Power Station Runtime Calculator
Wondering how long your power station will run a specific device? Enter its wattage and your power station's capacity below to find out — the same formula used throughout our sizing guides, done for you instantly.
The Formula Behind This Calculator
Runtime is your power station's usable energy divided by how much power your device draws. We apply a standard 85% inverter efficiency factor, since converting stored battery energy to AC power always loses some as heat — this matches the exact math from our wattage sizing guide.
Finding Your Device's Actual Wattage
- Check the label or spec plate on the device itself — it's usually printed as "Output: XXW."
- If only amps and voltage are listed, multiply them together (Watts = Volts × Amps).
- Use the running wattage, not the peak or startup wattage listed in some spec sheets.
- When in doubt, round up slightly — a small buffer is safer than an optimistic guess.
For devices with a compressor or motor — fridges, sump pumps, AC units — the number you want is the running wattage, not the brief startup surge. See our running watts vs. surge watts guide for the difference.
What Can Affect Your Real-World Runtime
- Ambient temperature — batteries deliver less usable capacity in cold conditions.
- Battery age and cycle count — capacity gradually declines with use over time.
- Cycling loads — a fridge or AC compressor draws power in bursts, not continuously, so real-world runtime is often longer than a naive calculation.
- AC vs. DC output — charging over USB-C or a 12V port is more efficient than through the AC inverter, so DC-powered devices may run longer than this estimate.
Frequently Asked Questions
How accurate is this runtime calculator?
It gives a solid real-world estimate by accounting for typical inverter efficiency losses (about 15%), but actual runtime still varies with ambient temperature, battery age, and whether your device cycles on and off (like a fridge or AC compressor) rather than drawing power continuously.
Why does the calculator apply an 85% efficiency factor?
Converting stored battery energy to usable AC power always loses some energy as heat in the inverter. Roughly 85% usable output is a realistic, commonly cited figure for modern power stations, so the estimate reflects what you'll actually get rather than the theoretical maximum.
Does this account for a device's startup surge?
No — this calculator estimates total runtime based on continuous running watts, not the momentary startup spike some motors and compressors draw. See our running watts vs surge watts guide if you're checking whether your power station can start a specific device at all.