Formula
From power: I = P (W) ÷ V
From resistance (Ohm's law): I = V ÷ R (Ω)
Worked example
A 230 V circuit feeding a 50 Ω heating element: I = 230 ÷ 50 = 4.6 A.
Reference table
From power (DC or PF = 1)
| Power | Amps @ 12 V | Amps @ 120 V | Amps @ 230 V |
|---|---|---|---|
| 60 W | 5 | 0.5 | 0.26 |
| 100 W | 8.33 | 0.83 | 0.43 |
| 500 W | 41.67 | 4.17 | 2.17 |
| 1,000 W | 83.33 | 8.33 | 4.35 |
| 2,000 W | 166.67 | 16.67 | 8.7 |
Where this shows up in the real world
Ohm's-law territory: known voltage, known resistance or wattage, solve for current. It's the resistive-load workhorse — heater elements, dryer coils, lighting strings — and the first calculation in every electronics class from Texas to Toronto. A 240 V dryer element at 12 Ω pulls 20 A; that's the whole sum.
Common mistakes to avoid
It only works as written for resistive loads. The moment a motor, compressor or switch-mode power supply enters the circuit, impedance and power factor take over and the simple V/R answer is wrong — switch to the power-based method with PF. Also confirm whether your '240 V' is actual line voltage; US split-phase nominal can sit anywhere from 228 to 252 V.
Frequently asked questions
Can voltage alone tell me the current?
No — current depends on the load. You need either the power it consumes (I = P/V) or its resistance (I = V/R).
Does Ohm's law work for AC?
For purely resistive AC loads, yes. For motors and electronics, impedance and power factor come into play — use the power-based method with PF instead.
What about three-phase circuits?
Use our kW to amps or kVA to amps calculators, which handle the √3 factor for you.