kW vs kVA vs kWh: Three Letters Apart, Worlds of Confusion
By the VoltConvert team · June 12, 2026
Three units share the kilowatt family name, and mixing them up costs real money — undersized generators, oversized bills, transformer capacity left on the table. Here's the clean separation, with the formulas behind each.
kW: the work actually getting done
Kilowatts measure real power — the rate at which electricity becomes heat, light or motion. Your 1.5 kW kettle, a 7.2 kW EV charger, an 11 kW heat pump: all statements about useful work per second. When you total up a building's loads, you're adding kW.
kVA: what the supply must actually carry
Kilovolt-amps measure apparent power — voltage times current, with no questions asked about how much of that current does useful work. Wires, transformers and generator windings heat up according to current, so their capacity is rated in kVA. The two units are joined by power factor: kW = kVA × PF. Since real-world mixed loads run at PF 0.7–0.95, the kVA figure is always the bigger number — and that gap is exactly why a "100 kVA" generator delivers about 80 kW at the industry-standard 0.8 PF rating point. The conversions both ways live here: kW to kVA and kVA to kW.
kWh: power sustained over time
Kilowatt-hours measure energy — kW multiplied by hours. This is the unit your meter spins in and your utility bills for. A 2 kW heater running 3 hours consumes 6 kWh; at a typical US residential rate near $0.17/kWh, that evening of warmth costs about a dollar. The everyday confusion — "my generator is 5,000 watts, so how many kWh is that?" — dissolves once you see kW as a speed and kWh as a distance. The kWh to kW calculator moves between them.
Why generators and transformers refuse to speak kW
Because they can't know your power factor in advance. A generator's windings are limited by current regardless of whether that current does useful work, so the honest rating is kVA. The kW you can extract depends on what you plug in: a resistive load (PF ≈ 1) can take nearly the full kVA as real power; a workshop of old induction motors at PF 0.75 leaves a quarter of the capacity unusable. This is also why utilities charge large commercial customers for poor power factor — low-PF loads hog grid capacity without paying for it in kWh.
The homeowner's worked example
Storm season, US suburb. Essential loads: refrigerator 700 W, furnace blower 800 W, lights and electronics 400 W, sump pump 600 W — call it 2.5 kW running. Convert to apparent power at PF 0.8: 3.1 kVA. Add surge headroom for the largest motor start (sump pumps briefly demand 3–5× running watts) and the sensible purchase is a 5 kVA-class generator, not the 3 kVA unit the raw kW total suggested. Two unit conversions just prevented a flooded basement. The single-phase kW to kVA calculator walks the same path.
Keep them straight forever
kW = work being done now. kVA = capacity the supply must carry now. kWh = work accumulated over time. Equipment is bought in kVA, loads are planned in kW, and money changes hands in kWh. Once those three sentences settle in, every spec sheet in the electrical aisle becomes readable.