Ohm's Law Calculator
Inputs
R = V / I — calculated from the values you entered. Clear one of those to edit this instead.
P = V × I — calculated from the values you entered. Clear one of those to edit this instead.
Tab to move between fields
The circuit, live
12 volts pushes 2 amps through 6 ohms, dissipating 24 watts — the bulb is glowing brightly.
Results
Voltage (V)
12
Calculate resistance
R = V / I
= V = 12 V, I = 2 A
= 6 Ω
Derived from the two values you entered using R = V / I.
Calculate power
P = V × I
= V = 12 V, I = 2 A
= 24 W
Derived from the two values you entered using P = V × I.
The V-I-R-P wheel
Using V and I — the highlighted formulas are the ones being applied.
- V = I × R
- V = P / I
- V = √(P × R)
you entered
- I = V / R
- I = P / V
- I = √(P / R)
you entered
- R = V / I←
- R = V² / P
- R = P / I²
calculated
- P = V × I←
- P = V² / R
- P = I² × R
calculated
Ohm's law
- 1.Divide volts by amps
This is the definition of resistance rather than a consequence of it: an ohm IS one volt per amp. Dividing the two you measured gives the resistance that must be present.
- 2.Multiply volts by amps for power
A volt is a joule per coulomb and an amp is a coulomb per second, so their product is joules per second — watts. The charge unit cancels, which is why the multiplication is dimensionally allowed at all.
Where the units go
- volts ÷ amps A→Ω
- volts × amps C→W
Georg Ohm published the proportionality between current and voltage after measuring it on wires of varying length, using a thermocouple for a steady source. The work was poorly received at first — his own ministry considered it insufficiently rigorous.