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Given any 2 of the 4 quantities (Voltage U, Current I, Resistance R, Power P), compute the other 2 instantly.
OHM'S LAW
U = R × I
Variables :
U voltage (V)
R resistance (Ω)
I current (A)
Rationale : the fundamental law linking voltage, resistance and current
in a conductor — discovered by Georg Ohm in 1827. All forms of power
below are derived from it.
ELECTRICAL POWER
P = U × I (voltage × current — direct form)
P = R × I² (resistance × current² — Joule heating)
P = U² / R (voltage² / resistance — fixed-voltage load)
Variables :
P power (W)
Rationale : the three forms are equivalent via U = R × I. The R × I²
form is the most useful one to compute Joule heating (cables, braking
resistors, fuses).
Enter any 2 of the 4 values (voltage, current, resistance, power) and the other 2 are computed automatically. Leave the ones you want computed empty (or set to 0).
This is one of the most basic but most-used calculations in electrical engineering — useful for resistor selection, motor analysis, heater design, and many more.