UPS Battery Backup Size Calculator
Calculate the right UPS (Uninterruptible Power Supply) size for your devices.
Enter wattage to get a recommended VA rating.
UPS sizing converts the total watts of your connected devices to the required VA (Volt-Ampere) rating using a power factor.
Required VA = Total Watts / Power Factor
The standard power factor for computing equipment is 0.6–0.8. We use 0.6 for a safe margin.
Common device power consumption:
| Device | Watts |
|---|---|
| Desktop computer | 200–500 |
| Monitor (24") | 30–60 |
| Monitor (27"+) | 50–80 |
| Laptop (charging) | 45–90 |
| Router/modem | 10–20 |
| External hard drive | 10–30 |
| Inkjet printer | 30–50 |
| Laser printer | 300–600 (peak) |
| Gaming PC | 400–800 |
| NAS (2-bay) | 20–40 |
UPS sizing guide:
| VA Rating | Typical Use |
|---|---|
| 350–500 VA | Modem, router |
| 750–1000 VA | Basic PC + monitor |
| 1500 VA | Gaming PC or PC + peripherals |
| 2200 VA | Workstation + multiple monitors |
| 3000+ VA | Server or multiple workstations |
Tips:
- Never load a UPS above 80% of its rated capacity
- Higher VA rating = longer runtime during a power outage
- Line-interactive UPS is best for home/office use
- Online/double-conversion UPS is best for servers
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.