Ohm’s Law Resistance Calculator
R = V ÷ I • Power and conductance from voltage and current
Voltage may be positive or negative.
Current must be non-zero to calculate resistance.
Quick summary
Enter voltage and current, then click Calculate.
Results
Resistance
— Ω
Power
— W
Conductance
— S
Results are calculated from volts and amps in SI units.
Use this Ohm’s Law Resistance Calculator to calculate electrical resistance from voltage and current. It also calculates power and conductance.
Calculation Method
Resistance = Voltage ÷ Current
R = V ÷ I
Related calculations:
Power = V × I
Conductance = 1 ÷ R
Example
For 12 V and a current of 0.5 A:
R = 12 ÷ 0.5 = 24 Ω
Power = 12 × 0.5 = 6 W
Important Note
Current must be nonzero when calculating resistance with R = V ÷ I. The formula assumes an approximately Ohmic component and does not fully model nonlinear devices or AC impedance.
A calculated resistance or power value does not by itself determine a safe component rating.