How to use the ohm's law calculator
The formulas
V = I × R | I = V ÷ R | R = V ÷ I | P = V × I (which also gives P = I²R and P = V²/R).
How to use it
Type any two of the four values and press Calculate. The two fields you leave blank are the ones solved for you. To start over, just clear the fields you no longer want fixed.
Remembering the triangle
Picture V on top of a triangle with I and R below it. Cover the value you want: cover V and you see I × R; cover I and you see V over R; cover R and you see V over I. Apprentices have used this picture for a century because it works.
Example
A 12 V supply feeding a load that draws 3 A: resistance is 12 ÷ 3 = 4 Ω and power is 12 × 3 = 36 W. Try it above: enter 12 in Voltage and 3 in Current, leave the rest blank.
Frequently asked questions
What is Ohm's law?
Ohm's law states that voltage equals current multiplied by resistance: V = I × R. Combined with the power formula P = V × I, any two known values reveal the other two.
Which two values should I enter?
Any pair works: volts + amps, volts + ohms, amps + watts, and so on. Leave the two fields you want solved blank.
Does Ohm's law apply to AC circuits?
Yes, for purely resistive AC loads using RMS values. Reactive loads (motors, capacitors) involve impedance and power factor instead — see the Watts / Amps / Volts converter.
Why did I get an error?
The calculator needs exactly two positive values. Zero or negative entries can make a pair impossible to solve (for example, dividing by zero).
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