Electricity Converter
Electricity Converter — runs in your browser. Inputs are not stored.
Electrical units · Ohm’s law
Enter any two to calculate the rest. (P=VI, V=IR, P=I²R …)
Enter values, then press Calculate.
How to use
- In mode, choose V·A·Ω·W relations or unit conversion. Default is Ohm’s law relations.
- In relation mode, enter two values among voltage V, current I, resistance R, and power P.
- Press Calculate to fill the other two. A prompt appears if only one value is present.
- In unit-conversion mode, pick kind (voltage, current, resistance, power) and the input unit, then enter a value.
- Reset clears the fields. Only DC simple relations are handled; AC power factor is not included.
Key concepts
Ohm’s law is V = I·R. Power is P = V·I = I²R = V²/R. Given any two of the four quantities, the others follow. Combinations differ: voltage and current give resistance and power; voltage and resistance give current and power. Division by zero is an error. Relation-mode fields are left empty or filled with numbers only. Pair priority is V·I, V·R, V·P, I·R, I·P, R·P. Switching to unit mode hides relation fields and opens scale choices.
Unit-conversion mode only changes scale: voltage V↔mV↔kV, current A↔mA↔µA, resistance Ω↔kΩ↔MΩ, power W↔mW↔kW. For horsepower and BTU use the power unit converter; for plain arithmetic use the web calculator. It is meant for DC resistive loads such as bulbs and USB adapters. Motor inrush and AC corrections such as power factor 0.8 are not included. Results appear as four lines: V, A, Ω, W.
Example
12 V and 2 A give R = 6 Ω, P = 24 W. 5 V and 10 Ω give I = 0.5 A, P = 2.5 W. In unit mode, 3.3 kΩ is 3300 Ω and 0.0033 MΩ. A 220 V 60 W bulb assumption is I ≈ 0.273 A. 9 V and 330 Ω give I ≈ 0.0273 A, P ≈ 0.246 W. In unit mode 500 mA is 0.5 A and 500000 µA. Two values are enough to ballpark an LED series resistor.
Related: Power unit converter · Web calculator
Frequently asked questions
How many values does the Ohm’s law calculator need?
At least two. The other values are found from any two filled V·A·Ω·W fields. If three or more are filled, earlier pair order is used and the third may be ignored. Leaving only two filled is safer.
How are V, A, Ω, and W related?
P=VI, V=IR, P=I²R, P=V²/R. It assumes a DC resistive load. There is no reactance or power factor. If you know only power and set voltage, current and resistance follow. 0 V is a division error.
How do I use mV/kV voltage unit conversion?
Switch mode to unit conversion, pick voltage, then choose mV or kV as the input unit. Current, resistance, and power work the same way. Microamperes suit sensor standby current; kilovolts suit intake equipment labels. Pick the kind first.
Does it calculate AC power factor?
No. There is no apparent vs real power split. Only simple DC relations and SI prefix conversion. Do not mix 220 V RMS single-phase with DC formulas. This screen is DC relations.
Which tool converts horsepower and kW only?
Use the power unit converter. Power units here are only W·mW·kW scale. Horsepower and BTU belong there; kW here is prefix conversion.
What happens on division by zero?
Combinations with current or resistance of 0 cannot be calculated. Enter values again. 0 Ω is treated as a short and fails. Use a small positive value.
Last reviewed: 2026-09-04