Wh vs W: Watts, Watt-Hours & Battery Runtime
Watts (W) measure the power a station can deliver at once; watt-hours (Wh) measure energy available over time. W tells you whether an appliance's input fits within the station's output, while Wh helps estimate how long it can run.
Compare the combined running watts of the appliances you plan to use with the station's continuous output, then estimate runtime as AC-delivered Wh ÷ combined average load W. Startup demand is a separate surge check.
Watt-hours: the size of the tank
A watt-hour is one watt of power used for one hour. It measures a quantity of energy. The rated Wh describes battery-side energy; AC-delivered Wh is the more useful figure for estimating an AC load’s runtime.
Think of it like a fuel tank: the same amount of energy can support a higher power draw for less time or a lower draw for more time. In an ideal calculation, 1,000 Wh corresponds to 1,000 W for one hour, 100 W for ten hours, or 10 W for one hundred hours. A real station delivers less energy at its outlets after conversion losses, and chemistry and pack design affect size and cost.
The catch: rated battery capacity is not a measurement of energy delivered at the AC outlet. Conversion losses, the station’s protection settings and the load affect that result. Our model pages distinguish battery-side energy from AC-delivered watt-hours, and label the outlet figure as measured or estimated.
Watts: the size of the tap
A watt is a rate — power flowing right now. The continuous watts rating describes the AC load the inverter can sustain; the separate surge rating covers supported brief startup demand. These ratings decide what you can plug in, not how long the battery lasts.
If the tank is watt-hours, watts are how wide you can open the tap. Compare one appliance’s input, or the combined input of appliances running together, with the station’s sourced continuous output rating. A full battery cannot make the inverter supply more continuous power than that rating allows.
Stored energy alone does not establish appliance compatibility. The continuous output rating is a separate check against the load you plan to run.
The two numbers, side by side
Watts answer “can I run it?” Watt-hours answer “for how long?” A complete sizing decision needs both, plus the surge rating for anything with a motor.
| Watts (W) | Watt-hours (Wh) | |
|---|---|---|
| What it is | A rate — power flowing now | A quantity — energy stored |
| Analogy | Width of the tap | Size of the tank |
| Set by | The inverter | The battery cells |
| Answers | Can I plug this in? | How long will it run? |
| If it's too small | The device won't start (trips) | It starts, but dies early |
First check that the station’s continuous output can cover the devices you will run together. Then divide AC-delivered energy by their combined average draw to estimate runtime. For a fridge, average draw accounts for compressor cycling; startup power is a separate output check.
How to convert watts and watt-hours
You cannot convert watts to watt-hours without a duration. Energy (Wh) = power (W) × time (hours). Rearrange it to get average power = Wh ÷ hours, or runtime = delivered Wh ÷ average W.
For household AC appliances, start with our AC-delivered capacity reading so conversion losses are counted once. For a USB or DC connection, use the appropriate output path in the calculator. If your question started as milliamp-hours, our mAh-to-Wh guide explains why the pack voltage must be stated before any conversion is meaningful. Our power-station sizing tool combines the energy and output checks; the CPAP and fridge runtime calculators let you enter your own load.
Don't forget surge watts
Motors and compressors can draw more power at startup than while running. Check the station’s sourced surge rating and supported duration as well as continuous output; startup compatibility cannot be inferred from running watts alone.
Read the appliance’s manual or energy label instead of assuming a universal startup multiplier. Resistive heaters mainly demand sustained output, while compressors and motors also need startup headroom. Our sizing tool checks the worst single-start moment against each station’s sourced surge spec, and flags any station whose surge rating we can’t verify rather than guessing.
Frequently asked questions
- What is the difference between Wh and W on a power station?
- Watt-hours (Wh) measure energy stored; watts (W) measure power the station can deliver at a time. Compare an appliance's input watts with the station's sourced continuous output, and check startup demand against its surge rating. Estimate runtime by dividing AC-delivered Wh by the appliance's average watts.
- How do I calculate how long a power station will run my device?
- For an AC appliance, divide AC-delivered watt-hours by its average power draw in watts. If you start with battery-side usable energy instead, multiply by AC efficiency first. Do not apply conversion losses again to an AC-delivered figure. Our model pages label delivered capacity as measured or estimated, and our sizing tools account for the output path.
- How many watt-hours do I need?
- Multiply each device's average watts by the hours you need it, then add those watt-hours together. Compare that demand with AC-delivered capacity for household AC loads, rather than treating rated battery capacity as outlet energy. Use your own CPAP settings or fridge energy label in our runtime calculators; those loads vary with settings and duty cycle.
- Why can't I run my microwave even though the battery is full?
- A full battery cannot compensate for insufficient inverter output. Check the microwave's electrical input on its label or manual, rather than its advertised cooking power, against the station's continuous and startup limits. Also include any other appliances running at the same time.
- What are surge or starting watts?
- Motors and compressors can briefly draw more power at startup than during normal operation. Check the appliance's starting-power requirement against the station's sourced surge rating and supported duration. A running-watts match alone does not establish that the appliance will start.