals the square root of power times resistance). This calculation is essential for verifying that electrical devices operate at the correct voltage, designing power supply circuits, troubleshooting voltage drops, sizing transformers, and ensuring compatibility between components in both DC and AC electrical systems.
Find the wattage of your device from the nameplate, data sheet, or by measurement. For AC devices, use the real power (watts), not the apparent power (VA). Common examples: 60W light bulb, 1500W space heater, 3000W electric dryer.
You need either the current in amps (measured with a clamp meter or ammeter) or the resistance in ohms (measured with a multimeter). For AC circuits, you may also need the power factor if working with apparent power.
If you know current: V = P ÷ I. For example, 1200W ÷ 10A = 120V. If you know resistance: V = √(P × R). For example, √(1440 × 10) = √14400 = 120V. For three-phase AC: V = P ÷ (√3 × I × PF).
Cross-check your calculated voltage against standard voltage levels (12V, 24V, 120V, 240V, 480V). If the result is not near a standard voltage, double-check your inputs. Measure with a multimeter to confirm if possible.
Knowing the voltage requirements of components is critical when designing power supplies, selecting transformers, and ensuring devices receive the correct operating voltage for reliable performance.
When diagnosing electrical faults, calculating expected voltage from known power and current helps identify voltage drops, overloaded circuits, and failing components quickly.
Utilities use higher voltages for long-distance transmission to reduce current and minimize power losses. Understanding the watts-to-volts relationship explains why transmission lines operate at hundreds of kilovolts.
| Power (W) | Current (A) | Voltage (V) | Typical Application |
|---|---|---|---|
| 60 W | 5.0 A | 12 V | Automotive accessories |
| 120 W | 5.0 A | 24 V | Industrial control systems |
| 600 W | 5.0 A | 120 V | US household outlet |
| 1200 W | 10.0 A | 120 V | Hair dryer, microwave |
| 2400 W | 10.0 A | 240 V | Electric dryer, water heater |
| 4600 W | 20.0 A | 230 V | European heavy appliance |
| 7200 W | 30.0 A | 240 V | EV Level 2 charger |
| 9600 W | 20.0 A | 480 V | Commercial three-phase motor |
A standard 60W incandescent bulb drawing 0.5A operates at 120V (60W ÷ 0.5A = 120V). The same 60W rating at 240V would draw only 0.25A. The wattage alone does not specify the voltage – you always need at least one more value.
For AC circuits, the watts to volts conversion requires considering the power factor (PF). The formula becomes V = P ÷ (I × PF) for single-phase circuits. For three-phase circuits, use V = P ÷ (√3 × I × PF). AC voltage values are typically given as RMS (root mean square) values.
Since P = V × I, for a fixed power output, increasing voltage proportionally decreases current. This is why power transmission lines use high voltages (up to 765 kV) to reduce current and minimize resistive losses (I² × R) over long distances.
North America uses 120V/240V residential and 208V/480V commercial. Europe, Asia, and most other regions use 230V/400V. Industrial three-phase systems commonly use 480V or 600V. Automotive systems use 12V DC, while telecommunications use 48V DC.
Starting with P = V × I and V = I × R, substituting I = P/V into Ohm's Law gives V = P/I. Alternatively, substituting I = V/R into the power equation gives P = V² ÷ R, which rearranges to V = √(P × R). Both formulas are mathematically equivalent expressions of the same physical relationships.