kW vs kVA for UPS Sizing: Formula, Examples and Calculator
kW measures real power; kVA measures apparent power. Their relationship is kW = kVA × power factor. To shortlist a UPS, check both output ratings against the load. Converting between them does not calculate battery runtime or establish the right installation design.
How to convert kW to kVA
Eaton explains power factor as the ratio connecting watts and volt-amperes. The same relationship applies to kilowatts and kilovolt-amperes because both units are divided by 1,000: kVA = kW ÷ power factor. Use a positive power factor no greater than 1 for this conversion.
For example, an assumed 72 kW load at a power factor of 0.9 corresponds to 80 kVA: 72 ÷ 0.9 = 80. At 0.8, that same real-power load corresponds to 90 kVA. These are arithmetic examples, not measured characteristics of a particular server or UPS.
| Assumed load power factor | Apparent power required | Calculation |
|---|---|---|
| 1.0 | 72 kVA | 72 ÷ 1.0 |
| 0.9 | 80 kVA | 72 ÷ 0.9 |
| 0.8 | 90 kVA | 72 ÷ 0.8 |
Check two output limits, not one marketing number
Consider two hypothetical configurations: A is rated 100 kVA / 90 kW; B is rated 100 kVA / 100 kW. For an assumed 95 kW, unity-power-factor load, both appear large enough if you look only at kVA. The 95 kW load nevertheless exceeds Configuration A’s 90 kW limit. Configuration B passes these two basic numerical checks, but that alone does not approve it for the project.
Now consider an assumed 85 kW load at 0.8 power factor. It requires 106.25 kVA, so neither 100 kVA configuration passes the apparent-power check. The practical buying lesson is to carry kW and kVA in separate spreadsheet columns throughout the comparison. Ask the manufacturer to confirm allowable operation for the actual load characteristics.
Keep load power factor separate from UPS input power factor
The power factor used to convert your equipment load belongs to that load. A UPS specification can also report input power factor, describing the UPS on the supply side. ENERGY STAR labels its measured input-power-factor fields separately from active and apparent output ratings.
Do not copy an input power factor from a UPS brochure into a calculation for the equipment connected to its output. Label every value with what it describes: measured critical load, assumed future load, UPS input, or UPS output capacity. If your worksheet simply says PF without context, ask for the missing context before comparing bids.
Capacity and runtime answer different questions
Eaton separates capacity, the power a UPS can support, from runtime, the duration it can support a specified load on its battery system. A larger kW rating is therefore not a promise of a particular number of backup minutes.
Write your requirement as two statements: the load envelope that needs support, and the required duration under specified conditions. For example, 72 kW today with a separately documented growth plan, plus a supplier-validated runtime requirement at that load. Request the proposed battery configuration and supporting runtime data with the quote. Leave runtime blank when you do not have that evidence; do not manufacture it from a kVA label.
Sources: Eaton: UPS sizing guide ↗
Build a load worksheet the supplier can actually review
Before shopping by capacity, create a short evidence pack. Give each figure an owner and a date so that a later equipment refresh does not silently invalidate the comparison. Keep current operation separate from planned additions; adding both into an unexplained total makes it harder to challenge assumptions.
Ask your project designer and supplier to determine appropriate allowance for growth, transient behavior and redundancy. A universal percentage cannot represent every project. Eaton explicitly treats growth and redundancy as sizing considerations; your quotation should state what the proposed configuration can support when an identified unit or module is unavailable.
- Equipment list: identify the loads included and explicitly excluded.
- Load evidence: record kW, kVA or power factor, measurement conditions and date.
- Future additions: distinguish approved equipment from speculative growth.
- Availability requirement: state the failure or maintenance condition the design must accommodate.
- Battery requirement: request runtime evidence for the exact proposed load and configuration.
Sources: Eaton: UPS sizing guide ↗
Use the calculator, then verify the product configuration
The calculator on this page performs the unit conversion using your inputs. It does not choose a UPS, assess a distribution system or validate an electrical installation. Save its result with the assumptions rather than treating the output as a purchase recommendation.
Power Field Guide displays the minimum tested active and apparent output ratings imported from the ENERGY STAR dataset. A family name or modular cabinet description may cover other configurations. Open the source record and obtain the current manufacturer datasheet for the exact configuration being quoted. The useful next step is a shortlist with documented unknowns, followed by a supplier response that resolves them.
Real power → apparent power
Conversion only. This does not size redundancy, runtime, protection or installation requirements.
Common questions
Is 100 kVA equal to 100 kW?
Only at a power factor of 1.0. At 0.9, 100 kVA corresponds to 90 kW. Separately confirm the UPS configuration’s published kW and kVA limits.
Can I calculate UPS runtime from kVA?
No. Capacity alone does not establish runtime. Request battery and runtime data at the intended load for the proposed configuration.
Sources: Eaton: UPS sizing guide ↗
Which power factor belongs in the calculator?
Use the power factor of the load being converted. Do not substitute the UPS input power factor or assume an unknown load has a value of 1.0.
Sources: Eaton: The difference between VA and Watts ↗ · ENERGY STAR: AC Output UPS reporting template ↗
Does passing the kW and kVA checks mean the UPS is suitable?
It passes only an initial capacity screen. The project still needs confirmation of voltage, configuration, battery runtime, operating conditions and the required availability arrangement.
Sources and editorial scope
Published by Power Field Guide using the primary sources below and original procurement examples. Manufacturer and provider statements are attributed to their source. Examples are illustrative; this guide is not a site design or confirmation of equipment availability.
- Eaton: The difference between VA and Watts ↗Checked 2026-09-12
- Eaton: UPS sizing guide ↗Checked 2026-09-12
- ENERGY STAR: AC Output UPS reporting template ↗Checked 2026-09-12