How Many Watts Is 100 VA?
A load with an apparent power of 100 VA draws 85 watts of real power at PF 0.85. For UPS and power-supply sizing, this tells you the load's watt draw, not the source's watt output: a UPS has its own manufacturer-set watt rating that is independent of its VA rating and must be checked separately on the spec sheet.
Use this citation when referencing this page.
Formula
Watts = VA × PF
Watts by Power Factor
| Load Type | PF | 100 VA = |
|---|---|---|
| Resistive (heaters, incandescent) | 1 | 100 W |
| Fluorescent lamps | 0.95 | 95 W |
| LED lighting | 0.9 | 90 W |
| Synchronous motors | 0.9 | 90 W |
| Typical mixed loads | 0.85 | 85 W |
| Induction motors (full load) | 0.8 | 80 W |
| Computers (without PFC) | 0.65 | 65 W |
| Induction motors (no load) | 0.35 | 35 W |
Using This Figure for UPS & Power Supply Sizing
Important framing. The 85W figure above is the real power a 100 VA load draws at PF 0.85. It is not the watt output of a 100 VA UPS. UPS units publish two independent ratings set by the manufacturer: a VA rating and a watt rating. A 100 VA UPS from one vendor may be rated for well under 85W continuous real power, and another 100 VA UPS may be rated for the full 100W. You cannot tell from the VA rating alone. Always check the UPS's watt rating on the manufacturer's spec sheet, and size the load to fit under both the VA rating and the watt rating.
Does Your Load Fit Under a 100 VA UPS?
Two checks, both required:
- Apparent power: add up the VA of all connected equipment. The total must not exceed the UPS's VA rating (100 VA in this example).
- Real power: add up the watts of all connected equipment. The total must not exceed the UPS's watt rating, which is a separate spec published by the manufacturer. It is often lower than 100W on budget and mid-range units.
The example table below converts each equipment type's watts into a percentage of 85W (the real-power figure at PF 0.85) as a rough steady-state comparison. It assumes the UPS's watt rating is at least 85W; if the manufacturer's watt rating is lower, the comparisons below are optimistic and the real headroom is tighter.
Example Loads (steady-state only)
| Equipment | Typical Watts | % of 100 VA at PF 0.85 |
|---|---|---|
| Desktop PC | 300W | Past 85W at PF 0.85 |
| Gaming PC | 500W | Past 85W at PF 0.85 |
| Monitor | 40W | 47.06% steady-state |
| Router + Modem | 30W | 35.29% steady-state |
| Server (inrush-sensitive) | 500W | Past 85W at PF 0.85 |
| NAS (4-bay) (inrush-sensitive) | 100W | Past 85W at PF 0.85 |
| Network Switch (PoE) (inrush-sensitive) | 150W | Past 85W at PF 0.85 |
| LED TV 55" | 100W | Past 85W at PF 0.85 |
These comparisons use steady-state wattage only. Equipment with large inrush or surge behavior, laser printer fusers, refrigerator and freezer compressors, air conditioners, sump and well pumps, shop motors, and some HVAC blowers, can momentarily draw several times their nameplate watts when they start or cycle. A UPS sized to the steady-state number alone will trip or transfer to battery on those transients. Inductive and motor loads need additional VA headroom beyond the nameplate, and laser printers specifically are usually recommended against on small consumer UPS units. Check the equipment spec sheet for inrush or starting current, or consult the UPS manufacturer's load compatibility notes.
Watts to VA (Reverse)
If you know the watts and need to find the VA rating: VA = Watts ÷ PF. A 85W load at 0.85 PF needs 100 VA minimum.
Current Draw
On an AC circuit, current is set by the apparent power (VA), not the real watts, because VA = V × I by definition. So 100 VA pulls the same amperage regardless of the load's power factor, only the real power delivered (watts) changes with PF.
| Voltage | Current (AC, any PF) | Real power at PF 0.85 |
|---|---|---|
| 120V | 0.8333 A | 85 W (see details) |
| 240V | 0.4167 A | 85 W (see details) |
Energy Cost
85W costs $0.01/hour at $0.17/kWh (rates last reviewed April 2026), or $3.47/month (8h/day). Full breakdown.
Common UPS Sizes
How does a 100 VA load compare to standard UPS ratings? The watts columns below convert each UPS's VA rating to a load-side watt figure at two power factors. These are not the UPS's watt ratings. UPS watt ratings are published separately by the manufacturer and are often lower, especially on older and budget units. Use the columns below to compare a load's real power draw to the UPS's VA rating, then check the UPS's spec sheet for its watt rating independently. The use-case column is reference context only; rack and server picks usually need extra VA and PF headroom beyond the steady-state column to absorb inrush at startup and motor-load cycling.
| UPS VA Rating | Load watts at PF 0.85 | Load watts at PF 0.65 | Typical Use |
|---|---|---|---|
| 350 VA | 297.5W | 227.5W | Router and cable modem, always-on |
| 500 VA | 425W | 325W | Single desktop PC at idle |
| 750 VA | 637.5W | 487.5W | Desktop PC plus a monitor |
| 1,000 VA | 850W | 650W | Workstation with peripherals |
| 1,500 VA | 1,275W | 975W | Single rackmount server (plus inrush headroom) |
| 2,200 VA | 1,870W | 1,430W | Two or three PCs or a small workgroup |
| 3,000 VA | 2,550W | 1,950W | Small server rack (plus inrush and PF headroom) |
| 5,000 VA | 4,250W | 3,250W | Small data closet (plus inrush and PF headroom) |
| 10,000 VA | 8,500W | 6,500W | Full server rack (plus inrush and PF headroom) |