Electrical calculators

Watts to amps calculator

Amps = watts ÷ volts. On AC, divide by the power factor too, and for three-phase by √3 as well. Enter the power and the voltage to get the current, with the working and a breaker check.

Calculated with electrician.wiki · https://electrician.wiki/calculators/watts-to-amps/

Result

I = 12.5 A

1,500 W at 120 V single-phase draws 12.5 A.

Current: 12.5 A
Real power: 1.5 kW
Apparent power: 1.5 kVA
Formula used: I = P ÷ (V × PF)

12.5 A is 83 % of a 15 A breaker. If the load runs for 3 hours or more (a continuous load), the NEC sizes the branch circuit and its breaker for 125 % of it (210.19(A)(1), 210.20(A)): 15.63 A, which points to a 20 A circuit. Treat this as a starting point; conductor ampacity, terminal ratings and the equipment instructions set the final size.

Show the work

1. Current
$I = \frac{P}{V \cdot PF} = \frac{1,500 W}{120 V \cdot 1} = 12.5 A$
2. Apparent power (what the wiring carries)
$S = \frac{P}{PF} = \frac{1,500 W}{1} = 1,500 VA$

References: NEC 210.19(A)(1), 210.20(A) (2023): 125 % of continuous loads

Voltage and current are RMS values, as a true-RMS meter reads them.
The power entered is real power in watts, and the power factor is the true power factor (watts ÷ volt-amperes).
For a motor, enter the electrical input power. A motor’s kW or hp rating is shaft output; divide it by the efficiency first.

New to this? Power factor explained

Report a problem with this result

How to convert watts to amps

To convert watts to amps, divide the power in watts by the voltage: amps = watts ÷ volts. That is exact for DC and for resistive AC loads such as heaters. For other AC loads divide by the power factor as well, and for three-phase divide by √3 too.

Find the power in watts on the nameplate. For kilowatts, multiply by 1,000.
Find the supply voltage: 120 or 240 V in North America, 230 V in the UK, Europe, India and Australia, 12 or 24 V for vehicles and batteries.
Divide the watts by the volts. For an AC motor or other inductive load, also divide by its power factor.
For a balanced three-phase load, divide by √3 (about 1.732) as well, using the line-to-line voltage.

So 600 watts is 600 ÷ 120 = 5 A on a 120 V circuit and 2.5 A at 240 V. A 1,500 W heater draws 12.5 A at 120 V; a 3,000 W UK kettle draws 13.04 A at 230 V.

How to use the watts to amps calculator

This watts to amps calculator finds the current a load draws from its power rating, for DC, single-phase AC and three-phase AC. Choose the system, enter the power in watts or kilowatts and the supply voltage, and for AC enter the power factor. The answer appears as you type, with the working underneath and a note when the current is close to a common breaker size.

Power is real power: the watts on a heater, lamp or appliance nameplate, or a power meter reading. If the label gives VA or kVA instead, enter that figure and set the power factor to 1: current depends only on the volt-amperes.
Voltage for three-phase can be line-to-line (208, 400, 480 V) or line-to-neutral (120, 230, 277 V). Pick which one you have; the factor in the formula changes with it.
Power factor is 1 for resistive loads and around 0.8 to 0.9 for induction motors at full load. A lower power factor means more current for the same watts.

Watts to amps formulas

Each formula is the power equation solved for current. On AC, dividing by the power factor turns real power back into volt-amperes, which is what sets the current.

I = \frac{P}{V}

Single-phase AC

I = \frac{P}{V \cdot PF}

Three-phase AC, line-to-line or line-to-neutral voltage

I = \frac{P}{\sqrt{3} \cdot V_{LL} \cdot PF} = \frac{P}{3 \cdot V_{LN} \cdot PF}

Apparent power

S = \frac{P}{PF}

Worked examples

A 1,500 W space heater on 120 V

The most common plug-in heater rating in North America, on an ordinary 120 V receptacle circuit.

1. Current
$I = \frac{P}{V \cdot PF} = \frac{1,500 W}{120 V \cdot 1} = 12.5 A$
2. Apparent power (what the wiring carries)
$S = \frac{P}{PF} = \frac{1,500 W}{1} = 1,500 VA$

1,500 W at 120 V single-phase draws 12.5 A.

