Electrical•Electrical & Current Sizing•Updated October 22, 2026

Watts to Amps Electrical Calculator

Convert real electrical power in Watts to current in Amperes (Amps) for Direct Current (DC), Single-Phase AC, and balanced Three-Phase systems with power factor adjustment.

Input Parameters

Common Load Presets

Electrical System

Standard single-phase alternating current found in US residential and light commercial outlets.

Real Power *Watts (W)

Enter the total electrical power consumed by the equipment.

Operating Voltage *Volts (V)

RMS voltage for AC or continuous voltage for DC.

Quick Select:

Power Factor (PF) 0.1 to 1.0

Default is 1.0 (pure resistive loads like heaters and incandescent bulbs). When manufacturer equipment documentation specifies a power factor, enter that value.

View Calculated Result & Matched Gear↓

Calculated Electrical Current

10.00 A

Under 120V AC Single-Phase (PF: 1)

125% Continuous Reference

12.5 A

Planning factor for loads running 3+ hrs

Operating Voltage

120 V

AC Single-Phase

Real Load Power

1200 W

1.20 kW

Dedicated Sister Tool

Converting known circuit Amperes and voltage back into total Watts or circuit capacity? Use our dedicated reciprocal calculator:

Open Amps to Watts Electrical Calculator

Conductor & Wire Sizing Notice

Proper wire gauge cannot be determined by amperage alone. Safe conductor sizing depends on one-way run distance, conductor temperature rating (60°C/75°C/90°C), conduit bundling, and acceptable voltage drop (typically 3%).

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Calculation Methodology & Formula

The mathematical relationship between electrical power (Watts), potential difference (Volts), and current flow (Amps) is governed by Ohm's law and Joule's law. In alternating current circuits, current also depends on the phase angle between voltage and current waveforms, characterized by the power factor.

Formula

I = P / ( V × PF )

Variables & Constants

CurrentI (Amperes (A))

The volume of electrical charge flowing through the conductor per second.

Real PowerP (Watts (W))

The rate at which electrical energy is transformed into actual physical work, heat, or light.

VoltageV (Volts (V))

Potential difference driving current through the circuit (DC voltage or AC RMS voltage).

Power FactorPF (Decimal (0.1 to 1.0))

Ratio of real power (W) to apparent power (VA). Pure resistive devices have a PF of 1.0.

Balanced Three-Phase Assumption: Three-phase calculations assume equal current distribution across all three phase conductors.
Power Factor Default: Assumed 1.0 unless equipment nameplate data specifies a reactive power factor.
DC Independence: Direct current has no alternating frequency or inductive reactance, so power factor does not apply.

Verified Worked Calculations

Example Scenario: Converting a 1,500W residential portable space heater operating on a standard 120V household branch circuit.

Identify Circuit Parameters

P = 1,500 Watts, V = 120 Volts AC, PF = 1.0

Electric space heaters use resistive heating elements with unity power factor (PF = 1.0).

Apply Single-Phase AC Formula

I = 1,500 W / (120 V × 1.0) = 12.50 Amperes

Divide real power by the product of voltage and power factor to find operating line current.

Evaluate Continuous-Duty Code Sizing (NEC 210.19 / 210.20)

125% Design Benchmark = 12.50 A × 1.25 = 15.63 A (or 15 A × 0.80 = 12.0 A max continuous)

Under NEC Section 210.19(A)(1) and 210.20(A), branch circuit conductors and standard non-100%-rated breakers serving continuous loads (running 3 hours or more) are sized for at least 125% of continuous load (limiting continuous duty to 80% of breaker rating). On a standard 15A breaker, continuous load benchmark is 12.0A. Because 12.5A exceeds 12.0A, continuous operation requires a 20A branch circuit, whereas intermittent operation under 3 hours is within the 15A breaker rating.

Result: The 1,500W space heater draws 12.50 Amperes of operating current. Under NEC continuous-duty rules for standard breakers, continuous operation requires a 20-Amp branch circuit.

Inverter DC Current Draw: Converting AC Watts to DC Battery Amps

How to size 12V, 24V, or 48V battery wiring and fuses for AC loads powered through an inverter.

