UPS runtime calculator
Estimate runtime for a UPS or DIY battery bank powering a router, modem, PC or home lab.
1. Battery
Series packs add voltage; parallel packs add Ah. Enter the total pack voltage and total Ah if unsure, with 1 battery.
Assumption: not every battery can be fully discharged without damage. Check your battery’s datasheet.
Assumption — planning figure.
2. Load
3. Check against UPS rating (optional)
Assumption: 0.6 is a conservative placeholder. Power factor varies by model — use the watt rating on your UPS label.
Appliance wattages used by this calculator
The same sourced figures the calculator uses (also in plain HTML). Ranges are shown in full; the calculator uses the upper end. Starting watts = total watts while a motor starts. Full chart with notes.
| Appliance | Running W | Starting W | Basis | Source |
|---|---|---|---|---|
| Television, flat-screen 20" | 120 | 120 | approx. | Honda Power Equipment |
| Television, flat-screen 46" | 190 | 190 | approx. | Honda Power Equipment |
| Laptop computer | 200–250 | 200–250 | approx. | Honda Power Equipment |
| Desktop computer | 600–800 | 600–800 | approx. | Honda Power Equipment |
| Monitor (LCD) | 30 | 30 | approx. | Honda Power Equipment |
| Printer | 400–600 | 400–600 | approx. | Honda Power Equipment |
| Radio | 50–200 | 50–200 | approx. | Honda Power Equipment |
| Internet router / modem | 10–20 | — | approx. | Champion Power Equipment |
| Phone / laptop charger | 20–100 | — | approx. | Champion Power Equipment |
| Home security system | 15–40 | — | approx. | Champion Power Equipment |
| CPAP machine (no heated humidifier) | 30–60 | — | approx. | Champion Power Equipment |
| CPAP machine (heated humidifier) | 60–120 | — | approx. | Champion Power Equipment |
| LED light bulb (each) | 8–15 | — | approx. | Champion Power Equipment |
| Wi-Fi access point (not PoE-powered) | 6–12 | — | estimate | RACKDENSITY |
| Switch, 8-port unmanaged | 4–5 | — | estimate | RACKDENSITY |
| Router / firewall appliance | 12–18 | — | estimate | RACKDENSITY |
| Mini PC, Intel N100-class (light load) | 8–10 | — | estimate | MiniPCLab |
| Mini PC, 6–8 core | 12–50 | — | estimate | RACKDENSITY |
| NAS, 4 bays, HDDs spinning | 30–45 | — | estimate | RACKDENSITY |
How it works
Runtime (h) = battery Wh × usable fraction × inverter efficiency ÷ load W, where battery Wh = volts × amp-hours.
- Device wattages in the picker come from the sourced wattage chart; home-lab rows are estimates — measure your own gear with a plug-in power meter for better accuracy.
- A UPS bridges short outages and gives you time to shut down gracefully; it is not a substitute for a generator or power station in a long outage.
- Runtime shrinks as batteries age. This tool is a simple estimate — not a replacement for the manufacturer’s runtime chart.