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This calculator applies the ohms law current relationship. Enter values in the stated units and review the result. Check assumptions and use appropriate professional guidance for safety-critical decisions.Keep exploring
Calculate ohms law current using clearly labelled inputs.
Calculator guide
How the Ohm's law current calculator works
Ohm's law links voltage (V), current (I) and resistance (R). This calculator solves for current:
Current (A) = voltage (V) ÷ resistance (Ω)
Worked examples
A 12 V battery across a 6 Ω resistor: 12 ÷ 6 = 2 A
An LED circuit: 5 V supply minus a 2 V LED leaves 3 V across the resistor. With 150 Ω, I = 3 ÷ 150 = 0.02 A (20 mA), which is right for many small LEDs.
A 230 V heater element of 26.45 Ω: 230 ÷ 26.45 = 8.7 A. The power is 230 × 8.7 = 2,000 W (a 2 kW heater).
The Ohm's law triangle
To find
Formula
Current I
V ÷ R
Voltage V
I × R
Resistance R
V ÷ I
Power P
V × I = I² × R = V² ÷ R
Series and parallel resistors
Series: add them. 100 Ω + 220 Ω = 320 Ω.
Parallel (two resistors): (R1 × R2) ÷ (R1 + R2). 100 Ω and 100 Ω in parallel = 50 Ω.
Practical notes
Check the power rating of resistors. A resistor carrying 20 mA with 3 V across it dissipates 0.06 W, so a common 0.25 W resistor is fine.
Real components aren't perfectly "ohmic". Filament lamps, LEDs and motors change resistance with temperature or operating point.
Circuit breakers and fuses are sized on current, so knowing the current tells you whether a circuit can handle a load.
Safety
Mains voltage (230 V in Australia) can kill. In Australia, it's illegal for unlicensed people to do electrical wiring work. Use this calculator for learning, low-voltage projects and understanding loads, and leave mains work to a licensed electrician.
How do I calculate current from voltage and resistance?
Divide the voltage by the resistance. For example, 9 V ÷ 450 Ω = 0.02 A (20 mA).
How many amps does a 2,400 W appliance draw on 230 V?
About 10.4 A (2,400 ÷ 230), close to the limit of a standard 10 A Australian socket.
What resistor do I need for an LED?
R = (supply voltage − LED voltage) ÷ LED current. For 5 V, a 2 V LED and 20 mA: (5 − 2) ÷ 0.02 = 150 Ω.
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