Watts vs. watt-hours: how to size a portable power station

One number describes power; the other describes energy

A device drawing 60 W for four hours uses 240 Wh: 60 × 4 = 240. Two devices drawing 60 W and 40 W at the same time need 100 W of continuous output. Run them together for four hours and they use 400 Wh at the devices.

A 1,000 W inverter is not a 1,000 Wh battery. Stations with the same output rating can have very different capacities. Increasing the output rating alone does not increase the energy stored.

Worked example: laptop plus internet

Assume a laptop averaging 60 W and an internet device averaging 40 W for eight hours. The energy budget is (60 × 8) + (40 × 8) = 800 Wh. With 80% usable battery energy, nominal capacity calculates to 800 ÷ 0.8 = 1,000 Wh. The continuous-load requirement remains 100 W before any separate startup or port checks.

If the laptop runs for eight hours but internet is needed for only four, the budget changes to 640 Wh and the calculated nominal minimum becomes 800 Wh. Set the runtime for each device separately in the calculator; the durations do not have to match.

What could a 1,024 Wh battery run?

Using the site’s 80% assumption gives 819.2 Wh of estimated usable energy. Divide by the load. The examples assume a fully charged battery, steady consumption and no recharge, and do not account individually for each inverter’s overhead or shutdown behavior.

Check ports, surge and voltage as separate limits

The AC output rating does not describe every USB-C port. A laptop may require a particular USB Power Delivery profile, and sharing ports can reduce the available output. Motors and compressors may need startup power above their running power. Check the exact documentation rather than multiplying by a universal surge factor.

For U.S. products, verify the outlet and appliance voltage. A capacity comparison cannot make a 120 V appliance compatible with a different-voltage output. This catalog focuses on U.S. variants; the Spanish translation does not change their electrical specifications.

Use measured draw when the load changes

A charger’s maximum rating is not necessarily the device’s average use. For a variable load, record energy and time during a representative session: 300 Wh over five hours gives 60 W average. Add a practical reserve if the next session could be heavier.

For a refrigerator that cycles on and off, use energy over a representative period and check compressor startup separately. For Starlink, identify the hardware version. Follow the related guides below for those two cases.