OneCalcApp LogoOneCalcAppConvert. Calculate. Simplify.

Watts to Amps Calculator

ElectricalInstant resultsFormula shown100% in your browser

Convert watts to amps for DC, single-phase AC and three-phase AC supplies. Enter power, voltage and power factor to get current, plus a common-appliance amps table at 120 V and 230 V.

Inputs

120 V or 240 V in North America, 230 V in Europe/India, 400–415 V for three phase

1 for heaters and incandescent lamps, 0.9 for LED drivers, 0.8 for motors

Use 100% when the wattage is input power. Use the motor efficiency when the rating is output (shaft) power.

How to use this calculator: Watts to Amps Calculator

Convert watts to amps for DC, single-phase AC and three-phase AC supplies. Enter power, voltage and power factor to get current, plus a common-appliance amps table at 120 V and 230 V. The example below is calculated by this page's real engine from the displayed inputs.

  1. 1Confirm that the Watts to Amps Calculator matches the quantity or design check you need.
  2. 2Enter Power, Voltage, and Power factor (cos φ) using the units printed beside each field.
  3. 3Select the applicable Supply type options; these choices change the calculation method or factors.
  4. 4Calculate, then follow the substituted equations in the worked example and compare the result with any stated limit.
  5. 5Read the assumptions, warnings and cited references before using the result for a financial, medical or engineering decision.

Input guide and example values

Use values from the same measurement basis and time period. Conditional fields appear only when the related option is selected.

InputExample valueWhy it matters
Supply typeAC single phase (home)Select the option that matches the real installation or scenario.
Power1500 WMeasured or known power used by the calculation engine.
Voltage230 V120 V or 240 V in North America, 230 V in Europe/India, 400–415 V for three phase
Power factor (cos φ)11 for heaters and incandescent lamps, 0.9 for LED drivers, 0.8 for motors
Motor efficiency100 %Use 100% when the wattage is input power. Use the motor efficiency when the rating is output (shaft) power.

Formula, derivation and worked example

Watts measure power; amps measure current. You cannot convert one into the other without knowing the voltage, and for AC supplies also the power factor. This calculator applies the correct formula for DC, single-phase AC and three-phase AC and shows the working, so you can size a breaker, choose a cable or check whether a circuit has spare capacity. The current it gives is the steady running current — motors and compressors draw several times this figure for a second or two at start-up.

DC: I = P / V
AC single phase: I = P / (V × cos φ)
AC three phase: I = P / (√3 × V_LL × cos φ)
If the wattage is output power: I = P / (η × V × cos φ × phase factor)

Substitution steps

  1. 1. Formula
    I = P / (V × cos φ)
    = AC single phase
  2. 2. Substitute
    1,500 ÷ (230 × 1)
    = 6.522 A
  3. 3. Continuous design current
    I × 1.25
    = 8.15 A
  4. 4. Breaker selection
    next standard rating ≥ design current
    = 10 A

Computed example results

Current
6.52 A
AC single phase
Power drawn from supply
1,500 W
same as the entered power
Apparent power
1,500 VA
at pf 1
Design current (continuous, 125%)
8.15 A
NEC 210.19 continuous-load rule
Breaker, non-continuous load
10 A
Breaker, continuous load
10 A
next standard size above the design current
Load per kW
4.35 A per kW
at 230 V

Understanding the result

Read the main result together with supporting checks, assumptions, limits and intermediate values.

For a manual check, repeat the first equation, confirm the units and change one input at a time.

Common mistakes when using Watts to Amps Calculator

  • Do not mix units for Power (W), Voltage (V), Motor efficiency (%). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
  • Do not leave Supply type on the default choice unless that choice matches the real scenario; the selected option can change the calculation path or factor.
  • Do not replace the displayed DC: I = P / V relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
  • Do not treat Current = 6.52 A from the worked example as a universal answer. It belongs to the displayed example inputs and must be recalculated for the actual case.

When the Watts to Amps Calculator is useful

Watts to Amps Calculator is designed for cases where Supply type, Power, Voltage, Power factor (cos φ) are known and you need Current, Power drawn from supply, Apparent power. The page keeps the live calculator, calculation method and worked example together so the result can be checked instead of treated as a black-box number.

Use the calculator for the scope described by its inputs and notes. The displayed method is DC: I = P / V. If the real project or decision needs factors that are not represented here, treat the result as an estimate and add the missing checks separately.

Supply type and Power: what changes the answer

The worked example uses Supply type = AC single phase (home), Power = 1500 W, Voltage = 230 V, Power factor (cos φ) = 1. With those values, Current is 6.52 A. Changing an input should be interpreted according to that field's unit, range, option and hint rather than by the number alone.

