Quick answer: Enter your power station's battery capacity in watt-hours and your devices' watts, quantities and duty cycles, and this calculator estimates runtime, or reverses the calculation to find the battery size you need. With the defaults, a 1,024 Wh station running a 122 W load gives about 5 hours 47 minutes. It is free, with no signup, and you can also try the Propane Tank Runtime Calculator and 3D Printing Cost Calculator.

Power Station Runtime Calculator | Tools Bag

Tools Bag · Power Planning

Portable Power Station Runtime Calculator

Find out how long a power station can run your devices, or estimate the battery capacity you need for a target runtime. Add multiple appliances and account for efficiency and reserve.

Power station

Enter the rated battery capacity in watt-hours (Wh).

Battery capacity (Wh)

Target runtime (hours)

Devices

Use a measured wattage when available. Duty cycle estimates the average time a cycling device is actually drawing its listed power.

Planning assumptions

Inverter efficiency (%)

Usable battery capacity (%)

Reserve (%)

Power station continuous output (W)

Optional surge rating (W)

These are planning assumptions, not universal specifications. Check your power station manual for its actual usable capacity, output limits and efficiency.

ESTIMATED RUNTIME

—

Add a device to calculate.

—Average load

—Usable delivered energy

—Capacity used

How this works

The calculator first estimates the average electrical load from every device. For a cycling appliance, its wattage is multiplied by its duty cycle. The battery's rated Wh is then adjusted for the usable battery percentage, inverter efficiency and reserve.

Average load = Σ (watts × quantity × duty cycle)
Delivered energy = battery Wh × usable % × efficiency × (1 − reserve)
Runtime = delivered energy ÷ average load

In battery-size mode, the same relationship is reversed: the tool works out the energy required for your target runtime and adds the selected planning allowances.

Example: a 1,024 Wh station with 90% usable capacity, 85% efficiency and 10% reserve does not deliver the full 1,024 Wh to AC devices. Real results vary by model and operating conditions.

Tips

Check the nameplateUse the appliance's rated watts, or measure actual consumption when possible.

Watch startup loadsFridges, pumps and compressors may briefly require much more power than their running wattage.

Don't confuse W and WhWatts describe power draw; watt-hours describe stored or consumed energy.

Keep a reserveA reserve helps avoid planning around the absolute battery limit.

AC and DC differUsing a DC output can avoid some inverter losses, depending on the equipment.

Test critical loadsFor medical equipment or essential refrigeration, verify real-world runtime with the actual setup.

How this calculator works

The calculator works in three steps. First it adds up the average load of everything you plan to run. For each device, average load is watts times quantity times duty cycle, so a fridge that cycles half the time counts at half its rated watts. Then it works out how much energy the station can actually deliver, because the rated watt-hours are reduced by usable capacity, inverter efficiency, and the reserve you keep back. Finally it divides delivered energy by average load to get runtime.

Average load = sum of (watts x quantity x duty cycle). Delivered energy = battery Wh x usable % x efficiency x (1 - reserve). Runtime = delivered energy divided by average load. In battery-size mode the same relationship is run in reverse: the tool works out the energy needed for your target runtime and adds the planning allowances back in.

Worked example: the default setup

Use the defaults: a 1,024 Wh station, a Wi-Fi router at 12 W, a laptop at 60 W, and a fan at 50 W, each with quantity 1 and duty cycle 100%, with 90% usable capacity, 85% inverter efficiency, and a 10% reserve.

Average load = 12 + 60 + 50 = 122 W.
Delivered energy = 1,024 x 0.90 x 0.85 x 0.90 = 705 Wh (705.024 Wh before rounding).
Runtime = 705 divided by 122 = 5.78 hours, which the tool shows as 5h 47m.
Capacity used = 705 divided by 1,024 = 69%.

So the same station does not deliver the full 1,024 Wh to AC devices: about 319 Wh is taken by the usable-capacity, efficiency, and reserve allowances. Also check the result against the station's continuous output and any surge rating, because a load above those limits is a problem even if the runtime looks fine.

Quick reference: runtime at the default settings

The table below keeps the default delivered energy of 705 Wh and only changes the average load, so it shows why halving the load roughly doubles the runtime.

Average load	Estimated runtime
50 W	About 14.1 hours
100 W	About 7 hours 3 minutes
200 W	About 3 hours 32 minutes
500 W	About 1 hour 25 minutes

These are planning estimates. Real runtime varies with battery age, temperature, startup loads, and the actual efficiency of your station, so test critical loads with the real setup.

FAQ

How long will a 1,000 Wh power station run a 100 W device?

Under the default planning assumptions used here, the estimate is about 6.9 hours. Change the efficiency, usable capacity and reserve to match your specific station.

What size power station do I need for a refrigerator?

It depends on the refrigerator's average energy use and startup requirement. Enter its running watts, estimate its duty cycle, and check the station's continuous and surge ratings.

Why is my real runtime different from the calculator?

Battery age, temperature, inverter losses, device cycling, startup loads, output-port limits and the manufacturer's battery-management system can all change the result.