Amps to kW Calculator
Power in kilowatts from current in amps and voltage in volts
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What this calculator computes
Amps to kilowatts conversion turns a measured or rated current into a real-power figure in kilowatts, the conventional unit for commercial and industrial loads. The math is the same as amps to watts (P = V × I × PF for single-phase, P = √3 × V_LL × I × PF for three-phase) divided by 1000 to scale into kilowatts. This conversion is most useful at the panel, switchgear, and utility-service scale, where amperage is what gets read off clamp meters and breaker labels but kilowatts is what gets billed and what drives transformer and generator sizing. A 200 A US residential service at 240 V split-phase can deliver up to 48 kW on paper but is typically sized for 32–40 kW peak load after diversity and continuous-duty derating; a 400 A commercial service at 480 V three-phase delivers up to 332 kW and is the typical service for a small industrial unit or restaurant. This calculator supports DC, AC single-phase, and AC three-phase modes with adjustable power factor, returning the real power in kilowatts and the apparent power in kilovolt-amperes. The kVA result is what generator and transformer nameplates list, and the difference between kVA and kW immediately reveals how reactive the load is: a 50 kVA / 50 kW load is purely resistive, while a 50 kVA / 35 kW load has PF = 0.7 and significant inductive reactance.
Calculator
The formula
Formula
kW = (V × I × PF) / 1000 (3-phase: kW = (√3 × V × I × PF) / 1000)
Worked example
When to use this calculator
Use this calculator when you need to translate amperage readings into kilowatt loadings — typically during energy auditing, generator sizing, transformer selection, peak-demand analysis, and utility-billing back-checks. The most common scenario is reading current on the main service lugs with a clamp meter and translating to real-power demand to compare against utility bills, peak-demand charges, or generator capacity. The calculator is also useful for verifying that a planned load addition will not push a transformer past its kVA rating, where the kVA at the rated current depends on the line-to-line voltage of the secondary. For three-phase systems, the line-to-line voltage and √3 factor are essential — using single-phase mode on a three-phase reading under-states the kW by 42%. The PF input matters most for motor-heavy and HVAC-heavy loads; for primarily resistive lighting and electric-heat loads, PF ≈ 1 makes the kW and kVA results nearly identical.
Common input mistakes
- Reading line current on one phase of a three-phase circuit and treating it as the total load current. Three-phase calculations already account for all three phases through the √3 factor when given the line current of any one phase (assumed balanced). Multiplying the per-phase current by 3 before applying the formula triple-counts the load and produces a result roughly 1.73× too high.
- Using neutral-wire current as the load current. The neutral conductor in a single-phase or three-phase wye system carries only the imbalance between the hot conductors, not the load current. Clamp meters must be placed around the hot conductor (or all hots simultaneously for three-phase) to get the correct figure for power calculation.
Frequently asked questions
How do I convert amps to kW?
Multiply current (amps) by voltage (volts) and power factor, then divide by 1000 to scale watts into kilowatts: kW = (V × I × PF) / 1000. For three-phase circuits, also multiply by √3 (≈ 1.732) using the line-to-line voltage. The result is real power in kW; apparent power in kVA is the same calculation without the PF term.
How many kW does a 200 A service deliver?
A 200 A US residential service at 240 V split-phase delivers up to 48 kW (200 × 240 / 1000) of capacity at unity power factor, but NEC 80% continuous derating reduces the practical sustained capacity to 38.4 kW. A 200 A UK domestic service at 230 V single-phase delivers 46 kW, and a 200 A commercial 480 V three-phase service delivers 166 kW. Average residential peak demand is typically 5–10 kW, so 200 A leaves substantial headroom for EV chargers and heat pumps.
What is the relationship between kW and kVA?
Kilowatts is real power (energy actually consumed) and kilovolt-amperes is apparent power (the product of RMS voltage and current). The two are linked by the power factor: kW = kVA × PF. For purely resistive loads (PF = 1) the values are equal; for typical mixed commercial loads (PF 0.85) the kW is 85% of the kVA. Generators and transformers are rated in kVA because the windings must carry the full apparent current regardless of PF.
Does the calculator handle DC?
Yes — select DC as the current type and the formula reduces to kW = (V × I) / 1000, with no power factor or √3 factor applied. DC mode is the right choice for solar PV string output, battery-bank discharge analysis, and DC motor sizing. The PF input is ignored in DC mode (effectively held at 1) because DC has no reactive power.
Why is my measured kW lower than the appliance nameplate?
Appliance nameplates list maximum or peak power, while measured power is the time-averaged real power during operation. A 1500 W microwave only draws 1500 W during the magnetron-on portion of its duty cycle, which on lower power settings can be a small fraction of the time. Tankless water heaters draw their full kW only when delivering hot water, dropping to near-zero standby. Measured kW reflects actual usage; nameplate kW reflects worst-case sizing.