For this calculator, the main input roles are: Supply type: Select the option that matches the real installation or scenario. Available choices include DC (battery, solar, 12 V / 24 V / 48 V), AC single phase (home), AC three phase (line-to-line voltage). Power (W): Measured or known power used by the calculation engine. Voltage (V): 120 V or 240 V in North America, 230 V in Europe/India, 400–415 V for three phase Power factor (cos φ): 1 for heaters and incandescent lamps, 0.9 for LED drivers, 0.8 for motors

How to sanity-check a Watts to Amps Calculator result

Start by confirming the entered values and units, then compare the substituted working with the displayed formula or calculation steps. Pay particular attention to Current, because it is the first worked-example output shown by the live engine.

Finally, compare the result with the assumptions, warnings and related calculators on this page. A nearby calculator can be useful as a cross-check when it measures the same workflow from a different input or output direction.

Next logical calculator

Continue with Wire Size Calculator (AWG & mm²)

Wire Size Calculator (AWG & mm²) is directly connected from Watts to Amps Calculator as a source-defined continuation or comparison.

Open Wire Size Calculator (AWG & mm²)

Formula

  • DC: I = P / V
  • AC single phase: I = P / (V × cos φ)
  • AC three phase: I = P / (√3 × V_LL × cos φ)
  • If the wattage is output power: I = P / (η × V × cos φ × phase factor)

Watts measure power; amps measure current. You cannot convert one into the other without knowing the voltage, and for AC supplies also the power factor. This calculator applies the correct formula for DC, single-phase AC and three-phase AC and shows the working, so you can size a breaker, choose a cable or check whether a circuit has spare capacity. The current it gives is the steady running current — motors and compressors draw several times this figure for a second or two at start-up.

Common appliance amps at 120 V and 230 V

Typical running current at power factor 1. Motor loads draw 3–6× these values at start-up.

ApplianceTypical powerAmps at 120 VAmps at 230 V
LED bulb10 W0.08 A0.04 A
Ceiling fan75 W0.63 A0.33 A
Laptop charger90 W0.75 A0.39 A
Television, 55 in LED120 W1.00 A0.52 A
Refrigerator (running)150 W1.25 A0.65 A
Desktop PC300 W2.50 A1.30 A
Washing machine500 W4.17 A2.17 A
Microwave oven1,200 W10.0 A5.22 A
Toaster1,200 W10.0 A5.22 A
Hair dryer1,500 W12.5 A6.52 A
Space heater1,500 W12.5 A6.52 A
Kettle1,800 W15.0 A7.83 A
Window air conditioner1,000 W8.33 A4.35 A
Split AC, 1.5 ton1,600 W13.3 A6.96 A
Electric oven2,400 W20.0 A10.4 A
Clothes dryer3,000 W25.0 A13.0 A
Water heater / geyser4,500 W37.5 A19.6 A
EV charger, level 27,200 W60.0 A31.3 A

Formulas explained

I = P / V

For DC, power is simply volts times amps, so current is power divided by voltage. There is no phase angle and no power factor.

I
Current in amperes (A)
P
Power in watts (W)
V
Voltage in volts (V)

I = P / (V × cos φ)

In AC circuits, voltage and current can be out of step. Watts measure the real power actually used, while the supply has to carry the larger apparent power V × I. Dividing by the power factor recovers the true current the conductor must carry.

cos φ
Power factor, between 0 and 1
V
RMS voltage between line and neutral, e.g. 120 V or 230 V

Resistive loads such as heaters and kettles have a power factor of 1, so watts and volt-amperes are equal.

I = P / (√3 × V_LL × cos φ)

In a balanced three-phase system the total power is delivered over three conductors, and the line-to-line voltage is √3 times the phase voltage. The √3 (1.732) accounts for that, so each line carries less current than a single-phase supply would for the same power.

V_LL
Line-to-line voltage, e.g. 208 V, 400 V or 415 V
√3
1.7320508 — the three-phase constant

Why voltage matters

The same 1,500 W load draws 12.5 A on a 120 V circuit but only 6.5 A on 230 V, and 2.1 A on a 415 V three-phase supply. Higher voltage means lower current for the same power, which is why long runs and large loads use higher voltages.

What power factor does

A power factor below 1 means the supply carries more current than the wattage suggests. A 1,000 W motor at 0.8 pf on 230 V draws 5.4 A, not 4.3 A. Use 1 for heating elements, 0.9 for electronics, 0.8 for induction motors.

Input watts vs output watts

Motor and pump nameplates often state output (shaft) power. The supply has to deliver more than that because of losses. Set the efficiency field to the motor efficiency when your figure is output power; leave it at 100% when it is the input rating.

Sizing the breaker and cable

Circuits with a continuous load are sized at 125% of the running current in the US (NEC 210.19). A 12.5 A continuous load therefore needs a 15.6 A design current, so a 20 A breaker and 12 AWG cable.

Wire Size Calculator

Turn the current from this page into an AWG or mm² conductor size.

Voltage Drop Calculator

Check the 3% branch / 5% total drop limit for the run length.

12V Wire Size Chart

Printable amps × run length chart for 12 V, 24 V and 48 V DC circuits.

Electricity Cost Calculator

Appliance wattage table with monthly running cost at your own tariff.