A 4,500 W water heater on 240 V

A typical residential tank element. Only one element heats at a time in most tanks, so this is the full load.

1. Current
$I = \frac{P}{V \cdot PF} = \frac{4,500 W}{240 V \cdot 1} = 18.75 A$
2. Apparent power (what the wiring carries)
$S = \frac{P}{PF} = \frac{4,500 W}{1} = 4,500 VA$

4,500 W at 240 V single-phase draws 18.75 A.

A 10 kW load on 208 V three-phase

A balanced three-phase heater bank on a 208Y/120 V service.

1. Convert to watts
$P = 10 kW \cdot 1,000 = 10,000 W$
2. Line current (line-to-line voltage)
$I = \frac{P}{\sqrt{3} \cdot V_{LL} \cdot PF} = \frac{10,000 W}{\sqrt{3} \cdot 208 V \cdot 1} = 27.76 A$
3. Apparent power (what the wiring carries)
$S = \frac{P}{PF} = \frac{10,000 W}{1} = 10,000 VA$

10 kW at 208 V three-phase draws 27.76 A per line.

50 kW of motor load on 480 V

Measured input power of a group of motors at a combined power factor of 0.85.

1. Convert to watts
$P = 50 kW \cdot 1,000 = 50,000 W$
2. Line current (line-to-line voltage)
$I = \frac{P}{\sqrt{3} \cdot V_{LL} \cdot PF} = \frac{50,000 W}{\sqrt{3} \cdot 480 V \cdot 0.85} = 70.75 A$
3. Apparent power (what the wiring carries)
$S = \frac{P}{PF} = \frac{50,000 W}{0.85} = 58,824 VA$

50 kW at 480 V three-phase with power factor 0.85 draws 70.75 A per line.

A 3 kW kettle on 230 V

A European or UK kettle at its full rating.

1. Current
$I = \frac{P}{V \cdot PF} = \frac{3,000 W}{230 V \cdot 1} = 13.04 A$
2. Apparent power (what the wiring carries)
$S = \frac{P}{PF} = \frac{3,000 W}{1} = 3,000 VA$

3,000 W at 230 V single-phase draws 13.04 A.

A 15 kW load on 400 V three-phase

A three-phase load on a 230/400 V supply with a power factor of 0.9.

1. Convert to watts
$P = 15 kW \cdot 1,000 = 15,000 W$
2. Line current (line-to-line voltage)
$I = \frac{P}{\sqrt{3} \cdot V_{LL} \cdot PF} = \frac{15,000 W}{\sqrt{3} \cdot 400 V \cdot 0.9} = 24.06 A$
3. Apparent power (what the wiring carries)
$S = \frac{P}{PF} = \frac{15,000 W}{0.9} = 16,667 VA$

15 kW at 400 V three-phase with power factor 0.9 draws 24.06 A per line.

Watts to amps conversion chart

How many amps is a given wattage? Read across for the voltage you have. For a motor or other inductive load, divide the figure by its power factor. The reverse conversion is on the amps to watts calculator.

Current in amps at power factor 1. Three-phase columns use line-to-line voltage and give the current in each line.
Watts	12 V DC	120 V 1-phase	230 V 1-phase	240 V 1-phase	208 V 3-phase	400 V 3-phase	480 V 3-phase
100 W	8.333	0.8333	0.4348	0.4167	0.2776	0.1443	0.1203
250 W	20.83	2.083	1.087	1.042	0.6939	0.3608	0.3007
500 W	41.67	4.167	2.174	2.083	1.388	0.7217	0.6014
600 W	50	5	2.609	2.5	1.665	0.866	0.7217
750 W	62.5	6.25	3.261	3.125	2.082	1.083	0.9021
1,000 W	83.33	8.333	4.348	4.167	2.776	1.443	1.203
1,200 W	100	10	5.217	5	3.331	1.732	1.443
1,500 W	125	12.5	6.522	6.25	4.164	2.165	1.804
1,800 W	150	15	7.826	7.5	4.996	2.598	2.165
2,000 W	166.7	16.67	8.696	8.333	5.551	2.887	2.406
2,400 W	200	20	10.43	10	6.662	3.464	2.887
3,000 W	250	25	13.04	12.5	8.327	4.33	3.608
3,500 W	291.7	29.17	15.22	14.58	9.715	5.052	4.21
5,000 W	416.7	41.67	21.74	20.83	13.88	7.217	6.014
7,500 W	625	62.5	32.61	31.25	20.82	10.83	9.021
10,000 W	833.3	83.33	43.48	41.67	27.76	14.43	12.03

How many amps do appliances use?

