kW to Amps Calculator

About the kW to Amps Calculator

A kW to amps calculator converts real power in kilowatts to current in amperes for single-phase and three-phase AC circuits, accounting for the circuit voltage and power factor. This is one of the most practically important electrical calculations in the field: you know how much power a device or system consumes from its nameplate, energy meter, or equipment specification, and you need to determine how much current it actually draws through the circuit so you can properly size the breaker, conductors, and connection hardware. Every major electrical installation code in the world requires knowing the Full Load Current (FLC) to properly protect circuits and conductors. The National Electrical Code (NEC) in the USA, BS 7671 in the UK, AS/NZS 3000 in Australia and New Zealand, and the CEC in Canada all require that overcurrent protection devices and conductors be selected based on the actual current drawn by the load at its rated power. Converting kW to amps is the calculation that bridges the power specification in the equipment manual to the amperage needed to size the installation. The conversion is used in an enormous variety of real-world applications. A homeowner is installing a 7.2 kW Level 2 EV charger: what circuit does it need? A facilities manager is adding a 15 kW HVAC unit to a commercial building: what size breaker and wire? An engineer is sizing a transformer for a 50 kW load bank: what current must the transformer secondary handle? A generator technician is setting the overload protection on a 22 kW genset: at what amperage should the breaker trip? Our free kW to amps calculator handles all the major voltage systems in use worldwide. US residential 120V and 240V single-phase, US commercial and industrial 208V, 240V, and 480V three-phase, European and Australian 230V single-phase and 400/415V three-phase, and UK 230/400V systems are all covered by the same formula with voltage selected from a quick-select list. Power factor presets for resistive loads (1.0), lighting (0.90), motors (0.85), and inductive loads (0.75) make it easy to get an accurate result without needing to know your specific equipment's exact power factor. For motors specifically, the NEC provides a shortcut in Tables 430.248 and 430.250 — listing standard Full Load Current values for motors at specific voltages and horsepower ratings. These table values are required to be used for motor circuit sizing, not nameplate amps alone, because motor nameplate current can vary between individual units of the same specification. The calculator includes reference to these NEC motor table values for the most common motor sizes.

How It Works

The conversion formulas are: for single-phase AC, amps equal (kW times 1,000) divided by (volts times power factor). For three-phase AC, amps equal (kW times 1,000) divided by (volts times power factor times the square root of 3, where the square root of 3 equals approximately 1.732). Worked examples span the full range of applications. Example one — US residential: a 5 kW electric range at 240V, power factor 1.0 (resistive). Amps equal (5 times 1,000) divided by (240 times 1.0) equals 20.83 amps. With the NEC 125% continuous load multiplier: 20.83 times 1.25 equals 26.0 amps, requiring a 30-amp breaker and 10 AWG copper conductors. Example two — commercial HVAC: a 7.5 kW air handler motor at 208V three-phase, power factor 0.85. Amps equal 7,500 divided by (208 times 0.85 times 1.732) equals 7,500 divided by 306.4 equals 24.5 amps. With 125% for continuous: 30.6 amps, requiring a 35-amp breaker. Example three — industrial pump: a 22 kW pump motor at 480V three-phase, power factor 0.88. Amps equal 22,000 divided by (480 times 0.88 times 1.732) equals 22,000 divided by 731.8 equals 30.1 amps. Breaker: 30.1 times 1.25 equals 37.6 amps, use a standard 40-amp breaker.

Tips & Best Practices

• ✓The NEC 125% continuous load rule applies whenever equipment operates for three or more consecutive hours. EV chargers, baseboard heaters, industrial process loads, refrigeration units, and server farms all qualify. Multiply the calculated amperage by 1.25 and then select the next standard breaker size above the result to ensure compliant circuit protection.
• ✓Motor Full Load Current from NEC tables: use NEC Table 430.248 for single-phase motors and Table 430.250 for three-phase motors rather than relying solely on nameplate amperage. The NEC requires these table values as the basis for motor branch circuit component sizing. A 10 HP, 230V single-phase motor has a table FLC of 50 amps regardless of what the nameplate shows.
• ✓EV Level 2 charger circuit sizing: 7.2 kW at 240V equals 30 amps, requiring a 40-amp circuit (30 times 1.25 equals 37.5 amps, round to 40 amps). A 11.5 kW charger draws 47.9 amps, requiring a 60-amp circuit. An 19.2 kW charger draws 80 amps, requiring a 100-amp circuit. All are continuous loads requiring the 125% breaker sizing rule.
• ✓Three-phase motor horsepower conversion: 1 HP equals 0.746 kW. A 20 HP motor equals 14.92 kW. At 460V three-phase with power factor 0.88: amps equal 14,920 divided by (460 times 0.88 times 1.732) equals 21.3 amps. Verify against NEC Table 430.250, which lists 27 amps for a 20 HP, 460V three-phase motor — use the table value for circuit sizing.
• ✓Always use line-to-line voltage in three-phase calculations. The 480V in a 480V three-phase system is the voltage measured between any two of the three hot conductors. Using the line-to-neutral voltage (277V) in the three-phase formula will give a result that is 1.732 times too high — a serious sizing error that would result in dangerous underprotection.
• ✓UK and Australian installations at 230V single-phase and 400V three-phase: the formulas are identical, only the voltage value changes. A 3.5 kW electric cooker in the UK at 230V draws 3,500 divided by (230 times 1.0) equals 15.2 amps, well within a standard 16-amp circuit with 2.5 mm squared cable as specified in BS 7671.
• ✓Power factor estimation when nameplate data is unavailable: resistive loads like electric heaters and incandescent lighting use PF = 1.0. LED and fluorescent lighting with electronic ballasts is typically PF = 0.90 to 0.95. Induction motors at full load range from PF = 0.85 to 0.92. Lightly loaded motors drop to PF = 0.50 to 0.70. Using 0.85 as a conservative default for unknown motor loads is a reasonable starting point.
• ✓Transformer secondary current: a 75 kVA transformer at 208V three-phase has a secondary FLC of 75,000 divided by (208 times 1.732) equals 208 amps. Main breaker sizing: 208 times 1.25 equals 260 amps for continuous load. This is why most 75 kVA transformers are paired with 250-amp or 300-amp main breakers in commercial panelboards.

Who Uses This Calculator

Licensed electricians performing load calculations for service entrance sizing and panel schedules need kW to amps conversions for every load on their schedule. Mechanical and electrical engineers specifying circuit protection and conductor sizes for new construction projects rely on it for every piece of equipment. Homeowners and property managers planning EV charger installations use it to determine the dedicated circuit requirements for their specific charger model. Facilities managers adding new manufacturing equipment verify that existing electrical infrastructure can support the additional load before installation. Generator and transfer switch specifiers translate total facility kW loads into the amperage sizing needed for automatic transfer switch selection. Industrial energy managers use it when correlating energy bills (in kWh) with current measurements from clamp meters to verify system efficiency.