Power Unit Converter

Convert between watts, kilowatts, megawatts and horsepower.

Worked example

  1. 1A 1,500 W space heater on a 120 V circuit, power factor 1.
  2. 2I = 1500 / (120 × 1) = 12.5 A.
  3. 3As a continuous load it is designed at 12.5 × 1.25 = 15.6 A, so a 20 A breaker with 12 AWG copper.

Assumptions

  • Balanced, sinusoidal supply at the stated RMS voltage.
  • Three-phase results use the line-to-line voltage and give the line current.
  • Running current only — no allowance for motor inrush or harmonics.

Tips

  • For a quick mental check at 120 V, divide watts by 100 for a conservative amps figure; at 230 V divide by 200.
  • Add up the amps of everything on one circuit before deciding it fits — the breaker limit applies to the total.
  • For DC solar and battery circuits, use the actual battery voltage (12.8 V, 25.6 V, 51.2 V) rather than the nominal one for a realistic current.

Warnings

  • Motors, compressors and air conditioners draw 3–6× the running current at start-up; breakers and contactors must tolerate it.
  • Never load a circuit continuously above 80% of the breaker rating.

Standards & references

  • NEC 2023 Article 210 / 310
  • IEC 60364-5-52
  • IS 732

Frequently asked questions

How do I convert watts to amps?

Divide the watts by the volts. For DC, I = P / V. For single-phase AC, divide again by the power factor: I = P / (V × cos φ). For three-phase AC, I = P / (1.732 × V_LL × cos φ).

How many amps is 1,000 watts?

8.33 A at 120 V, 4.35 A at 230 V and 4.17 A at 240 V, assuming a power factor of 1. On a 415 V three-phase supply it is 1.39 A per line.

How many amps is 1,500 watts at 120 V?

12.5 A. That is 83% of a 15 A breaker, so a 1,500 W heater should have its own 15 A circuit, or a 20 A circuit if the load is continuous.

How do I convert amps to watts?

Multiply instead of dividing: watts = amps × volts for DC, amps × volts × power factor for single-phase AC, and amps × volts × 1.732 × power factor for three-phase AC.

Do I use 1.732 for three phase?

Yes, when you are using the line-to-line voltage (208 V, 400 V, 415 V, 480 V). √3 = 1.732 converts between line and phase quantities in a balanced system.

What power factor should I use?

Use 1 for resistive loads such as heaters, kettles and incandescent lamps; 0.9 for LED lighting and switch-mode electronics; 0.8 for induction motors and older air conditioners. If the nameplate states a power factor, use that.

Is the calculated current the same as the breaker size?

No. Pick the next standard breaker above the design current, which for a continuous load is 125% of the running current. A 12.5 A continuous load gives 15.6 A design current, so a 20 A breaker.

What inputs does the Watts to Amps Calculator use?

It uses Supply type, Power, Voltage, Power factor (cos φ), and Motor efficiency. Follow the unit printed for each field and choose any selectable option to match the real scenario.

Related calculators

Keep going with more electrical tools.

Wire Size Calculator (AWG & mm²)

Work out the wire size you need for any AC or DC circuit from load, run length and allowable voltage drop — answer in both AWG and mm², with the governing limit shown.

Voltage Drop Calculator

Free voltage drop calculator with NEC and IEC modes: get percent drop, wire size in AWG or mm², power loss and a 3% branch / 5% total check in seconds.

Cable Sizing Calculator

Size AC power cables to IEC 60364: design current, derating for ambient temperature and grouping, ampacity selection and a voltage-drop cross-check.

DC Cable Size Calculator (12V / 24V / 48V)

Size low-voltage DC cable for 12 V, 24 V and 48 V systems from run length and amps — get the required mm², the matching AWG, voltage drop and a full size chart.

kVA, kW and Amps Calculator

Convert kVA to kW, kW to kVA, kVA to amps or amps to kVA for single-phase and three-phase AC systems using voltage and power factor.

Motor HP to Amps Calculator

Calculate estimated single-phase or three-phase motor full-load current from horsepower, voltage, efficiency and power factor, with starting-current and continuous-duty checks.

Related Engineering Articles

Deeper reading on the engineering behind this calculation.

How to Calculate Voltage Drop in Cables and Circuits

Step-by-step voltage drop calculations for DC, single-phase AC and three-phase AC, with worked examples and acceptable limits.

Read Article →

Full Load Current Calculation – The Foundation of AC Cable Sizing

Learn how to calculate inverter Full Load Current using the three-phase power formula and understand every parameter involved in AC cable sizing.

Read Article →

Short-Circuit Withstand Capability of Power Cables – Thermal Design and Protection Coordination

Understand short-circuit thermal withstand verification, adiabatic cable sizing, fault current, protection clearing time and cable protection coordination.

Read Article →

Applicable Standards and Design Inputs for AC Cable Sizing

Learn the major IEC, NEC and Indian Standards used for AC cable sizing along with the essential electrical, cable and installation inputs required for reliable solar and industrial electrical design.

Read Article →