Current Calculator (Amps)
Find the current a circuit draws from the supply voltage and the resistance — I = V ÷ R, with the power alongside.
Any two of volts, amps and ohms give the third — and the watts.
How the current calculator (amps) works
Ohm's law in its most-used form: current equals voltage divided by resistance. It answers the question that decides fuse ratings, cable sizes and whether a component survives. Note the shape of it — halving the resistance doubles the current, and a near-zero resistance is a short circuit, which is why the current in a fault is limited only by the wiring.
Formula: V = I R · P = V I
Worked examples
| Inputs | Result | Note |
|---|---|---|
| 12 V across 6 Ω | 2 | 2 A |
| 230 V across 46 Ω | 5 | 5 A — about a 1.15 kW heater |
| 5 V across 220 Ω | 0.0227 | 22.7 mA |
FAQFrequently asked questions
How do I calculate current?
Divide the voltage by the resistance: 12 V across 6 Ω draws 2 A.
What size fuse do I need?
Above the normal running current but below what the cable can carry safely — and always to the equipment's specification, not a guess.
What is a short circuit?
A path with almost no resistance, so the current is limited only by the supply and the wiring — which is why it gets hot so fast.
How many amps does an appliance draw?
Divide its wattage by the supply voltage: a 2,300 W kettle on 230 V draws 10 A.
Is current the same everywhere in a series circuit?
Yes — the same current flows through every component in a series loop. It is voltage that divides.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Measurement Institute — Australia's measurement authority
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.