Electronics
Ohm's Law Calculator
Fill in any two values. The other two, the circuit and the formula wheel update as you type.
You can use prefixes: 4.7k, 4k7, 20m (milli), 100u (micro), 2M2. The two most recent fields you typed in are the inputs (outlined).
Your circuit
Formula wheel
The highlighted formulas are the ones used for your two values.
About this tool
Ohm's law
V = I ร R: the voltage across a resistor equals the current through it times its resistance. Combine it with the power law P = V ร I and you can find any two of the four quantities from the other two, which is what the twelve formulas in the wheel do.
Check your resistor's power rating
Common through-hole resistors are rated ยผ W, and small SMD parts โ W or less. Pick a part rated at least twice the power you calculate, so it runs cool.