When determining how many DC Amps an inverter draws from a battery bank to operate a 120V AC appliance, standard AC formulas (I = P / V) do not account for inversion losses. Power inverters consume energy during conversion (typically operating at 85% to 92% electrical efficiency) and draw ongoing idle tare power.

Inverter DC Current Formula:

I_DC ≈ P_AC ÷ ( V_DC × Inverter Efficiency )

Example: A 1,200W AC microwave powered by a 12V battery bank with a 90% efficient inverter:

I_DC = 1,200 W ÷ ( 12 V × 0.90 ) = 1,200 ÷ 10.8 = 111.1 Amperes DC

12V Battery Bank:

1,200W AC load draws ~111 Amps DC (requires heavy 2 AWG or 1/0 AWG cabling).

24V Battery Bank:

1,200W AC load draws ~55.6 Amps DC (cuts conductor current and I²R heat in half).

48V Battery Bank:

1,200W AC load draws ~27.8 Amps DC (ideal for whole-home solar battery systems).

Note: This is an engineering estimate for battery fuse and cable sizing. Actual draw will vary based on battery state-of-charge (terminal voltage dropping under heavy load) and inverter standby consumption (typically 10W to 30W with zero AC load).

Watts to Amps Quick-Reference Chart

This reference table compares electrical current draw across common residential, DC, and heavy appliance loads. Values are calculated for 12V DC, 120V AC, and 240V AC systems.

Need to convert known current back into total wattage? Use the Amps to Watts Electrical Calculator for reciprocal calculations.

Common Conversion Examples

37 Watts to Amps3.08A @ 12V | 0.31A @ 120V

At 12V DC (such as automotive accessories or small solar panels), 37 Watts draws 3.08 Amps (37W ÷ 12V = 3.08A).

On a standard 120V AC household circuit with unity power factor (PF = 1.0), 37 Watts draws only 0.31 Amps (37W ÷ 120V = 0.31A).

120 Watts Is How Many Amps?1.00A @ 120V | 10.00A @ 12V

On a 120V AC circuit at unity power factor, 120 Watts draws exactly 1.00 Amp (120W ÷ 120V = 1.00A).

On a 12V DC circuit, that same 120 Watts requires 10.00 Amps (120W ÷ 12V = 10.00A), illustrating how lower voltage requires higher current.

1,500 Watts at 120V AC12.50A (15.63A Design Ref)

At 120 Volts with unity power factor (typical for space heaters), 1,500 Watts draws 12.50 Amps of operating current (1,500W ÷ 120V = 12.50A).

For continuous duty (3+ hours), standard 125% sizing benchmarks design current to 15.63 Amps, which requires a 20A branch circuit rather than 15A. Review our complete guide on how many watts a 15-amp or 20-amp circuit can handle.

2,400 Watts to Amps (120V & 240V)10.00A @ 240V | 20.00A @ 120V

At 240 Volts with unity power factor, 2,400 Watts draws exactly 10.00 Amps (2,400W ÷ 240V = 10.00A), with a 125% continuous reference of 12.50 Amps.

At 120 Volts, 2,400 Watts draws 20.00 Amps (25.00 Amps design reference), requiring a dedicated 20A or larger circuit for non-continuous use.