These are common appliance ratings converted at the voltages they run on around the world. They are examples: a hair dryer can be anything from about 1,000 to 1,875 W, so read your own appliance’s label and use the calculator. Two traps are worth knowing. A microwave oven’s advertised power is its cooking output; the nameplate input is about half as much again. And a window air conditioner or refrigerator draws several times its running current for a moment when the compressor starts.

Example ratings; your appliance’s nameplate gives its own. Amps at power factor 1: motors and electronics draw somewhat more. The 12 V column is the battery current through a 90 % efficient inverter.
Appliance	Watts	120 V	230 V	240 V	12 V DC
LED bulb	9	0.075 A	0.03913 A	0.0375 A	0.8333 A
Phone charger	20	0.1667 A	0.08696 A	0.08333 A	1.852 A
Laptop charger	65	0.5417 A	0.2826 A	0.2708 A	6.019 A
Ceiling fan	75	0.625 A	0.3261 A	0.3125 A	6.944 A
55-inch LED TV	100	0.8333 A	0.4348 A	0.4167 A	9.259 A
Refrigerator, running	150	1.25 A	0.6522 A	0.625 A	13.89 A
Desktop computer	300	2.5 A	1.304 A	1.25 A	27.78 A
Toaster	900	7.5 A	3.913 A	3.75 A	83.33 A
Coffee maker	1,000	8.333 A	4.348 A	4.167 A	92.59 A
Small window air conditioner	1,000	8.333 A	4.348 A	4.167 A	92.59 A
Microwave oven (1,000 W cooking power)	1,500	12.5 A	6.522 A	6.25 A	138.9 A
Space heater	1,500	12.5 A	6.522 A	6.25 A	138.9 A
Electric kettle, US	1,500	12.5 A	6.522 A	6.25 A	138.9 A
Dishwasher, heating	1,800	15 A	7.826 A	7.5 A	166.7 A
Hair dryer	1,875	15.63 A	8.152 A	7.813 A	173.6 A
Electric kettle, UK and Europe	3,000	25 A	13.04 A	12.5 A	277.8 A
Water heater element	4,500	37.5 A	19.57 A	18.75 A	—
Clothes dryer	5,000	41.67 A	21.74 A	20.83 A	—
Level 2 EV charger, 32 A	7,680	64 A	33.39 A	32 A	—

From amps to a circuit: where this calculation stops

The current is the first number in circuit design, not the last. In the US, a load that runs for three hours or more is a continuous load, and the NEC sizes the branch-circuit conductors and breaker for 125 % of it (210.19(A)(1) and 210.20(A)). The NEC also treats a storage water heater of 120 gallons or less as a continuous load (422.13): the 4,500 W element above draws 18.75 A, so the circuit must be sized for at least 23.44 A. The heater’s installation instructions then give the exact breaker and wire.

The 1,500 W heater is a useful reality check. At 12.5 A it already uses 83 % of a 15 A circuit, and 125 % of it is 15.63 A. Add a 1,200 W hair dryer (10 A) to the same circuit and the breaker will trip.

Motors need more than a conversion: their conductors and short-circuit protection are sized from the NEC full-load current tables, not from watts (430.6(A)(1)); only the overload protection uses the nameplate current. Outside North America the logic is the same in other words: under IEC 60364 and BS 7671 the design current Ib must not exceed the device rating In, which must not exceed the cable’s current-carrying capacity Iz. Either way, take the current from here to the wire size calculator or the cable size calculator, then check the run with the voltage drop calculator.

Watts to amps at 12 V: batteries and inverters

At low DC voltage the currents get large quickly. An inverter also loses some power, so divide the AC load by its efficiency before converting. A 1,000 W AC load through a 90 % efficient inverter draws 92.59 A from a 12 V battery, 46.3 A at 24 V and 23.15 A at 48 V. Each doubling of the battery voltage halves the current and cuts the cable loss to a quarter, which is why larger systems run at 48 V. At these currents voltage drop, not ampacity, usually sets the cable size.

