// physics › Circuits
Find voltage, current or resistance using Ohm's Law V = I R.
V = I R
A mind behind this: Georg Ohm 1789–1854
It links three things in a circuit: voltage (the electrical push), current (how much electricity flows), and resistance (how much the circuit fights the flow). The rule is voltage = current × resistance, or V = I × R.
Think of water in a pipe. Voltage is how hard you push the water, current is how much water flows, and resistance is how narrow the pipe is. Push harder and more flows; use a narrower pipe and less flows. Electricity behaves the same way.
Say a circuit has a current of 2 amperes through a 5-ohm resistor. Voltage = current × resistance = 2 × 5 = 10 volts. So there are 10 volts across that resistor.
Rearrange the same formula. Current = voltage ÷ resistance, and resistance = voltage ÷ current. Pick what you want in the 'Solve for' box and the calculator does the rearranging.
Voltage is measured in volts (V), current in amperes or 'amps' (A), and resistance in ohms (the Ω symbol). One volt pushing across one ohm makes one amp flow.
Everywhere electricity is used — it sets how bright a bulb is, how fast a phone charges, and why thin wires get hot. Engineers use it constantly to choose the right resistor or wire for a job.