Power → current
Watt to Amp
Calculator
Watts alone don't tell you the amps — you need the voltage. A = W ÷ V, so the same power draws fewer amps at higher voltage. Convert watts to amps (or back) for DC, single- and three-phase — then size the wire and breaker in a tap.
A watt-to-amp calculator built for pros — clear enough for anyone.
1500 W is the same power at every voltage — but the current halves each time you double the volts. That's why 240 V appliances draw fewer amps than 120 V ones.
Every circuit type
DC · single- & three-phase
Both directions
Watts ↔ amps, one tool
Free & private
No signup, runs in your browser
Artie has taught physics and electrical theory for over a decade and consulted on real-world electrical design — so every tool here is grounded in both the theory and the field.
University physics lecturer·Consulted on commercial electrical systems·Last reviewed Jul 2026
Watt to Amp Calculator
Convert watts ↔ amps for DC and AC single- or three-phase.
A starting point — final size depends on continuous load, derating & terminal ratings.
Enter values to convert.
Conversion result
Next: size the circuit
A starting point — the final size still depends on continuous-load 125%, conductor derating and terminal ratings.
Same power, different voltage — tap to use
Method — the formula for this conversion
Power factor (PF) applies to AC only; resistive loads use PF = 1. Apparent power VA = real power ÷ PF. Three-phase L-L uses √3 (1.732); L-N uses 3. Horsepower = W ÷ 746. This converts power ↔ current only — it does not size a breaker or wire.
How to use it
How to use the watt-to-amp calculator
It takes three inputs — the current type, the power in watts, and the voltage. Add a power factor for AC, and it converts watts to amps instantly. From there, one tap routes you to sizing the wire and breaker for that current.
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01
Pick your current type
Choose DC, AC single-phase, or AC three-phase — it sets the formula the tool uses.
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02
Enter watts & volts
Type the power (watts or kW) and the voltage. You always need both — watts alone can't give you amps.
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03
Set the power factor
For AC, add the power factor — 1.0 for resistive loads, about 0.8 for motors. DC skips this step.
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04
Read the amps & size it
Get the current instantly — then size the wire, breaker, or check voltage drop for that amperage in a tap.
The core idea
What determines the amps
One division does the work — voltage is the divisor.
Amps come from one relationship: current = power ÷ voltage. Watts set the power, volts set the pressure, and the amps fall out of dividing one by the other. For AC, the power factor — and, for three-phase, √3 — adjust the result.
The power triangle — cover what you want to find
Voltage is the divisor. Double the volts, halve the amps — that's why 240 V draws half the current of 120 V for the same power.
For AC, two adjusters. Divide also by the power factor (1.0 for resistive loads, ~0.8 for motors). For three-phase, divide by √3 as well — the same power spread across three conductors draws less per phase.
Amps = Watts ÷ Volts — ÷ PF for AC · ÷ √3 for three-phase
The method
The watts-to-amps formula
Every case starts from the same base — amps = watts ÷ volts. AC adds the power factor as a divisor, and three-phase adds √3 (line-to-line) or 3 (line-to-neutral). Pick the current type and the tool applies the right one.
I = W ÷ V
Batteries · solar · DC equipment
I = W ÷ (V × PF)
Home outlets · most appliances
I = W ÷ (√3 × V × PF)
Industrial · line-to-line voltage
I = W ÷ (3 × V × PF)
Three-phase · line-to-neutral voltage
Amps → watts: W = V × I · × PF for AC · × √3 for three-phase
Worked example
How many amps is 1500 watts?
It depends on the voltage. A 1500 W resistive load draws 12.5 A at 120 V — but only 6.25 A at 240 V, because doubling the voltage halves the current. A motor's power factor pushes it the other way.
120 V 1500 ÷ 120 = 12.5 A
240 V 1500 ÷ 240 = 6.25 A
motor 1500 ÷ (120 × 0.8) = 15.6 A
At 120 V, 1500 W draws 12.5 A — comfortable on a 15 A circuit (size for 20 A if it runs 3+ hours). Raise the voltage and the current drops; a motor's lower power factor raises it.
The reference
Voltages, power factor & watts vs VA
A few things sharpen the conversion: the voltage your circuit runs at, the power factor for AC loads, and the difference between watts (real power) and VA (apparent power). Here's the reference.
| Voltage | Type | Typical use |
|---|---|---|
| 12 V | DC | Battery, RV, solar |
| 24 V | DC | Solar, control circuits |
| 48 V | DC | Solar, telecom, EV |
| 120 V | AC · 1-phase | Home outlets, lighting |
| 240 V | AC · 1-phase | Dryer, range, EV, AC |
| 208 V | AC · 3-phase | Commercial (line-to-line) |
| 277 V | AC · 1-phase | Commercial lighting (L-N) |
| 480 V | AC · 3-phase | Industrial (line-to-line) |
Pick the voltage your circuit actually runs at — the same watts draw very different amps at 12 V vs 240 V.
Typical values
Resistive (heaters, incandescent) 1.0 · induction motors 0.8–0.85 · LED & electronics ~0.9. Leave PF at 1.0 for resistive loads.
Continuous loads
Running 3+ hours? The circuit is sized at 125% of the amps (NEC 210.20). 12.5 A → size for 15.6 A. Size the breaker →
Kilowatts
kW is just watts × 1000 — a 4.5 kW heater is 4500 W. The tool's kW input converts it for you.
√3 or 3
Line-to-line divides by √3 (≈1.732); line-to-neutral divides by 3. Match it to how your voltage is measured.
