Router / Modem Backup Runtime Calculator
Estimate how long a UPS or portable power station can keep your modem, router, fiber ONT, Wi-Fi access point, and small network switch online during an outage.
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Fast Rule
A 20W internet load on a 512Wh power station is roughly 21.8 hours after efficiency losses. A 50W setup on the same station is closer to 8.7 hours.
Measure watts when possible. Router and modem labels often show maximum adapter output, not real wall draw.
Your Network Load
How To Use The Estimate
This calculator is best for low-watt internet gear. If you add a NAS, desktop, monitor, or large PoE switch, measure the load with a wall power meter and use the Homelab Power Calculator for the broader setup.
| Result | What It Usually Means |
|---|---|
| Under 4 hours | Fine for brief outages, but too small for work-from-home reliability. |
| 4 to 12 hours | Good for many router/modem setups and short daytime outages. |
| 12 to 24 hours | Strong home internet backup range for fiber or cable internet gear. |
| 24+ hours | Useful for longer outages, especially if paired with solar input or a second battery. |
New: if you want the quick runtime math before choosing capacity, read How Long Can a Portable Power Station Run a Router?. To choose a station size from your target hours, use the Portable Power Station Size Calculator.
Frequently Asked Questions
What devices should I include in router backup runtime?
Include the modem or fiber ONT, router, Wi-Fi access point, small switch, and any other device required for internet access.
Why is usable watt-hours lower than battery capacity?
UPS units and power stations lose energy to inverter overhead, conversion loss, battery reserve, and load behavior. A conservative efficiency estimate gives more realistic runtime.
Can a portable power station replace a UPS for a router?
Sometimes, but check pass-through behavior and switchover time. A true UPS is usually safer when the network cannot blink during a short outage.
New: for choosing a power station class after calculating runtime, read Best Power Station for Internet Outage.
Related hub: How to Keep Your Internet Online During a Power Outage.