UPS Sizing: VA vs Watts and What Size You Need
Size a UPS by watts first; the VA number is apparent power and is always at least as high as the watt rating, so a UPS must cover your gear on both numbers.
By Damien VolkmanContributing writer.
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The short answer
A UPS (uninterruptible power supply) keeps a computer, router or other gear running on battery for a few minutes when the power fails, long enough to save work and shut down. To size one:
- Add up the watts your devices draw. The label or the power supply rating gives a maximum.
- Pick a UPS whose watt rating is above that total, with room to spare.
- Check that the VA rating also covers the load.
- Check the runtime chart for how many minutes you get at your load.
Of the 595 UPS battery backups listed on Wiki Shopping on October 26, 2026, the most common VA rating is 1500 VA, with 75 units.
What does VA mean on a UPS?
VA stands for volt-amperes: the voltage times the current flowing to the load. That is called apparent power. Watts measure real power, the energy the devices actually use. The two are linked by the power factor:
Watts = VA x power factor
The power factor is between 0 and 1 for ordinary loads, so the watt figure is never higher than the VA figure. Many UPS makers state both. Each is a separate limit: the VA rating is set by the most current the UPS can safely carry, the watt rating by how much power it can handle, and neither may be exceeded.
VA vs watts for computers
Modern computer power supplies have a high power factor. Energy Star calls for a power factor of at least 0.9 at full output in a computer's power supply, and supplies with active power factor correction reach up to 0.99. Supplies without any correction sit around 0.55 to 0.65, which means they need noticeably more VA for the same watts.
As an example of the arithmetic, 450 W of gear at a power factor of 0.9 is 500 VA (450 divided by 0.9). The same 450 W at 0.6 would be 750 VA.
Common UPS sizes on Wiki Shopping
| VA rating | UPS units |
|---|---|
| 500 VA | 12 |
| 1000 VA | 27 |
| 1500 VA | 75 |
| 3000 VA | 18 |
| 6000 VA | 15 |
| 10000 VA | 17 |
On Wiki Shopping, 75 units are rack form and 55 are tower form.
Runtime and design
- Runtime: most units run on battery for about 5 to 15 minutes. Runtime depends on the load, so makers publish runtime in minutes at different loads; check it at your own total.
- Standby and line-interactive: run gear on wall power and switch to battery when the voltage goes out of range. A line-interactive unit also corrects low or high voltage without using the battery. 54 units on Wiki Shopping are line-interactive.
- Online (double conversion): always runs the load through its inverter, isolating gear from power problems. 85 units are online.
- Output wave: cheaper units can put out a stepped wave close to a square wave; better ones produce a nearly pure sine wave. 95 units list pure sine wave output.
How we count
UPS counts are Wiki Shopping filter pages, read from our database on October 26, 2026. A unit counts when its store listing states the VA rating, form, design or feature. The VA examples are our arithmetic from the formula above.
Shop by spec
UPS Battery Backups
5000 VA, 4250 Watts, rack
- 5000 VA/4250 W - 208 V AC - 3U rack-mountable - 2, 2 x NEMA L6-20R, NEMA L6-30R
- Receptacles: 2 x NEMA L6-20R, 2 x NEMA L6-30R
- Load capacity: 5000 VA/4250 W
- Input Voltage: 208 V AC
- Output voltage: 208 V AC
- Typical battery recharge time: 1.50 hour
- Rack height: 3U
- Form Factor: Rack-mountable
- Weight (Approximate): 123 lb
- Environmental Certification: RoHS, energy Star, reach
1500 VA, 850 Watts, Line interactive, 8 Outlets
- STABLE POWER SUPPLY: The AVR stabilizes output power during fluctuations, extends battery life, and provides clean power to connected devices.
- USER-REPLACEABLE BATTERIES: Users can easily replace and purchase batteries directly from Vertiv to safely extend UPS life.
- CONVENIENT RUNTIME LED INDICATORS: Four LED indicators provide a quick view of remaining battery capacity.
- THREE-YEAR WARRANTY: This UPS comes with a full-unit coverage and an advanced replacement warranty for three years.
- EASIER ALARM MANAGEMENT: A dedicated mute button allows users to silence loud UPS alarms once problems that activated them have been resolved.
1500 VA, 900 Watts, 10 Outlets
- 1500VA / 900W RELIABLE BACKUP POWER: The highest VA capacity available for home use; delivers short-term battery power to keep essential devices powered during blackouts, surges, and unexpected power interruptions
- TEN PROTECTED OUTLETS: Power your entire setup with 5 battery backup outlets for essential devices, and 5 surge-only outlets for peripherals. Plus built-in coaxial and Ethernet surge protection for added peace of mind
- AUTOMATIC VOLTAGE REGULATION (AVR): Corrects low voltage brownouts (88V+) and surges (+/-13%) without draining battery. Boosts or trims to stable 120V. Extends runtime for blackouts; Active PFC compatible for gaming PCs
- REPLACEABLE BATTERY & ENERGY STAR UPS: User-replaceable battery (APCRBC124, sold separately) for zero-downtime swaps. ENERGY STAR certified for 92%+ efficiency, cutting energy costs vs standard UPS units
- LCD DISPLAY PANEL: Features an intuitive LCD screen that displays real-time status information including battery charge level, estimated runtime, load capacity, and input voltage for easy monitoring of your power protection system
2200 VA, 1650 Watts, 10 Outlets
- 2200VA/1650W Smart App Sinewave Battery Backup Uninterruptible Power Supply (UPS) System uses sine wave output to support Active PFC & conventional power supplies; OPTIONAL SNMP/HTTP remote monitoring with RMCARD205 sold separately
- NINE IEC-320 C13 AND ONE IEC-320 C19 OUTLETS: Provide battery backup and surge protection to safeguard corporate and network servers, telecom installations, and VoIP systems; INPUT: IEC-320 C20 plug with 10 foot power cord
- ROTATABLE MULTIFUNCTION LCD PANEL: Displays immediate, detailed information on battery and power conditions, including: estimated runtime, battery capacity, load capacity, etc. whether rack mounted or standing as a tower
- AUTOMATIC VOLTAGE REGULATION (AVR): Corrects minor power fluctuations without switching to battery power, thereby extending the life of the battery; HIGH VOLTAGE INPUT: 220V, 230V, or 240V selectable input voltage
- 3-YEAR WARRANTY – INCLUDING THE BATTERIES; $400,000 Connected Equipment Guarantee and FREE PowerPanel Business Edition Management Software (Download)