All workshop tools
Bench calculation
Ohm’s law & power
Enter any two known values. The calculator works out voltage, current, resistance and power—and displays practical units such as mA and kΩ.
Use base units: volts, amps, ohms and watts. For 2.5 mA, enter 0.0025.
Calculated values
Voltage (V)250 V
Current (I)2.5 mA
Resistance (R)100 kΩ
Power (P)625 mW
V = I × R
P = V × I
P = I² × R
P = V² ÷ R
P = V × I
P = I² × R
P = V² ÷ R
Bench safety: Vintage equipment can retain lethal voltage even after it is unplugged. Discharge filter capacitors, use an isolation transformer where appropriate, and stop if you are uncertain.