Solve voltage, current, resistance and power from any two values in your browser. Your circuit numbers stay on your device.
Ohm’s Law Calculator Online
Solve voltage, current, resistance and power from any two values in your browser. Your circuit numbers stay on your device.
The Ohm’s Law Calculator runs entirely in your browser. The voltage, current, resistance and power values you enter never leave your device and are not uploaded to ArrayKit.
The Ohm’s Law Calculator solves voltage, current, resistance and power the moment you enter any two of the four values. Type in voltage and resistance and it derives current and power with V = I × R and P = V × I; enter current and power instead and it works backward to find voltage and resistance. It is built for hobbyists sizing a resistor, students checking homework, and electricians or makers sanity-checking a circuit before they build it. Every field updates instantly as you type, and a copy button grabs a plain-text summary of all four values for your notes. Everything runs locally in your browser — nothing about your circuit is uploaded anywhere. Results are estimates for ideal resistive components, so verify real-world wiring with a multimeter.
Features
Solves for voltage, current, resistance and power from any two known values
Applies V = I × R and P = V × I automatically, including the derived power forms
Live results update as you type — no submit button needed
Marks which two values were computed versus the two you entered
Copy button grabs a plain-text summary of the full V/I/R/P result set
Clear errors for contradictory pairs and for numbers it can't read unambiguously
Works for AC and DC resistive-circuit estimates alike
Runs entirely in your browser with no circuit data sent anywhere
How to use the Ohm’s Law Calculator
Enter any two of voltage, current, resistance or power
Leave the other two fields blank
Read the computed values in the result list
Copy the summary or adjust a value to explore a different scenario
Example
Input
V=12, R=4
Output
I=3 A · P=36 W
Ohm’s Law: I = V ÷ R = 12 ÷ 4 = 3 A, and P = V × I = 12 × 3 = 36 W.
Common errors & troubleshooting
Only one value is filled in and nothing calculates. — Ohm’s Law needs two known quantities to solve for the other two — fill in a second field such as current or power.
Result shows a 'cannot determine' error with a 0 entered. — A 0 A current or 0 Ω resistance paired with a nonzero voltage or power is contradictory — check for a typo or try a different pair of values.
A result is a thousand times too big or too small. — Double-check units: voltage in volts, current in amps, resistance in ohms and power in watts. Type 0.02 for 20 mA and 4700 for 4.7 kΩ; unit letters and prefixes are rejected, not guessed.
A negative resistance or power, or a voltage and current of opposite signs, is rejected. — A resistor can't have negative resistance or power, and the voltage across it shares a sign with the current through it. Enter positive magnitudes, or make both voltage and current negative.
Typing a decimal comma, such as 0,02. — A comma followed by one or two digits, or after a leading 0, is read as a decimal comma, so 0,02 is 0.02. In 1,000 and 1,000.5 the comma separates thousands, and anything ambiguous, such as 1.000,5 or 1,2,3, shows an error instead of a guess.
Frequently asked questions
What is the Ohm’s Law Calculator used for?
It solves the four core electrical quantities — voltage, current, resistance and power — from any two of them, using V = I × R and P = V × I so you don't have to rearrange the formulas by hand.
Which two values does the Ohm’s Law Calculator need?
Any two of voltage, current, resistance or power. Common pairs are voltage and resistance, or current and power — the calculator figures out the remaining two automatically. If you fill in more, it solves from the first pair in the order voltage, current, resistance, power and warns when the others don't match.
How does the calculator find power if I only enter voltage and current?
It multiplies them directly with P = V × I, then still reports resistance using R = V ÷ I so all four values are shown together.
Can the Ohm’s Law Calculator handle resistance and power as the two inputs?
Yes. From resistance and power it solves current with I = √(P ÷ R), then derives voltage with V = I × R.
Is the Ohm’s Law Calculator accurate for real circuits?
It gives an exact result for ideal, purely resistive components under the entered conditions. Real components have tolerances and temperature effects, so treat the output as an estimate and verify with a multimeter before relying on it.
Does the Ohm’s Law Calculator send my values anywhere?
No. All the math runs locally in your browser. The voltage, current, resistance and power you type are never uploaded to ArrayKit.
Related tools
Voltage Drop Calculator — Estimate voltage drop over a wire run from gauge, length and current.