Watts to Amps quick reference table comparing 12V DC, 120V AC, and 240V AC currents with 125% continuous load design references
Power (W)	12V DC Current (A)	120V AC (PF = 1) (A)	240V AC (PF = 1) (A)	120V Continuous Design Ref (125%) (A)	240V Continuous Design Ref (125%) (A)
37 W	3.08 A	0.31 A	0.15 A	0.39 A	0.19 A
60 W	5.00 A	0.50 A	0.25 A	0.63 A	0.31 A
100 W	8.33 A	0.83 A	0.42 A	1.04 A	0.52 A
120 W	10.00 A	1.00 A	0.50 A	1.25 A	0.63 A
300 W	25.00 A	2.50 A	1.25 A	3.13 A	1.56 A
500 W	41.67 A	4.17 A	2.08 A	5.21 A	2.60 A
750 W	62.50 A	6.25 A	3.13 A	7.81 A	3.91 A
1,000 W	83.33 A	8.33 A	4.17 A	10.42 A	5.21 A
1,200 W	100.00 A	10.00 A	5.00 A	12.50 A	6.25 A
1,500 W	125.00 A	12.50 A	6.25 A	15.63 A	7.81 A
1,800 W	150.00 A	15.00 A	7.50 A	18.75 A	9.38 A
2,000 W	166.67 A	16.67 A	8.33 A	20.83 A	10.42 A
2,400 W	200.00 A	20.00 A	10.00 A	25.00 A	12.50 A
3,000 W	250.00 A	25.00 A	12.50 A	31.25 A	15.63 A
3,600 W	300.00 A	30.00 A	15.00 A	37.50 A	18.75 A
5,000 W	416.67 A	41.67 A	20.83 A	52.08 A	26.04 A
7,200 W	600.00 A	60.00 A	30.00 A	75.00 A	37.50 A
10,000 W	833.33 A	83.33 A	41.67 A	104.17 A	52.08 A

Calculation formulas: DC Current: I = P ÷ V. Single-Phase AC Current: I = P ÷ (V × PF), calculated assuming unity power factor (PF = 1.0). Continuous Design Current: I × 1.25.

Power factor assumption: Listed AC current values assume purely resistive loads with a power factor of 1.0. Inductive loads such as air conditioners, refrigerators, and power tools operate with lower power factors (0.75 to 0.90) and draw higher current.

Continuous-load design reference: The 125% continuous-duty columns reflect standard NEC guidelines (Article 100 & 210) where branch circuits serving continuous loads (running 3+ hours) are sized for 125% of the operating current. This is an engineering design reference, not a universal safe-load guarantee.

No fixed conductor sizing from wattage: This table does not specify wire gauges or circuit breaker ratings. Final conductor sizing requires evaluating termination temperature ratings (60°C/75°C/90°C), raceway bundling, ambient temperature derating, voltage drop, and applicable local electrical codes.

Physical & Technical Assumptions

Current conversions depend on phase configuration, power factor, and load duration:

Three-Phase Balance

Default: Balanced (Symmetrical)

Typical Range: 98% to 100% balance

Effect on Current: Unbalanced commercial three-phase loads produce unequal line currents and carry neutral current.

Single-Phase Power Factor

Default: 1.0 (Unity)

Typical Range: 0.75 to 1.0

Effect on Current: Lower power factor increases the current (Amps) required to deliver the same real Wattage.

Continuous Load Factor

Default: 125% (1.25)

Typical Range: 100% or 125%

Effect on Current: Applies to continuous duty loads operating for 3 hours or more per NEC Article 100/210.

Conductor Resistance

Default: Neglected at Terminals

Typical Range: 0 to 5% drop

Effect on Current: Voltage drop over long distances reduces terminal voltage and increases current for constant-power loads.

Parameter	Model Default	Typical Field Range	Effect on Current
Three-Phase Balance	Balanced (Symmetrical)	98% to 100% balance	Unbalanced commercial three-phase loads produce unequal line currents and carry neutral current.
Single-Phase Power Factor	1.0 (Unity)	0.75 to 1.0	Lower power factor increases the current (Amps) required to deliver the same real Wattage.
Continuous Load Factor	125% (1.25)	100% or 125%	Applies to continuous duty loads operating for 3 hours or more per NEC Article 100/210.
Conductor Resistance	Neglected at Terminals	0 to 5% drop	Voltage drop over long distances reduces terminal voltage and increases current for constant-power loads.

Electrical Code & Safety Disclaimer

This calculator provides mathematical current conversions based on user-entered values and does not verify installation safety, breaker compatibility, or conductor ampacity.
Overcurrent protection, circuit breaker sizing, and conductor selection must account for ambient temperature, raceway conductor bundling, termination temperature limits (60°C/75°C/90°C), and local building codes.
The 125% continuous-load reference represents standard NEC overcurrent design guidance for loads operating 3+ continuous hours on non-100%-rated equipment. It does not replace comprehensive conductor sizing or professional electrical engineering approval.
This calculator provides preliminary educational planning estimates and does not certify code compliance, electrical safety, or regulatory approval. Always consult the National Electrical Code (NEC / NFPA 70) and verify critical electrical modifications with a licensed electrician.

