Electrical Converter
Electrical converter solving Ohm's law for any two of volts, amps, watts and ohms, and it shows the power factor as its own input instead of assuming it's 1.
Most used electrical tools
Watts to Amps
DC, single phase and three phase AC, with power factor as its own input.
Amps to Watts
The same calculation reversed, sharing identical logic.
Watts to Horsepower
Mechanical, metric and electrical hp kept separate.
Solve for any one value
Enter two values. Volts and amps must not be zero.
Enter any two, get the other two. These relationships assume a DC or purely resistive AC circuit, where the power factor is 1. For motors and other reactive AC loads, use the watts to amps converter, which exposes power factor as an input.
Reference only. Circuit, breaker and conductor sizing must follow the electrical code that applies where you are, and should be verified by a qualified electrician.
Every electrical converter on this site
Reference table
| Relationship | Formula | Note |
|---|---|---|
| Power from voltage and current | W = V × A | DC or resistive AC only |
| Current from power and voltage | A = W ÷ V | The most common household case |
| Resistance from voltage and current | Ω = V ÷ A | Ohm's law |
| Power from current and resistance | W = A² × Ω | Useful for heating elements |
| Power from voltage and resistance | W = V² ÷ Ω | Same, rearranged |
Power factor, and when these formulas stop working
Everything above assumes power factor 1, which holds for DC and for purely resistive AC loads such as heaters and incandescent bulbs. Motors, transformers and many electronic supplies draw current out of phase with the voltage, so the actual current is higher than W divided by V suggests.
That is why the dedicated watts to amps and amps to watts converters expose power factor as a visible input rather than assuming a value.
Watts, horsepower and motor ratings
Motor nameplates often carry a horsepower rating alongside a watt figure. Electrical horsepower is defined as exactly 746 watts for precisely this reason, though mechanical and metric horsepower differ slightly. The watts to horsepower converter keeps the three apart.
Common questions
How do I calculate amps from watts?
Divide the watts by the volts. A 1,200 watt appliance on a 120 volt circuit draws 10 amps. For an AC load with a power factor below 1, divide by the volts multiplied by the power factor.
What is Ohm's law?
Voltage equals current multiplied by resistance, written V = I × R. Combined with the power relationship W = V × A, it lets you find any two of the four quantities from the other two.
Why do I need two values?
Because the four quantities are linked by two equations. One value on its own doesn't determine the others, which is why this tool asks for a pair.
Does this work for three phase?
No. Three phase adds a factor of the square root of three, which the watts to amps converter handles with a circuit type selector.
Sources
- NIST Guide to the SI, Appendix B: Conversion Factors. National Institute of Standards and Technology. Source for every conversion factor on this page, and for which factors are exact rather than rounded.