Correction
A low power factor draws more amps for the same real power — and can mean utility penalties. Check power factor →
What affects it
What changes the amps — and the common mistakes
For the same watts, the amps move with three things — the voltage (the big lever), the power factor on AC, and the phase. The common mistakes go wrong on exactly these: forgetting power factor, confusing watts with VA, or using the wrong voltage.
What changes the amps
the three levers
- VoltageThe biggest lever — amps move inversely. Double the voltage and the current halves.
- Power factorAC only. A lower power factor (motors ~0.8) draws more amps for the same real power.
- PhaseThree-phase divides by √3, so the same power draws less current per conductor.
- The wattageMore watts means more amps, directly — doubling the load doubles the current.
Common conversion mistakes
what trips people up
- 01Don't forget power factorUsing PF 1.0 for a motor undersizes the amps — motors run around 0.8.
- 02Don't confuse watts with VAVA and kVA are apparent power — a different formula, with no power factor.
- 03Don't use the wrong voltageA 120 V figure is double the amps of the same load at 240 V.
- 04Don't mix up the phaseSingle vs three-phase, and L-L vs L-N, change the divisor (√3 or 3).
The big lever
Double the voltage, halve the amps
The same power at 240 V draws half the current it does at 120 V — which is exactly why big appliances run on 240 V and heavy equipment on 480 V. Higher voltage, thinner wire.
Don't forget power factor for motors. A motor rated 1500 W at PF 0.8 draws 15.6 A, not the 12.5 A you'd get assuming a perfect power factor — a 25% difference that would undersize the wire and breaker.
Quick chart
How many amps — by watts & voltage
Pick a wattage and a voltage to get the amps (or flip it to go amps → watts). For the most-asked one — how many amps is 1500 watts — it's 12.5 A at 120 V, or 6.25 A at 240 V.
Resistive load (power factor 1.0). For motors, three-phase, or a power factor, use the calculator at the top.
Current
12.5 A
1500 W ÷ 120 V
Common watts → amps
| Watts | 120 V | 240 V | 12 V solar / battery |
|---|---|---|---|
| 500 W | 4.17 A | 2.08 A | 41.7 A |
| 1000 W | 8.33 A | 4.17 A | 83.3 A |
| 1500 W | 12.5 A | 6.25 A | 125 A |
| 2000 W | 16.7 A | 8.33 A | 167 A |
| 3000 W | 25.0 A | 12.5 A | 250 A |
The same power draws ~10× the current at 12 V that it does at 120 V — why battery and solar wiring is so heavy.
| Watts | 120 V | 208 V | 240 V | 277 V | 480 V |
|---|---|---|---|---|---|
| 1000 W | 8.33 A | 4.81 A | 4.17 A | 3.61 A | 2.08 A |
| 1500 W | 12.5 A | 7.21 A | 6.25 A | 5.42 A | 3.13 A |
| 2000 W | 16.67 A | 9.62 A | 8.33 A | 7.22 A | 4.17 A |
| 3000 W | 25 A | 14.42 A | 12.5 A | 10.83 A | 6.25 A |
| 5000 W | 41.67 A | 24.04 A | 20.83 A | 18.05 A | 10.42 A |
How many amps is 1500 watts?
It depends on the voltage. A 1500 W resistive load draws 12.5 A at 120 V, or 6.25 A at 240 V — watts alone can't give you amps, because amps = watts ÷ volts.
Do I need the voltage to convert watts to amps?
Yes, always. Watts measure power and amps measure current — you can only get from one to the other through the voltage. The same 1500 W is 12.5 A at 120 V but 125 A at 12 V.
What's the difference between watts and amps?
Watts are power — the rate of energy use. Amps are current — the flow of electricity. Volts tie them together: watts = volts × amps. A device's wattage is fixed, but its amps depend on the voltage it runs at.
What is power factor, and do I need it?
Power factor is the ratio of real power (watts) to apparent power (VA) on an AC circuit, from 0 to 1. Resistive loads are 1.0; motors run around 0.8. Leave it at 1.0 for DC or resistive loads; for motors, use the real value or the amps come out too low.
How do I convert kW to amps?
Convert kW to watts first — multiply by 1000 — then divide by the voltage. A 4.5 kW (4500 W) heater at 240 V draws 18.75 A. The tool's kW input does that step for you.
What's the difference between watts and VA (or kVA)?
Watts are real power; VA and kVA are apparent power. They're equal only at power factor 1.0. Nameplates on UPS units, transformers, and generators often read VA/kVA — convert those with the Ampere calculator, which handles apparent power directly.
What's the three-phase formula?
For three-phase line-to-line: amps = watts ÷ (√3 × volts × power factor), where √3 ≈ 1.732. If your voltage is measured line-to-neutral, divide by 3 instead of √3.
Why does 240 V draw fewer amps than 120 V?
Because amps and voltage are inversely related for the same power: double the voltage and the current halves. That's why 240 V appliances and 480 V equipment draw less current — and can use thinner wire — than the same load at 120 V.
Keep going
Related electrical calculators
Converting to amps is the first step. These pick up from there — size the wire for that current, protect it with the right breaker, and check the run — all on the same NEC-based engine.
How we keep this accurate
Watt-to-amp conversion uses amps = watts ÷ (volts × power factor), with √3 for three-phase — the standard electrical relationships. Sizing tools follow the National Electrical Code (NEC 2023). Results are for planning and estimating. Code adoption, local amendments, and field conditions vary — verify with your AHJ and a licensed electrician before installation.