Frequently Asked Questions

How do I convert 1,500 Watts to Amps at 120 Volts?

In a standard 120V household circuit with a resistive load (power factor = 1.0), divide 1,500 Watts by 120 Volts: Current = 1,500 / 120 = 12.50 Amps. For continuous operation (loads operating 3 hours or more per NEC Article 100), standard non-100%-rated branch breakers are evaluated at 80% (12.0A on a 15A breaker). Because 12.5A exceeds 12.0A, a 20A branch circuit is required for continuous space heating, whereas non-continuous duty operates within a 15A circuit.

Why does 100 Watts produce different Amps on 12V DC compared to 120V AC?

Current is inversely proportional to voltage (I = P / V). At 120V AC, 100 Watts requires approximately 0.83 Amps. At 12V DC (automotive or solar battery bank), that same 100 Watts draws 8.33 Amps: ten times more current. Higher current creates more resistance and heat, requiring substantially thicker wire.

What is power factor, and when should I change it?

Power factor (PF) is the ratio of real power (Watts) to apparent power (Volt-Amperes) in AC circuits. Pure resistive loads (heaters, incandescent lamps) have a PF of 1.0. Inductive devices with electric motors or compressors (refrigerators, air conditioners, power tools) typically have a PF between 0.75 and 0.90. When equipment nameplate data is available, enter that specific value.

What does the 125% continuous-load reference mean?

Under National Electrical Code (NEC) Article 100, a continuous load is defined as any load where maximum current is expected to continue for 3 hours or more. Under NEC Sections 210.19(A)(1) and 210.20(A), branch circuit conductors and standard non-100%-rated overcurrent devices must be sized for at least 125% of the continuous load (I × 1.25), which restricts continuous duty to 80% of standard breaker rating. This is an installation sizing rule, not a change in mathematical current or an unconditional safety guarantee.

How do you calculate three-phase Watts to Amps?

For a balanced three-phase system using line-to-line voltage (V_LL), divide Watts by the product of the square root of 3 (1.732), the line-to-line voltage, and the power factor: I = P / (√3 × V_LL × PF). For example, a 10,000W load at 480V with PF 0.85 draws approximately 14.15 Amps per line.

How do you calculate inverter DC amp draw from AC watts?

To calculate how many DC Amps an inverter draws from a battery bank, divide the AC load wattage by the product of battery DC voltage and inverter efficiency: I_DC = P_AC / (V_DC × Efficiency). For example, running a 1,200-Watt appliance through a 12V inverter with 90% efficiency draws approximately 111.1 Amps DC (1,200 / [12 × 0.90]). On a 24V battery bank, that same 1,200W load draws only 55.6 Amps DC, and on a 48V bank it draws 27.8 Amps DC. Always include a safety margin for inverter standby idle draw and peak compressor motor surge.

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Circuit Conductor Sizing & Continuous Load Rules

Watts to Amps Circuit Sizing: Breaker Ratings & Conductor Ampacity Tables

Calculating the current draw of any electrical load ensures circuit breakers, extension cords, and copper conductors operate safely without thermal overload or nuisance trips.

The Watts to Amps Calculation Formula

Amperes measure the rate of electrical charge flow. To determine current from known power in watts, divide total wattage by the operating line voltage and load power factor:

Amps = Watts ÷ (Volts × Power Factor)

Direct Current (DC): Amps = Watts ÷ Volts | Single-Phase AC (Unity PF): Amps = Watts ÷ Volts

Watts to Amps Conversion Table (12V DC, 120V AC & 240V AC)

Comprehensive conversion chart across common residential wattages, specifying current draw, recommended NEC 125% breaker sizing, and minimum copper conductor gauge:

