Calculator
Ohm’s Law Calculator
Enter any two of voltage (V), current (I), resistance (R), or power (W) and this calculator solves the other two instantly using the Ohm’s law wheel, and shows the exact formula behind each answer. Free, no signup.
Free
Enter any two valuesFill any two of voltage, current, resistance, or power, the other two solve instantly. Enter a third and the oldest is cleared.
Examples
VoltageGiven
120 VCurrentGiven
5 AResistanceSolved
24 ΩPowerSolved
600 WFormulas used
R = V ÷ IP = V × I
Ohm's Law formula wheel
Every result comes from these twelve formulas, any two of the four quantities solve the rest.
| Voltage (V) | V = I × R · V = P ÷ I · V = √(P × R) |
| Current (I) | I = V ÷ R · I = P ÷ V · I = √(P ÷ R) |
| Resistance (R) | R = V ÷ I · R = V² ÷ P · R = P ÷ I² |
| Power (P) | P = V × I · P = I² × R · P = V² ÷ R |
What you'll get
Enter any two values
Type any two of voltage, current, resistance, or power. The calculator detects which two you know, enter a third and it clears the oldest so there is always a solvable pair.
See the other two solved
The remaining two quantities are calculated instantly and marked “Solved,” with the specific formula used shown for each, for example I = V ÷ R and P = V² ÷ R.
Check your work against the wheel
Open the Ohm’s law formula wheel to see all twelve equations grouped by the quantity they solve for, so you can verify or hand-calculate any combination.
How it works
- 1
Enter any two values
Type any two of voltage, current, resistance, or power. The calculator detects which two you know, enter a third and it clears the oldest so there is always a solvable pair.
- 2
See the other two solved
The remaining two quantities are calculated instantly and marked “Solved,” with the specific formula used shown for each, for example I = V ÷ R and P = V² ÷ R.
- 3
Check your work against the wheel
Open the Ohm’s law formula wheel to see all twelve equations grouped by the quantity they solve for, so you can verify or hand-calculate any combination.
How the Ohm’s law wheel works
Ohm’s law states that voltage equals current times resistance (V = I × R), and Joule’s power law adds power as the product of voltage and current (P = V × I). Combine and rearrange those two relationships and you get the twelve-formula “Ohm’s law wheel”, a set of equations that lets you solve any one of the four quantities (voltage, current, resistance, power) from any two you already know. This calculator implements the full wheel, so you never have to remember which rearrangement to use.
For example, if you know a circuit runs at 120 volts and draws 5 amps, the calculator returns 24 ohms of resistance (R = V ÷ I) and 600 watts of power (P = V × I). Know the wattage and voltage of an appliance instead? It solves current with I = P ÷ V and resistance with R = V² ÷ P. Every result shows the formula it used, making this a fast field reference for electricians and apprentices and a clear teaching aid for students. For real-world AC loads where power factor and single- or three-phase current matter, use the watts to amps calculator alongside this one.
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Ohm’s Law Calculator FAQs
Ohm’s law is V = I × R, where V is voltage in volts, I is current in amps, and R is resistance in ohms. It rearranges to I = V ÷ R and R = V ÷ I. Adding the power law P = V × I gives the full wheel, including P = I² × R, P = V² ÷ R, V = √(P × R), and I = √(P ÷ R).
Power in watts equals voltage times current: P = V × I. So a 120 V circuit drawing 5 A uses 600 watts. If you know current and resistance instead, use P = I² × R; if you know voltage and resistance, use P = V² ÷ R.
Yes. From power and resistance the calculator solves voltage with V = √(P × R) and current with I = √(P ÷ R). Enter any two of the four quantities and it handles the correct rearrangement automatically.
This tool uses the DC / resistive form of Ohm’s law, where power factor is 1. For AC circuits where power factor and single- or three-phase current change the amperage, use our watts to amps calculator, which adds the √3 three-phase factor and a power-factor input.
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