The formula
How it works
Ohm’s law ties together voltage, current and resistance in a circuit: voltage equals current times resistance. Add the power law, P = V·I, and knowing any two values lets you find the rest. Pick what you want to solve for and enter the two you know.
FAQ
Voltage in volts (V), current in amperes (A), resistance in ohms (Ω) and power in watts (W). Keep everything in base units — convert milliamps to amps first, for example.
If resistance is zero the formula divides by zero, which is undefined. Every real circuit has some resistance, so enter a value above zero.
About the Ohm’s law calculator
This calculator solves Ohm’s law and the electrical power equation for any unknown you choose. Ohm’s law is one of the most useful relationships in electronics: it links the voltage across a component, the current flowing through it, and its resistance. Together with the power formula it lets you size resistors, check that a component can handle the load, and understand why a circuit behaves the way it does.
How to use it
Start by choosing what you want to find — voltage, current, resistance or power. The calculator then asks only for the two values it needs. For instance, to find voltage you enter a current of 2 A through a 6 Ω resistor, and it returns 12 V. Switch the target to power and it multiplies voltage by current instead. It also fills in the remaining quantities, so a single calculation gives you the full picture of the circuit. Keep every value in base units.
The formula
The core relationship is Ohm’s law, , which rearranges to and depending on what is unknown. Electrical power adds a second equation, , which can also be written or by substituting Ohm’s law. Because these are simple products and ratios, any two known quantities are enough to solve for the other two.
Where it is used
Electronics hobbyists use it to choose the right resistor for an LED, engineers use it to design and debug circuits, and electricians use the power form to check wiring loads and fuse ratings. The same maths explains battery life, the heat a component gives off, and voltage drop along a long cable. It is one of the first tools anyone learning electronics reaches for, and it stays useful all the way through professional work.