UPS runtime calculator
A UPS gives you minutes to save your game and shut down after a power cut. Enter the battery capacity and your load to estimate runtime, and check you are not asking more than the unit can deliver.
How UPS runtime is estimated
A UPS stores energy in a battery and converts it to mains power through an inverter. The energy available is the battery capacity in watt hours, less what is lost in the inverter and what is held back to protect the battery. Divide that usable energy by your load in watts and you have the runtime in hours. For example, a 360 watt hour battery at 85 percent efficiency with 80 percent usable can supply about 245 watt hours, which runs a 300 watt load for roughly 49 minutes.
Real runtime is shorter at heavy loads because batteries deliver less energy when drained quickly, and it shortens as batteries age. Treat the result as a guide and compare it with the runtime chart in the maker data sheet.
Example runtimes for common battery sizes
These runtimes use 85 percent inverter efficiency and 80 percent usable battery. Your unit may differ.
| Battery | 200 W load | 400 W load | 600 W load |
|---|---|---|---|
| 200 Wh | 41 min | 20 min | 14 min |
| 360 Wh | 73 min | 37 min | 24 min |
| 600 Wh | 122 min | 61 min | 41 min |
| 1000 Wh | 204 min | 102 min | 68 min |
VA, watts and the power factor
UPS units are sold by volt-amp rating, but computers draw real power in watts. The two differ by the power factor, so a 1500 VA unit with a 0.6 factor delivers about 900 watts. Many modern units have higher power factors, often 0.9 or more, so always check the data sheet. A gaming PC with a high-end graphics card can draw several hundred watts, so a small 600 VA unit may be overloaded the moment a game starts.
This tool checks your load against the maximum output and warns when you exceed it. It also helps you decide how large a unit you need for your desired runtime, using the table of runtimes at different loads.
What a gaming UPS is for
The goal of most home setups is not hours of gaming during a blackout. It is a few safe minutes to save your progress and shut the machine down, protecting files and hardware from sudden power loss and brief dips. Five to ten minutes at your gaming load is a sensible target. Longer runtimes need much larger batteries, which cost far more.
Many people add a UPS only for the PC and monitor, with the router on its own small unit. To size the PC load properly, use the PSU wattage calculator, and see how much your system costs to run with the electricity cost calculator.
How to use the uPS runtime calculator
- Find the battery capacity in watt hours on the UPS data sheet.
- Measure or estimate your gaming load in watts, including the monitor.
- Leave efficiency at 85 percent and usable battery at 80 percent unless the maker states otherwise.
- Enter the VA rating and power factor to check the load is within limits.
- Compare the runtime with the time you need to save and shut down.
Common mistakes to avoid
- Plugging a laser printer or heater into the UPS, which can overload it.
- Using the power supply wattage as the load instead of real draw.
- Expecting full runtime from an old battery.
Related tools and guides
Keep going with these: PSU wattage calculator, electricity cost calculator, gaming PC heat output calculator, PSU efficiency calculator, 1000W to 1300W PSU guide.
Frequently asked questions
How long will a UPS run my gaming PC?
Divide usable battery energy by your load. A 360 watt hour UPS with typical losses can run a 300 watt gaming load for roughly 45 to 50 minutes in theory, but real figures are shorter. Check the manufacturer runtime chart for your exact load.
What size UPS do I need for a gaming PC?
Pick one whose output rating is comfortably above your real peak draw, plus the monitor. A single high-end graphics card build often needs a unit rated at least 1000 to 1500 VA. Check the watt rating, not just the VA figure.
Is a UPS good for gaming PCs?
It protects against blackouts and brief dips, giving you time to save and shut down. It is not meant to keep gaming for long. Choose a unit with enough output for your peak load and consider an online or line-interactive design.
What is the difference between VA and watts on a UPS?
VA is apparent power and watts is real power. Watts equal VA times the power factor. A 1500 VA unit with a 0.6 power factor supplies 900 watts. Always check the watt rating when matching a UPS to a PC.
Does a UPS battery wear out?
Yes. Most sealed lead-acid batteries need replacing every three to five years, and capacity falls over time. Runtime drops as they age. Test your unit occasionally and replace the battery when runtime is much shorter than when it was new.
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