Why measured amps differ from the calculation

The voltage is not nominal. A heater is a fixed resistance (9.6 Ω for 1,500 W at 120 V). At 114 V it draws 11.88 A and makes only 1,354 W. Electronic and motor loads do the opposite: they hold their power, so at 114 V a 1,500 W constant-power load draws 13.16 A.
A 240 V element on 208 V. Apartment buildings with 208Y/120 V service often get 240 V water heaters. The element’s resistance does not change, so a 4,500 W element on 208 V delivers 3,380 W at 16.25 A.
Power factor. 1,500 W at power factor 0.8 is 15.63 A at 120 V, not 12.5 A. The extra current heats the wiring but does no work.
Starting current. Motors draw several times their running current while starting, and cold lamp filaments and transformer magnetizing inrush do the same for a few cycles. Breakers ride through this; a meter’s min/max or inrush mode will capture it.
Meter type. Use a true-RMS clamp on electronic loads; an average-responding meter misreads distorted current.
Generator and UPS ratings. These are usually given in kVA with a power factor of 0.8, so their kW rating is lower. Size them on current or kVA, which the three-phase power calculator gives alongside kW.

Method and verification

The calculator evaluates $I = \frac{P}{k \cdot V \cdot PF}$ , with k = 1 for DC and single-phase, √3 for three-phase with line-to-line voltage and 3 with line-to-neutral voltage. kW is multiplied by 1,000 first. It shares this formula with the amps to watts calculator, so the two always agree. Values are computed in double precision and displayed to four significant figures; nothing is rounded between steps.

The tests check eight cases worked by hand, including 1,500 W at 120 V = 12.5 A and 50 kW at 480 V and power factor 0.85 = 70.75 A. They also confirm that a round trip through amps to watts returns the starting power, that the 80 % note switches on just above 80 % of a breaker size and not at it, that the IEC version of the note quotes no NEC sections, and that zero, negative and out-of-range inputs are refused.

Assumes RMS values, a balanced three-phase load and the true power factor. Updated 2026-10-14. Found a problem? Report it and we log every fix publicly.

Questions people ask

How many amps is 600 watts?

5 A at 120 V, 2.609 A at 230 V and 2.5 A at 240 V, for a resistive load. A 600 W load uses a third of a 15 A, 120 V circuit.

How many amps is 1,000 watts?

8.333 A at 120 V, 4.348 A at 230 V and 4.167 A at 240 V. Through a 90 % efficient inverter, a 1,000 W load draws 92.59 A from a 12 V battery.

How many amps is 1,500 watts?

12.5 A at 120 V, 6.522 A at 230 V and 6.25 A at 240 V, for a resistive load such as a heater. Divide by the power factor for a motor.

How many amps is 2,000 watts?

16.67 A at 120 V, 8.696 A at 230 V and 8.333 A at 240 V. On 120 V that is more than a 15 A circuit can carry, and as a continuous load it needs 125 % of 16.67 A, 20.83 A: more than a 20 A circuit. That is why 2 kW heaters and chargers in North America run on 240 V.

How many amps is 3,000 watts?

25 A at 120 V, 13.04 A at 230 V and 12.5 A at 240 V. That is why 3 kW is the practical ceiling for a UK kettle: at 230 to 240 V it is right at the 13 A that a UK plug fuse allows. In North America, 3,000 W needs a 240 V circuit.

How many amps does a 4,500 watt water heater draw?

18.75 A at 240 V. The NEC treats it as a continuous load, so the circuit is sized for at least 125 % of that, 23.44 A. On a 208 V supply the same element draws 16.25 A and produces only 3,380 W.

How do I convert watts to amps for three-phase?

Divide the watts by √3 (about 1.732), the line-to-line voltage and the power factor. 10 kW at 208 V and power factor 1 is 27.76 A in each line. With a line-to-neutral voltage, divide by 3 instead of √3.

What size breaker do I need for a given wattage?

Convert the watts to amps, multiply by 1.25 if the load runs for three hours or more, and choose the next standard breaker size above that. Then choose a conductor whose ampacity suits the breaker, and follow the equipment’s instructions where they give a maximum breaker size.