What this converter does
This converter applies Ohm’s law to turn a voltage into the current it drives through a known resistance — or the reverse. Enter the resistance in ohms, type the volts, and read the amps. It updates as you type, so you can size a resistor or check a reading in seconds.
Ohm’s law is the backbone of circuit analysis: current equals voltage divided by resistance. For AC power rather than pure resistance, see the Amps to Watts converter, which also takes voltage and power factor.
The units it covers
Ohm’s law links the three basic circuit quantities — the resistance you enter connects volts and amps.
View all units & their values
| Unit | Symbol | Value | Mainly used |
|---|---|---|---|
| Voltage | V | V | The potential difference driving current |
| Current | A | I | The flow of charge through the circuit |
| Resistance | Ω | R | How much the component opposes current |
| Power | W | P | V × I, if you need the dissipation |
The formula
Current is voltage divided by resistance:
A = V ÷ R (and V = A × R)Where:
- V = the voltage across the component
- R = the resistance in ohms
- A = the resulting current in amps
Worked example
A 12 V supply across a 4 Ω resistor. Find the current.
A = V ÷ R12 ÷ 4 = 3 AThe resistor draws 3 A — and dissipates 12 × 3 = 36 W.
The units in this example
The potential difference across a component, in volts. Divided by resistance it gives the current; multiplied by current it gives power.
- A = V ÷ R
- 12 V ÷ 4 Ω = 3 A
- V = A × R
- P = V × I
The rate of charge flow, in amperes. For a fixed resistance it rises directly with voltage, and it sets how much heat the component dissipates.
- V = A × R
- 3 A × 4 Ω = 12 V
- 1 A = 1 coulomb per second
- R = V ÷ A