Ohm's Law Calculator
Free online Ohm's Law calculator. Enter any two of voltage, current, resistance, or power and instantly get the remaining values with step-by-step derivations. Covers all six input combinations using V = I × R and P = V × I. 100% client-side.
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What is Ohm's Law Calculator?
The Ohm's Law Calculator is a free, browser-based tool that solves for any two unknown values among voltage (V), current (I), resistance (R), and power (P). Enter any two known quantities and the remaining two are derived instantly using Ohm's Law (V = I × R) and the power equation (P = V × I). The tool covers all six input combinations, shows the step-by-step derivation with substituted numbers, and displays a full formula reference. Everything runs locally in your browser — no signup, no server, and no data leaves your device.
Key Benefits
- Solve for any two unknowns without manually rearranging formulas
- Step-by-step derivation shows exactly how each result was calculated
- Handles all six input pairs (V+I, V+R, V+P, I+R, I+P, R+P)
- Smart number formatting with scientific notation for extreme values
- 100% client-side and offline — your electrical values never leave your device
Common Use Cases
- •Calculate current-limiting resistor values for LEDs, sensors, and microcontroller circuits
- •Determine power dissipation to select correctly rated resistors and components
- •Estimate battery life and current draw for portable and IoT devices
- •Verify circuit calculations for homework, lab work, or electronics courses
- •Quickly convert between voltage, current, resistance, and power when troubleshooting
How to Use the Ohm's Law Calculator
- Enter two known values: Type any two of voltage (V), current (I), resistance (R), or power (P). As soon as the second value is entered, the remaining two are calculated automatically.
- Read the calculated results: The two unknown fields are filled in automatically and highlighted as "Calculated". You cannot edit a calculated field directly — clear one of your inputs to change the combination.
- Review the step-by-step derivation: Below the inputs, the tool shows the exact formula with your numbers substituted in, so you can verify how each result was obtained.
- Copy the result summary: Click Copy to save the complete summary (V, I, R, and P) to your clipboard, or use Clear to start a new calculation from scratch.
Key Features
- Enter any two of voltage, current, resistance, or power and the remaining two values are derived automatically in real time
- Supports all six input combinations (V+I, V+R, V+P, I+R, I+P, R+P) with correct rearrangement of Ohm’s Law and the power equation
- Step-by-step derivation shows the substituted numbers for each formula, not just the final answer
- Smart number formatting that switches to scientific notation for very large or very small results
- Complete formula reference covering every arrangement of V = I × R and P = V × I always visible on screen
- 100% client-side and offline — no signup, no server, and your electrical values never leave your device