kW vs kVA on a UPS: what the power factor changes

Watts, volt-amps and power factor

Schneider Electric's White Paper 15 sets out the two measures. The power in watts is the real power drawn by the equipment; volt-amps are the apparent power, the voltage applied times the current drawn. The watt rating decides the power bought from the utility and the heat the equipment gives off, while the VA rating is used for sizing wiring and circuit breakers. The ratio of watts to VA is the power factor, written as a number such as 0.7 or a percentage such as 70%.

The load side matters as much as the UPS. WP 15 explains that IT equipment uses switching power supplies of two kinds. Power factor corrected (PFC) supplies have equal watt and VA ratings, a power factor of 0.99 to 1.0, and large equipment such as servers, routers, switches and drive arrays made after about 1996 uses them. Capacitor input supplies, typical of personal computers, draw watts of 0.55 to 0.75 times their VA. WP 15 (2011) adds that for larger UPS it was becoming common to focus on the watt rating and to give equal watt and VA ratings, because the typical loads have equal ratings. Makers still publish both: the table below includes 0.9 models.

A UPS has a maximum watt rating and a maximum VA rating, and WP 15 is explicit that neither may be exceeded. For small UPS designed for computer loads that publish only a VA rating, WP 15 says it is appropriate to assume a watt rating of 60% of the VA figure; every family in the table below publishes its kW. For loads with a low power factor and for harmonics, see harmonics and power factor.

Output power factor by family

kW = kVA × output power factor. The table gives each family's rating as its maker publishes it; the right-hand column is kW per kVA.

Several of these lines are 400 V products: Delta lists the Ultron DPS at 220/380 to 240/415 V, the Delta DPH 300 to 600 kVA models come in 380 to 415 V frames, and Tripp Lite lists the SVTX, SUTX and SVX among its 400 V families. Check the voltage table before choosing.

XPC M90U-80, Delta Ultron DPS, Mitsubishi 9900B and Tripp Lite figures are from their product pages and brochures, checked 11 October 2026; the others are from this site's specification tables, read from each maker's page on 3 October 2026.

How to size a three-phase UPS

Worked example. Eaton rates the 9355 at a 0.9 output power factor, so its 30 kVA model delivers 27 kW. Eaton's base growth multiple is 1.2; applied to that kW rating, 27 kW ÷ 1.2 = 22.5 kW is the most measured load today that keeps the margin. A unity-rated 30 kVA UPS delivers 30 kW, and the same rule gives 25 kW. Redundancy comes on top, and the kVA still has to be checked. Same kVA badge, two different answers.

For redundancy designs, see N, N+1 and 2N; for each current family's range in kW, see sizing a three-phase UPS.

Canadian voltages: 208, 480 and 600 V

All eight families in the table below are listed at 208 V, 480 V or both. For a 600 V supply, Eaton offers the Power Xpert 9395P as a native 600 V UPS; the Eaton 9355 and the Tripp Lite S3M reach 600 V with an input isolation transformer.

Voltages as listed by each maker for North America, read 3 October 2026. A family missing from the table may still have a 600 V option; the full comparison is in 600 V three-phase UPS in Canada.

Replacing an older UPS

A like-for-like kVA replacement can hide a kW change. Tripp Lite puts it plainly for the SVX: because it is rated at unity power factor, it may be sized for actual power and load requirements. When a UPS rated below unity is replaced by a unity model of the same kVA, the new one delivers more kW; when the new model is rated at 0.9, the kW must be checked against the measured load.

Breakers, cables and the electrician

WP 15 notes that, for equipment drawing power, the VA rating rather than the watt rating is used for sizing wiring and circuit breakers. For the UPS's own input, bypass and output breakers and cables, ask the electrician, who also handles any transformer.

Getting the sizing done

Load studies and system selection are part of a UPS sizing and installation consultation, and a first estimate can be worked out with the step-by-step sizing guide.

Related pages

Common questions

What is the difference between kW and kVA on a UPS?

kVA is the apparent power rating (volts times amps); kW is the real power the UPS can deliver. kW = kVA × output power factor.

How many kW is a 30 kVA UPS?

It depends on the output power factor: 30 kW at unity and 27 kW at 0.9. Eaton rates its 30 kVA 9355 at 27 kW, and Tripp Lite its 30 kVA SVTX, a 400 V model.

Should I size a UPS in kW or kVA?

On kW first, from the load plus growth, then check the kVA. A UPS has both ratings and neither may be exceeded.

Why can a new UPS of the same kVA carry more load than the old one?

A unity-rated UPS delivers as many kW as kVA, so it carries more real load than a 0.9 model with the same kVA rating. Tripp Lite notes that a unity-rated SVX may be sized for actual power.

Do I need a transformer for a 600 V supply?

It depends on the model. Eaton offers the Power Xpert 9395P as a native 600 V UPS with no external transformer; the Eaton 9355 and the Tripp Lite S3M reach 600 V with an input isolation transformer. At 480 V, the Eaton 9355 also uses an input isolation transformer, and XPC lists a 480 V input transformer as an option for the 208 V M90U-80. For models with no 600 V listing, the 600 V guide covers the options.

Do I need an electrician to size the breaker and cables for a three-phase UPS?

Yes. Leave the input, bypass and output breakers, the cables and any transformer to the electrician. WP 15 notes only that, for equipment drawing power, the VA rating rather than the watt rating is used for sizing wiring and breakers.

Send us the details

Fill this in and your own mail client opens with everything already written out. Nothing is sent from this site.