Power (Watts)	12V DC	120V AC	240V AC	NEC Breaker	Copper Wire	Common Applications
37 Watts	3.08 A	0.31 A	0.15 A	15A	14 AWG	Desk fan, modem, LED aquarium light
60 Watts	5.00 A	0.50 A	0.25 A	15A	14 AWG	Standing lamp, compact soldering iron
100 Watts	8.33 A	0.83 A	0.42 A	15A	14 AWG	Laptop power adapter, small soundbar
120 Watts	10.00 A	1.00 A	0.50 A	15A	14 AWG	Slow cooker low setting, TV display
300 Watts	25.00 A	2.50 A	1.25 A	15A	14 AWG	Desktop workstation, refrigerator running
500 Watts	41.67 A	4.17 A	2.08 A	15A	14 AWG	Gaming PC under load, 1/3 HP sump pump
750 Watts	62.50 A	6.25 A	3.13 A	15A	14 AWG	1 HP motor, standard kitchen blender
1,000 Watts	83.33 A	8.33 A	4.17 A	15A	14 AWG	Small microwave, steam iron, toaster
1,200 Watts	100.0 A	10.00 A	5.00 A	15A	14 AWG	Hair dryer medium setting, waffle maker
1,500 Watts	125.0 A	12.50 A	6.25 A	20A (Cont.)	12 AWG	Ceramic space heater, electric kettle
1,800 Watts	150.0 A	15.00 A	7.50 A	20A (15A Max)	12 AWG	Commercial hair dryer, 15A branch peak
2,000 Watts	166.7 A	16.67 A	8.33 A	25A / 15A	10 / 14 AWG	Large pressure cooker, table saw
2,400 Watts	200.0 A	20.00 A	10.00 A	30A / 15A	10 / 14 AWG	Commercial microwave, 20A branch peak
3,000 Watts	250.0 A	25.00 A	12.50 A	35A / 20A	8 / 12 AWG	RV 30A service peak, water heater
3,600 Watts	300.0 A	30.00 A	15.00 A	40A / 20A	8 / 12 AWG	RV 30A full load, electric clothes dryer
5,000 Watts	416.7 A	41.67 A	20.83 A	30A (240V)	10 AWG	Central AC compressor, water heater
7,200 Watts	600.0 A	60.00 A	30.00 A	40A (240V)	8 AWG	Electric vehicle Level 2 charging (30A)
10,000 Watts	833.3 A	83.33 A	41.67 A	60A (240V)	6 AWG	Whole-home standby generator backup, oven

Worked Technical Calculations & Circuit Sizing Rules

37 Watts to Amps: Household Devices & DC Electronics

A 37-watt load represents typical low-power equipment like standing desk fans, LED fixtures, and networking hubs.

On standard 120-volt AC power, 37 watts draws just 0.31 amps (37 ÷ 120). This places minimal load on a 15-amp branch circuit.

When operating on a 12-volt battery system, that same 37-watt draw requires 3.08 amps (37 ÷ 12), demanding properly sized DC wiring to avoid voltage sag.

The NEC 125% Rule for Circuit Breaker Sizing

Under National Electrical Code Article 210.20, branch circuit overcurrent protective devices must be rated for at least 125% of continuous loads plus 100% of non-continuous loads.

A continuous load is defined as any electrical load operating continuously for 3 hours or longer, such as space heaters, water heaters, and electric vehicle supply equipment.

For example, a continuous 1,500-watt, 120-volt portable heater draws 12.5 amps. Sizing the breaker requires 12.5A × 1.25 = 15.625 amps, mandating a 20-amp branch circuit breaker.

American Wire Gauge (AWG) Sizing Standards

Copper conductor sizing must match the circuit breaker rating to prevent overheating inside walls and electrical enclosures.

NEC Table 310.16 specifies standard non-metallic sheathed cable limits: 14 AWG copper for 15-amp circuits, 12 AWG for 20-amp circuits, and 10 AWG for 30-amp circuits.

For circuits exceeding 50 feet in length, consider up-sizing one wire gauge size to counteract resistive voltage drop and maintain clean terminal voltage.