Generator kVA to Amps Calculator
Full-load amps for any generator rating — pick a standard genset size or type your own. The result is the current the alternator can carry continuously at that voltage, the number breakers and changeover switches are sized from.
Balanced three-phase load, line-to-line voltage. Change any value and the result updates instantly.
Reading a genset rating
A generator's headline number is apparent power — kVA — because that is what the alternator physically delivers: a voltage and a maximum current. The general kVA to amps calculator does the same conversion without the genset framing; this page adds the standard sizes and the rating classes.
kVA on the plate, kW in the brochure
Many diesel gensets are also quoted in kW, conventionally at a power factor of 0.8: a 100 kVA set is sold as an "80 kW generator". The 0.8 belongs to that kW figure only. The current depends on kVA and voltage alone — putting the 0.8 into the amps formula is the classic mistake that overstates full-load current by 25%, and it is why this calculator never asks for a power factor.
Standby, prime and continuous ratings
The same machine can carry different kVA headlines for different duties: standby (emergency, limited hours, no overload), prime (variable load, unlimited hours, usually a 10% overload allowance for limited periods) and continuous (steady load, unlimited hours). Full-load amps follow whichever rating you are planning against — check the data plate's class before treating the figure as a continuous ceiling.
Full-load amps and breakers
Full-load amps (FLA) is the alternator's rated continuous current at the stated voltage and phase. It is the anchor for three practical decisions: the generator's own output breaker, the changeover or transfer switch rating, and the cable size between set and panel (with the usual code derating on top). A load whose running current exceeds the FLA will trip protection or cook windings; a load with heavy motor starting may need headroom well beyond its running amps, because the set must supply the start surge without its voltage collapsing.
Remember that three-phase FLA is per phase. A 62.5 kVA set at 400 V gives 90.21 A on each of the three lines — not three times that in total usable single-phase current unless the loads are spread evenly across phases.
Generator standard sizes — full-load amps
The common genset and DG ratings with their full-load amps at the voltages they are usually connected to. Every value is computed from the rating, not copied from a manufacturer's chart.
| Generator (kVA) | 240V · single-phase | 400V · three-phase | 480V · three-phase |
|---|---|---|---|
| 10 | 41.67 A | 14.43 A | 12.03 A |
| 20 | 83.33 A | 28.87 A | 24.06 A |
| 30 | 125.00 A | 43.30 A | 36.08 A |
| 50 | 208.33 A | 72.17 A | 60.14 A |
| 62.5 | 260.42 A | 90.21 A | 75.18 A |
| 100 | 416.67 A | 144.34 A | 120.28 A |
| 125 | 520.83 A | 180.42 A | 150.35 A |
| 200 | 833.33 A | 288.68 A | 240.56 A |
| 250 | 1,041.67 A | 360.84 A | 300.70 A |
| 400 | 1,666.67 A | 577.35 A | 481.13 A |
| 500 | 2,083.33 A | 721.69 A | 601.41 A |
| 750 | 3,125.00 A | 1,082.53 A | 902.11 A |
| 1000 | 4,166.67 A | 1,443.38 A | 1,202.81 A |
Worked examples
A 20 kVA DG set on a 415V supply (the standard across much of South Asia): 20,000 ÷ (√3 × 415) = 27.82 A per phase. A 40 A-class main breaker covers the set's full output with room for the usual tolerances.
A 125 kVA rental generator at 480V three-phase delivers 125,000 ÷ (√3 × 480) = 150.35 A per phase — the figure the rental yard's cable and distro sizing starts from.
A 30 kVA home standby set at 240V: 30,000 ÷ 240 = 125.00 A. Against a 200 A house service that is roughly 60% of the panel's capacity — plenty for managed loads, not for everything at once.
Frequently asked questions
How many amps can a 20 kVA generator produce?
At 240 V single-phase, a 20 kVA generator’s full-load current is 83.33 A. At 400 V three-phase it is 28.87 A per phase. These are the alternator’s rated limits — the breaker on the set may be smaller, and continuous running is usually planned below the full figure.
What is full-load amps (FLA) on a generator?
Full-load amps is the current the alternator can deliver continuously at its rated kVA and voltage — the figure this calculator produces. It is the ceiling for the loads you connect, and the starting point for sizing the breaker and cable between the generator and the panel. Manufacturers also state it on the data plate, sometimes as "rated current".
Why are generators rated in kVA and not kW?
The alternator’s limits are set by current (winding heating) and voltage (insulation), and current × voltage is apparent power — kVA. The real power in kW depends on the load’s power factor, which the generator maker does not control. A kVA rating is therefore the honest, load-independent number; the engine’s kW output is quoted separately, commonly at a reference power factor of 0.8.
What does DG mean in generator sizes?
DG is short for diesel generator (or diesel genset), the term used across India, Pakistan and much of Asia and Africa for a diesel engine + alternator set. A "20 kVA DG" is a 20 kVA diesel generator, and its full-load amps follow exactly the same formulas — 83.33 A at 240 V single-phase or 28.87 A at 400 V three-phase.
Can a generator run at its full-load amps continuously?
It depends on the rating class. Standby-rated sets are sized for limited hours at full load; prime and continuous-rated sets are built to run at or near full load indefinitely, usually with a stated overload margin. The data sheet’s rating class — not the kVA headline — decides. For long runs, most engineers plan around 70–80% of the full-load figure.
Sources and references
Full-load current follows the same standards-based identities as the main converter; rating-class terminology follows common manufacturer practice described in the methodology notes.
- NFPA 70 — National Electrical Code (NEC) — the code electricians size conductors and protection against
- IEEE Std 141 — Recommended Practice for Electric Power Distribution (Red Book) — apparent power and load-current practice for industrial and commercial systems
- IEC 60038 — Standard Voltages — the standard voltage levels (120, 208, 240, 400, 480 V) used across this site
- NIST — SI unit of electric current (the ampere) — the definition of the ampere behind every result