Watts vs. watt-hours: what's the difference?
Watts (W) measure how fast a device uses energy right now. Watt-hours (Wh) measure how much energy is used or stored over time. A power station's watt rating tells you what it can run. Its watt-hour rating tells you for how long.
Almost every confusing moment in choosing a battery comes back to mixing these two up. Once they click, spec sheets start reading like plain language.
The water analogy
Picture a water tank with a tap at the bottom.
- The size of the tank is like watt-hours: the total amount available.
- The flow rate through the tap is like watts: how fast it's being used.
A huge tank with a tiny tap can run a trickle for days but can't fill a bathtub quickly. A small tank with a wide-open tap empties fast. A power station has both a tank (battery capacity, in Wh) and a tap (inverter output, in W), and you need both to be big enough.
The formula connecting them
Hours = watt-hours ÷ watts
A 60 W laptop running for 5 hours uses 300 Wh. A 1,000 Wh battery could, in theory, run that laptop for about 16.7 hours (1,000 ÷ 60). In practice, conversion losses trim that to around 14 hours through an AC outlet. Our runtime calculator handles that adjustment for you.
Examples that make it concrete
| Situation | Watts (rate) | Time | Watt-hours (energy) |
|---|---|---|---|
| LED bulb for an evening | 9 W | 5 h | 45 Wh |
| Microwave reheating a meal | 1,500 W | 3 min (0.05 h) | 75 Wh |
| Laptop for a workday | 60 W | 8 h | 480 Wh |
| Space heater for an hour | 1,500 W | 1 h | 1,500 Wh |
The microwave and space heater both draw 1,500 W, so they need the same size inverter. But three minutes of microwave uses about the same energy as a bulb running all evening, while an hour of space heater would drain a mid-size power station. High watts alone don't make something an energy hog. High watts sustained over time do.
What about kilowatt-hours?
A kilowatt-hour (kWh) is 1,000 watt-hours. It's the unit on your electricity bill. A 2,000 Wh power station holds 2 kWh. That helps put things in perspective: a typical US home uses something like 25–35 kWh on an average day, which is why portable power stations are for essentials, not whole-house backup.
And amp-hours?
Batteries for RVs, boats and DIY systems are often rated in amp-hours (Ah). Amp-hours only describe energy once you know the voltage:
So a 100 Ah battery at 12.8 V (common for LiFePO4) holds about 1,280 Wh, while a 100 Ah battery at 51.2 V holds about 5,120 Wh. Comparing batteries by amp-hours alone can be misleading. Convert to watt-hours first.
How to read a power station spec sheet
- Capacity: 1,024 Wh → the energy stored. Determines runtime.
- AC output: 1,800 W continuous → the most it can power at once without shutting off.
- Surge / peak: 3,600 W → brief bursts for motor startups (see running vs. surge watts).
- Solar input: 600 W max, 12–60 V → the fastest it can charge from panels, and the voltage range panels must stay within.
When someone asks "can this power station run my X?", the answer has two parts. Is X's wattage below the continuous output? And is X's daily energy use comfortably below the capacity? Our power station size calculator checks both at once.