Watts vs watt-hours

Updated 10 October 2026

Think of a tap and a water tank. Watts (W) are how hard the tap is running right now. Watt-hours (Wh) are how much water has come out over time, and how much is left in the tank.

• Watts tell you whether a power station can run something at all. This is the unit's output rating.
• Watt-hours tell you how long it will run for. This is the battery capacity.

The sum is simple: watts × hours = watt-hours.

Two worked examples

The kettle pulls over thirty times harder than the laptop, but the laptop uses three times as much energy because it runs far longer. A power station needs to cope with both facts: enough output for the kettle, and enough capacity for the laptop.

Why both numbers matter

• A 300 W unit with a huge battery still can't run a 2,000 W kettle. The output is too low.
• A 2,400 W unit with a small battery can boil the kettle but would run flat quickly if you also run a fridge all night.

Why you can't use all of the stated capacity

A power station advertised as 500 Wh won't deliver 500 Wh to your devices. Some energy is lost converting battery power to mains-style power, and not all of the battery is usable. Our power sizer assumes about 85% inverter efficiency and 90% usable capacity, so a 500 Wh unit delivers around 380 Wh to AC devices. These are rough planning figures, and real results vary by unit and conditions. For example, running a 60 W laptop from that unit would give about 6 hours.

Boost modes

Some makers advertise a boost mode (EcoFlow calls its version X-Boost) that lets a unit run some higher-wattage appliances at reduced power. It isn't suitable for every appliance, so check what the maker says it can run before relying on it.