What is it?
The Ohm’s Law Calculator finds voltage, current, resistance or power. Fill in any two of them and it works out the other two.
Who is it for?
Electronics hobbyists, students, electricians and anyone choosing resistors, fuses or wires.
How to use it
Fill in any two values; the other two are worked out. Leave the others empty. The answer appears as you type; there is no Calculate button. Tap Copy result to copy it, or Share on WhatsApp to send it.
The formulas
Ohm’s law: V = I × R, and power P = V × I. From these: I = V ÷ R, R = V ÷ I, P = I² × R = V² ÷ R.
Examples
- An LED on 5 V needing 20 mA with 2 V across it: the resistor drops 3 V, so R = 3 ÷ 0.02 = 150 Ω (use the next standard value up).
- A 2,000 W heater on 230 V draws 2000 ÷ 230 ≈ 8.7 A.
Units
- Enter current in amperes: 20 mA = 0.02 A. Resistance in ohms: 4.7 kΩ = 4700.
- For AC appliances with motors, real power also depends on the power factor; use the Electrical Power Calculator.
Electrical work can kill. Use these numbers for planning and learning; have a licensed electrician do and check any wiring, following your local wiring rules.
Errors and how to fix them
- “Fill in exactly two of the four boxes and leave the other two empty”
Open the tool: Ohm's Law Calculator
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