Volts to Amps Calculator - Current from Watts or Ohms

Agarapu Ramesh — Editor and content reviewer
Editorially reviewed Reviewed by Agarapu Ramesh, science educator (chemistry). LinkedIn
Last reviewed: May 2026 | Standard electrical engineering formulas

Volts do not convert to amps by themselves. You need the load: either watts or resistance. With watts, I = W / V. With resistance, I = V / R.

Formula at a glance

  • from power: A = W / V
  • from resistance: A = V / R
  • single-phase AC: A = W / (V x PF)

Field note: Asking "how many amps is 240 volts" is incomplete. The load decides the current.

⚡

Calculator Tool

Convert voltage to current

V
W
Result
—

Formulas

With PI = P / V
With RI = V / R

Quick Reference

@120V Amps
100 W 0.83 A
500 W 4.17 A
1000 W 8.33 A
1500 W 12.5 A

Related

Amps to VoltsVolts to WattsOhm's Law

How to use the Volts to Amps Calculator

Use this as a fast electrical check, then compare the result with the nameplate, measured voltage and power factor. The formula is clean. Real panels, motors and UPS loads usually have one extra wrinkle.

Worked example

Example: 1,200 W on 120 V draws 10 A. A 24 ohm load on 120 V draws 5 A.

Practical checks before you trust the number

  • For AC motors and electronics, include PF when using watts.
  • For three-phase current, divide watts by 1.732 x line volts x PF.
  • Resistance changes with heat in some loads.

Common mistake

Asking "how many amps is 240 volts" is incomplete. The load decides the current.

Sources and references

Related calculators

Frequently Asked Questions

From watts: A = W ÷ V (DC) or A = W ÷ (V × PF) for single-phase AC, or A = W ÷ (√3 × V × PF) for three-phase. Example: 2300 W heater on 230 V single-phase, PF 1 → A = 2300 ÷ 230 = 10 A. So a standard 16 A circuit handles it comfortably. We juniors are taught this formula on day one — it gates every cable and breaker selection in residential work.

Ohm's law: I = V ÷ R. Example: 12 V across a 24 Ω heater element gives I = 12 ÷ 24 = 0.5 A. This works perfectly for purely resistive DC loads or AC loads at the instantaneous moment. For AC with inductive or capacitive elements, use impedance Z instead of resistance R. Keep this formula in muscle memory — it's the most-used equation in our profession.

A = W ÷ V → A = 1000 ÷ 120 = 8.33 A for a resistive load (PF = 1). For an inductive load with PF 0.8, A = 1000 ÷ (120 × 0.8) = 10.4 A. So the same wattage draws different current depending on load type. On 230 V Indian supply, the same 1000 W draws only 4.35 A — that's why we use higher voltage for the same power. Less current = thinner cables and lower I²R losses.

Voltage tells you the potential difference, not how much current will flow. Current depends on the load resistance (or impedance) connected across that voltage. From Ohm's law, I = V ÷ R. So 12 V across 12 Ω gives 1 A, but 12 V across 6 Ω gives 2 A. Same voltage, different current. Always remember: voltage is the push, resistance is the obstacle, current is the result. This is one of the first concepts I drill into freshers.

DC: A = V ÷ R using Ohm's law, or A = W ÷ V if power is known. Example: a 24 V battery feeding a 6 Ω heater coil → I = 24 ÷ 6 = 4 A, P = 96 W. Or with a known 96 W load: I = 96 ÷ 24 = 4 A. Both routes give the same answer. For DC there's no PF complication, which makes battery and solar circuit work easier to size.

AC with PF: A = W ÷ (V × PF) for single-phase. Example: a 1500 W motor on 230 V with PF 0.75 → A = 1500 ÷ (230 × 0.75) = 8.7 A. For three-phase, A = W ÷ (√3 × V × PF). Don't forget to use the motor's actual PF, especially at part-load where it can drop to 0.5 or lower. Sizing a breaker on full-load PF can leave you with nuisance tripping.

Yes, and it's one of the most useful sizing tools. Calculate the current of every load on a feeder, sum them, apply diversity (around 0.7 to 0.8 for residential), then pick a breaker at 125% of that for continuous load. Example: 32 A diversified load × 1.25 = 40 A breaker. Cable also sized for 40 A with derating for ambient and bunching. This step-by-step routine prevents trips and protects the wiring.