What is Ohm's law?
Ohm's law relates voltage (V), current (I), and resistance (R): V = I × R.
Ohm's Law Calculator
Use Ohm's law and the power formulas to find the missing electrical value—voltage, current, resistance, or power.
Solve an Ohm's law problem
Choose what to calculate, then enter the two known values.
About this calculator
How to use Ohm's Law Calculator, plus the formulas and logic behind the results.
Tool description
The Ohm's Law Calculator finds voltage, current, resistance, or power from two known quantities. It is useful for electronics, wiring checks, and basic circuit design.
How to use
- Select what you want to solve for.
- Enter the two known values in consistent SI units (V, A, Ω, W).
- Select Calculate to view the result and related electrical quantities when available.
Formulas & reference
V = I × RI = V ÷ RR = V ÷ IP = V × I = I² × R = V² ÷ R
Core formulas
- V = I × R
- I = V ÷ R
- R = V ÷ I
- P = V × I = I²R = V² ÷ R
Calculation logic
Each mode maps to one Ohm’s law or power identity. Division by zero is blocked. When voltage and current (or equivalent pairs) are known, related power or resistance is also reported.
Enter positive real values. Results are DC / resistive-load estimates and ignore AC reactance.
Ohm's Law Calculator FAQ
Common questions about this calculator and how to use the results.
What units should I use?
Use volts (V), amperes (A), ohms (Ω), and watts (W).
Can I find power with this tool?
Yes. Choose a power mode and enter V & I, I & R, or V & R.
Does this work for AC circuits?
It is a good estimate for resistive AC loads. Reactive circuits need impedance methods.
Why did I get an error?
Current or resistance cannot be zero when used as a divisor.
What is the difference between power modes?
Each power mode uses a different known pair: VI, IR, or VR.