SpecCalcsReference calculators for the shop floor

Ohm’s Law Calculator

12 V across 2 A gives 6 Ω resistance and 24 W power — enter any two known values below and the calculator solves the other two.

Enter any two — the calculator solves the rest
Voltage12 V
Current2 A
Resistance6 Ω
Power24 W

The formulas — the power wheel

Ohm's law
V=I×RV = I \times R
Power (from V and I)
P=I×VP = I \times V
Power (from I and R)
P=I2×RP = I^{2} \times R
Power (from V and R)
P=V2RP = \frac{V^{2}}{R}
V voltage (volts) · I current (amps) · R resistance (ohms) · P power (watts)

These four quantities are linked by two independent laws: Ohm’s law (V = IR) and the definition of electrical power (P = IV). Substituting one into the other gives twelve rearrangements — the "power wheel" — but they all come from the same two equations. The calculator picks whichever pair of knowns you supply and solves the two unknowns algebraically.

Practical applications

Wire sizing: knowing current and acceptable voltage drop lets you calculate the maximum resistance the wire run can have, which sets the minimum wire gauge. Fuse selection: the expected current at the rated voltage determines the fuse rating. Heat dissipation: P = I²R gives the power lost as heat in a resistor or conductor — critical for PCB thermal design and power-supply efficiency calculations. LED circuits: choosing a current-limiting resistor for an LED is a direct application of V = IR, where V is the supply minus the LED’s forward voltage.