TOOL / 01

Estimate the hours first.

Use battery watt-hours, average load, efficiency and a reserve. Change any field to see the planning estimate update instantly.

Estimated runtime10.4 hours

Assumes 85% efficiency and keeps 10% of the battery in reserve.

Planning estimate · not a manufacturer guarantee

Quick answer

Runtime (hours) = battery watt-hours × efficiency × (1 − reserve) ÷ average load in watts. With this calculator's defaults (85% efficiency, 10% reserve), that's hours ≈ Wh × 0.765 ÷ watts. A 1,000 Wh station running a 100 W average load lasts about 7.7 hours. Enter your own numbers above for the estimate, then use the sections below to pick realistic inputs. Most surprises come from the load, not the battery.

Example station: Bluetti AC180. 1,152 Wh battery and 1,800 W AC output, close to the ~1 kWh examples on this page. Enter 1,152 Wh in the calculator to estimate your runtime.

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How to use the runtime calculator

Field What to enter Where to find it
Battery capacity (Wh) Rated capacity in watt-hours Product page, manual or label. If only Ah is given: convert Ah to Wh (Wh = Ah × nominal battery voltage)
Average load (W) Average watts over the time you care about, not the peak Device label (or amps × 120 V), a plug-in watt meter, or the station's output display
Efficiency (%) 85% for AC loads is a reasonable planning default Use the manual's figure if it publishes one. DC/USB paths often lose less
Reserve (%) 10% default, so you're not planning on 0% Raise it if you need charge left for an emergency

Runtime chart: how long will a power station last?

Three portable power stations of different sizes beside a lamp and fan
Hours at common loads with the calculator's default assumptions.

Hours at a steady average AC load, 85% efficiency, 10% reserve:

Capacity 25 W 50 W 100 W 300 W 500 W 1,000 W
256 Wh 7.8 3.9 2.0 0.7 0.4 0.2
500 Wh 15.3 7.7 3.8 1.3 0.8 0.4
1,000 Wh 30.6 15.3 7.7 2.5 1.5 0.8
2,000 Wh 61.2 30.6 15.3 5.1 3.1 1.5
3,000 Wh 91.8 45.9 22.9 7.7 4.6 2.3

These are calculated planning figures, not test results. A load above the station's continuous output rating won't run at all, whatever the battery size.

The formula, step by step

Notepad and portable power station used to estimate runtime by hand
Usable energy, average load, then hours.

Worked example:

  1. Start with a 1,024 Wh battery rating from the station's product sheet.
  2. Use a 75 W average load for a hypothetical laptop-and-router setup.
  3. Keep the default 85% efficiency and 10% reserve.
  4. 1,024 × 0.85 × 0.90 ÷ 75 ≈ 10.4 hours.
  5. Test the real setup: chargers, the station's display and standby draw, and workload all move the average.

For small loads, add the station's own draw

Inverters and screens use power even with a light load. Bluetti's published AC180 runtime formula adds about 15 W of self-consumption to the load, and Jackery lists 18 W standby consumption for the Explorer 1000 v2. Add a similar figure to small loads. In the example above, (75 + 15) W gives about 8.7 hours instead of 10.4. For big loads (500 W+), the overhead barely matters.

Get the average load right

  • Steady loads (lights, routers, fans on one speed): label watts are close to the average.
  • Cycling loads (fridges, freezers, blankets, heaters with thermostats): the label shows the running or maximum watts, but the average is lower because they switch on and off. For fridges, the yellow EnergyGuide or ENERGY STAR kWh/year figure gives an honest average: kWh/yr × 1,000 ÷ 8,760 = average watts. See how many watts a mini fridge uses for a worked example.
  • Motor and compressor starts: a startup surge can trip a station whose continuous rating looks adequate. That's an output problem, not a runtime one. Check it with the wattage calculator.
  • Several devices: add their average watts together.
  • Measure if it matters. A plug-in watt meter or the station's output display, read over a few hours, beats any label.

What shortens runtime

  • AC inverter losses. Use DC or USB-C outputs when the device supports them.
  • Cold batteries. Capacity drops in the cold, and many stations limit charging below freezing.
  • Battery age. LiFePO4 cycle ratings (for example, 4,000 cycles to 80% on some current models) describe slow capacity loss. See battery life.
  • Low-battery cutoff and eco/auto-off modes that shut AC outlets off under light loads
  • Pass-through charging while running loads. See pass-through charging.

Runtime calculator FAQ

How long will a 1000Wh power station last?
About 7.7 hours at a 100 W average load, 15 hours at 50 W, and 2.5 hours at 300 W, assuming 85% efficiency and a 10% reserve. Small loads run a little shorter once you add the station's own standby draw.
How do I calculate power station runtime?
Multiply the rated watt-hours by efficiency (about 0.85 for AC) and by 0.9 for a 10% reserve, then divide by the average load in watts. For example, 1,024 × 0.85 × 0.90 ÷ 75 ≈ 10.4 hours.
Why does my power station run shorter than the calculator says?
Usually the real average load is higher than assumed, the station's own standby draw wasn't counted, the battery is cold or aged, or an eco mode switched the outlet off. Measure the actual load over a few hours and re-run the estimate.
How do I convert mAh or Ah to watt-hours?
Wh = Ah × volts, or mAh × volts ÷ 1,000. Use the battery's nominal voltage, not the USB 5 V output voltage, which overstates capacity. For a step-by-step converter, use the amp hours to watt hours calculator.
Can I use this calculator for a fridge or CPAP?
Yes, as long as you enter the average watts. Fridges cycle, so use kWh/year ÷ 8.76 for average watts. For a CPAP, use measured watts with your humidifier setting. See our CPAP guide and refrigerator guide.
Does a solar generator runtime calculator work the same way?
Yes. A "solar generator" is a power station plus panels. Runtime from the battery uses the same formula. Solar input during the day adds energy back, which you can plan with our solar charging guide.

Sources

Planning guide · United States context · Updated October 24, 2026. Product lines, firmware and manufacturer limits change; verify the current manual before buying or connecting a load.