QuickCalculators solves any two of voltage, current, resistance and power, returning the remaining pair using V equals I times R and P equals V times I. The Ohm's Law Calculator converts units on each field so milliamps and kilohms combine without manual prefix math.
Solve for voltage, current, resistance or power
Enter any two quantities with units; leave the others blank. The engine recomputes the missing pair and lists formulas used in order. Editing a third value triggers consistency checks against the latest pair edited.
Read Ohm's law
Voltage equals current times resistance in resistive direct-current paths. Ohm's law does not include power by itself; power comes from Joule's relation below. Labels on the form keep V, I and R tied to SI symbols.
Add power with Joule's law
Electrical power P equals V times I in watts when voltage and current are in volts and amps. Alternate forms P equals V squared over R and P equals I squared R appear when division paths avoid zero resistance or zero current.
Use the Ohm's law formula wheel
The wheel lists rearrangements for V, I, R and P given pairs of knowns. sqrt(P times R) finds voltage from power and resistance when current is unknown. The calculator picks algebraically stable paths when denominators could hit zero.
Where Ohm's law stops applying
Nonlinear devices, reactive AC loads, and temperature-dependent resistors violate constant-R models. Semiconductors need curves, not a single ohm value. Treat results as ideal resistive DC estimates unless measurements say otherwise.
Avoid this common mistake
Students quote P equals V times I as part of Ohm's law itself. Ohm's law is V equals I times R; power is Joule's law, paired in practice but not identical. The steps panel names which relation solved each unknown.
Frequently asked questions
What is Ohm's law?
Ohm's law states voltage equals current times resistance in ideal resistive circuits. The Ohm's Law Calculator rearranges that relation with unit conversion on each input.
What is the formula for voltage?
The formula for voltage is V equals I times R when current and resistance are known. Power forms V equals P divided by I or V equals square root of P times R also apply.
How do you calculate power from voltage and current?
To calculate power from voltage and current, multiply V and I in consistent SI units to get watts. The calculator converts prefixes before multiplying.
Is P equals V times I part of Ohm's law?
P equals V times I is Joule's law for power, not Ohm's law, though both appear together on this page when two inputs imply power.
How do you find resistance from power and current?
To find resistance from power and current, use R equals P divided by I squared after converting units. Zero current blocks the division path with an error.
Does Ohm's law work for AC circuits?
Ohm's law works for AC resistive loads with RMS voltage and current at a single frequency, but reactive components need impedance rather than pure R.
Which components do not obey Ohm's law?
Diodes, transistors and arcs do not obey fixed-resistance Ohm's law because their current-voltage curve is nonlinear. Use measured curves instead of one ohm number.
Summary
QuickCalculators resolves voltage, current, resistance and power from any two inputs with V equals I R and P equals V I, plus wheel rearrangements and unit conversion. Power is Joule's law, distinct from Ohm's law proper. Enter two knowns, read the solved pair, and treat outputs as ideal DC resistive estimates.