Ohm's Law (V, I, R, P) Calculator
Ohm's law calculator: enter any two of voltage, current, resistance and power and get the rest. Formula, worked example and typical values.
Try your own numbers
Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
Open in the calculator with these values
Formula
Worked example
| Input | Value |
|---|---|
| Voltage | 230 V |
| Current | 5 A |
- R = V / I = 230 / 5 = 46 Ω
- P = V × I = 1,150 W
Typical values
| Current (A) | Resistance (Ω) | Power (W) |
|---|---|---|
| 0.5 | 460 | 115 |
| 1 | 230 | 230 |
| 2 | 115 | 460 |
| 5 | 46 | 1,150 |
| 10 | 23 | 2,300 |
| 20 | 11.5 | 4,600 |
Other inputs are the same as in the worked example above.
Assumptions
- Steady DC or purely resistive AC load
- AC values are RMS
- Power factor is 1; for a reactive load use the power, voltage and current calculator
Exactly two values are needed. If three or four are entered the result could contradict itself, so the calculator asks for two only.
Frequently asked questions
How is Ohm's Law (V, I, R, P) calculated?
V = I × R; P = V × I; P = I² × R; P = V² / R. Worked example: Voltage 230 V, current 5 A gives Resistance: 46 Ω · Power: 1,150 W.
What do I need to enter?
Enter voltage, current, resistance and power. Leave blank the value you want to find, and the form solves for it. Change the unit of a value with its selector and the result stays the same.
Why can I only enter two values?
Any two of voltage, current, resistance and power fix the other two. With three or four entered the values could contradict each other, so the calculator asks for two.
Does this work for AC circuits?
Only for resistive loads, using RMS values, where the power factor is 1. A load with reactance needs impedance and phase angle, and the power depends on the power factor; use the AC Ohm's law (phasors) calculator in Elecmetric, which takes magnitude and angle for voltage, current and impedance and returns the power triangle.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. Check design values against the standard and the equipment data you work to.
Related
Next steps in a design: Ohm's LawVolts to WattsAmps to VoltsAC Ohm's Law
Also see: Watts, Volts, Amps and Ohms Amps to Ohms Ohms to Amps Volts to Ohms Power
Formula guides: Ohm’s Law Formulas and Power WheelResistor Formulas: Series, Parallel, Divider
All 78 conversionsWatts, Volts, Amps, Ohms (any two) in ElecmetricAC Ohm's law (phasors) in Elecmetric