kW to Amps Calculator
Current in amps from power in kilowatts and voltage in volts
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What this calculator computes
Kilowatts to amps conversion is the same inverse-power calculation as watts to amps, scaled up by a factor of 1000 to handle the larger loads where kilowatt ratings are conventional. The formula is I = (kW × 1000) / (V × PF) for DC and AC single-phase, and I = (kW × 1000) / (√3 × V_LL × PF) for balanced three-phase systems. Most appliance and equipment ratings cross over from watts to kilowatts somewhere between 1 kW and 5 kW: small appliances are labelled in watts, large appliances and motors are labelled in kilowatts, and industrial equipment is almost always in kW or hp. The calculation matters most at the kilowatt scale because that is where conductor sizing, breaker selection, transformer sizing, and utility-service capacity all become significant cost drivers. A 7.4 kW level-2 EV charger on a 240 V US circuit pulls 30.8 A and requires a 40 A breaker on 8 AWG conductor; the same 7.4 kW charger on a 230 V European circuit pulls 32.2 A and is at the upper limit of a domestic 32 A connection. This calculator supports DC, AC single-phase, and AC three-phase modes with adjustable power factor, returning the steady-state RMS current that determines NEC ampacity selection. For three-phase motors specified by hp rather than kW, multiply hp by 0.746 to get input kW, then apply the formula here using the rated motor PF (typically 0.85–0.9 for premium-efficiency three-phase motors).
Calculator
The formula
Formula
I (A) = (kW × 1000) / (V × PF) (3-phase: I = (kW × 1000) / (√3 × V × PF))
Worked example
When to use this calculator
Use this calculator for the larger residential, commercial, and industrial loads where wattage is conventionally given in kW: EV chargers, heat pumps, electric tankless water heaters, induction cooktops, three-phase motors, commercial HVAC compressors, and utility-service feeders. The most common scenario is sizing the conductor and breaker for a new dedicated circuit — particularly the EV-charger and heat-pump circuits driving most residential service upgrades in 2025–2030 — where the kW rating from the nameplate must be translated into the breaker amperage that determines wire gauge, conduit fill, and panel slot consumption. The calculator is also useful for verifying that an existing 100 A or 200 A service can absorb a planned high-kW addition without exceeding the NEC 80% continuous-load limit. For three-phase commercial work, use the line-to-line voltage and a realistic motor PF (0.85 is a common assumption for unspecified motor loads) rather than 1.0, which under-states the actual current draw on inductive equipment.
Common input mistakes
- Forgetting the 1000 multiplier when converting from kW to W. A 7.4 kW charger at 240 V is 30.8 A, not 0.0308 A; entering kW as if it were watts produces a current 1000× too low. The calculator handles the unit conversion internally, but spreadsheet hand-checks that mix kW and W in the same formula will produce nonsense.
- Using nominal supply voltage instead of derated voltage at the panel. Long service drops, undersized utility transformers, and aged conductors can sag the panel voltage 5–10% below nominal under load. Sizing a 7.4 kW charger circuit at the nominal 240 V assumption when the panel actually delivers 228 V under load means the steady-state current is 32.5 A rather than 30.8 A — close to the 32 A continuous limit on a 40 A breaker.
Frequently asked questions
How do I convert kW to amps?
Multiply the kilowatt figure by 1000 to convert to watts, then divide by the supply voltage and power factor: I = (kW × 1000) / (V × PF). For three-phase circuits, also divide by √3 using the line-to-line voltage. The result is the steady-state RMS current in amps, which is the figure NEC tables use for conductor and breaker sizing.
How many amps is a 7.4 kW EV charger?
A 7.4 kW Level 2 EV charger draws 30.8 A on a 240 V US split-phase circuit and 32.2 A on a 230 V European single-phase circuit, both at unity power factor. NEC 625.41 requires the circuit to be sized at 125% of continuous current, so the 30.8 A US installation requires a 40 A breaker on 8 AWG copper conductor. The European 32.2 A installation is right at the typical 32 A domestic feed limit and may require service upgrade.
What is the difference between kW and kVA for sizing?
Kilowatts (kW) is real power and kilovolt-amperes (kVA) is apparent power; the two are equal only when power factor equals 1. Generators, UPS systems, and transformers are rated in kVA because their windings must carry the full apparent current regardless of PF. A 10 kVA generator can deliver 10 kW only at unity PF; on a 0.8 PF load the real-power output drops to 8 kW even though the windings are still at full capacity.
How do I size a three-phase motor circuit from kW?
For a three-phase motor, use I = (kW × 1000) / (√3 × V_LL × PF × η), where η is the motor efficiency. NEC 430.6 actually requires sizing from the FLC (full-load current) tables rather than from nameplate data for short-circuit and overload protection, with the breaker sized at 250% of FLC for instantaneous-trip types. The calculator here gives a useful sanity check on the FLC-table value but should not replace the table lookup for code-compliant installation.
Does this calculator handle 480 V three-phase?
Yes — switch the current type to AC three-phase and enter 480 in the voltage field. The calculator applies the √3 factor automatically: a 50 kW load on 480 V three-phase at PF 0.85 draws 50000 / (1.732 × 480 × 0.85) = 70.7 A. The 480 V three-phase delta system is the most common US commercial-industrial supply for motors and HVAC compressors, with 277 V derived as the line-to-neutral voltage for lighting circuits.