Free tool
UPS Battery Backup Runtime Calculator
How long will a battery backup keep your laptop, monitor and router running in a power outage? Tick your devices, enter the battery size, and get an estimate plus the minimum UPS size to look for.
This free tool estimates how many minutes a battery backup, an uninterruptible power supply (UPS), keeps your chosen devices running in an outage, and the minimum UPS size to look for. Pick the devices on your desk, enter the UPS rating and see whether it covers a long enough save-and-shut-down window.
What it does
Estimates how many minutes a battery backup keeps your chosen devices running, and the minimum UPS size to look for.
Who it helps
Anyone who works from home where outages happen and needs the router, modem and computer to survive one.
How to use it
- Tick the devices you need during an outage.
- Enter the battery size (Wh or VA).
- Read the estimated runtime.
- Check the suggested minimum UPS size.
What do you need to keep running?
Typical watts. Check the label on your device and change the number if it differs.
Your UPS battery
Battery watt hours are on the spec sheet (for example 12 V x 9 Ah = 108 Wh per battery). If you only know the VA rating, switch the button above; we estimate the battery at about 0.5 Wh per VA, labeled estimate.
Estimated backup
About 1 hour 27 minutes: enough to finish a call and shut down properly.
Runtime = battery Wh x 0.85 (inverter losses) / total load W x 60. UPS size (rule of thumb) = load W / 0.6. Real runtime varies with battery age, temperature and load: expect less from an older battery.
What your result means
- Runtime under 10 minutes: enough to save work and end a call, not to keep working.
- Laptop plus router and modem usually runs the longest, because the laptop has its own battery.
- A desktop with two monitors drains a small UPS fast. Size up or leave the monitors off the UPS.
- The suggested VA is a rule of thumb. Check the maker’s runtime chart before you buy. Read the guide
How it works
Estimated runtime (minutes) = battery Wh x 0.85 / total load W x 60. The 0.85 allows for inverter losses. Suggested minimum UPS size: VA = total load W / 0.6, a common rule of thumb that assumes a 0.6 power factor. When you only know the VA rating, the battery is estimated at about 0.5 Wh per VA, which varies by model. Real runtime depends on battery age, temperature and how the load changes, so treat the result as an estimate.
Sources
- Runtime and sizing formulas are rules of thumb used across UPS makers’ guidance; labeled estimate
- Device watt presets: typical values; check the label on your device
FAQ
Do I need a UPS for a laptop?
A laptop has its own battery. A small UPS is still useful to keep the router and modem up, so your calls and WiFi survive a short outage.
What size UPS for a desktop and two monitors?
Add the watts (for example 200 + 30 + 30 = 260 W) and divide by 0.6: about 450 VA minimum. Bigger gives more minutes.
Why is my real runtime shorter than the estimate?
Batteries lose capacity with age and heat, and some devices draw more than their label at startup. Replace the battery every 3 to 5 years.