Ohm's law calculator
Current and power from voltage and resistance.
Enter your values and press Calculate. Your inputs stay in the address, so you can switch language or share the link.
Formula
I = V ÷ R P = V × I
How it works
Ohm's law says current equals voltage divided by resistance: I = V ÷ R. Electrical power is voltage times current: P = V × I.
Worked example
The same calculation with the default values:
- Voltage 12 V
- Resistance 470 Ω
- I = 12 ÷ 470 = 0.025532 A
- P = 12 × 0.025532 = 0.306383 W
Result: Current: 0.02553191 A · Current (milliamperes): 25.53191489 mA · Power: 0.30638298 W
Strictly valid only for ohmic components whose resistance is constant regardless of voltage or current - many real components (diodes, transistors, lamps at varying temperature) are non-ohmic and don't follow this relationship exactly.
Common mistakes
- Mixing up which two values are known and which is being solved for - the same three equations (I=V/R, V=IR, R=V/I) are just algebraic rearrangements of each other, so entering the wrong pair gives a meaningless answer.
- Applying Ohm's law to a non-ohmic component (diodes, some resistors at high power, most semiconductors) - it strictly holds only for components where resistance stays constant as voltage/current change.
- Ignoring that real resistors have a tolerance and can change resistance with temperature - the calculated figures assume an ideal, exact, constant resistance.
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