Ohm's Law Calculator (V, I, R, P)

Enter any two of voltage, current, resistance and power — solve the rest.

Fill any two. Leave the others blank.

Formulas

V = I · R  (Ohm's law)
P = V · I
Derived: P = I²·R, P = V²/R

How to use

  1. Type any two known values into their fields.
  2. Leave the others empty.
  3. Click Calculate.

Physics behind Ohm's law

Ohm's law is the most-used rule in elementary circuit analysis. It says that the voltage across a resistor equals the current through it times its resistance. This is a linear relationship — double the voltage and the current doubles — and it's valid as long as the resistor is ohmic (metals at normal temperatures). Combined with P = V·I, it lets you calculate every relevant quantity in a simple DC circuit.

Worked example

V = 12 V, R = 6 Ω

I = V/R = 12/6 = 2 A
P = V·I = 12·2 = 24 W

Related tools

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FAQs

What is Ohm's law?

V = I·R — the voltage across an ohmic conductor equals current times resistance.

How do I compute power?

P = V·I, or equivalently P = I²R, P = V²/R.

Do all conductors obey Ohm's law?

No — only ohmic devices such as resistors.