Watts vs Watt-Hours: What Power Station Buyers Need to Know

Watts (W): a rate of power, not an amount

A watt measures how much power something draws or delivers at a given instant — it's a rate, the same way miles per hour is a rate of speed. A 100 W device pulls 100 watts whether it runs for one minute or ten hours; the watt figure itself doesn't change with time.

On a power station, the watts figure appears as a continuous output rating (how much it can deliver steadily) and a surge or peak rating (how much it can deliver briefly, for motor startups).

Watt-hours (Wh): an amount of energy over time

A watt-hour is energy — watts multiplied by the hours they're sustained. A 100 W device running for 3 hours uses 300 Wh, regardless of how that power was delivered moment to moment.

A power station's battery capacity is rated in watt-hours (or often kilowatt-hours, kWh — 1,000 Wh). That number tells you how much total energy is stored, which determines how long it can run something once that something is actually running.

Why mixing them up leads to the wrong purchase

A device's watts tells you whether a station can start and run it at all — check that against the station's continuous and surge output. A device's watt-hours (watts × hours of use) tells you how long the station's capacity will sustain it — check that against the battery's usable Wh.

Buying based on only one of the two numbers is the classic mistake: a station with plenty of watt-hours but too low a watt rating can fail to start a device entirely, while a station with a high watt rating but modest watt-hours can start anything but run out quickly.

Converting between the two

Watt-hours = watts × hours of use. If you only know amps and volts (common on rating labels), watts ≈ amps × volts, and you can convert from there.

Working the other direction: hours of runtime ≈ usable battery Wh ÷ device watts. PowerMatchLab uses roughly 85% of nameplate capacity as usable energy in its own runtime and sizing calculations, to account for inverter and conversion losses.

Typical wattage ranges for common devices

These are broad, commonly cited category ranges, not a measurement of any specific product — always check your own device's rating label or manual for its real figure.

• Phone or small USB device charging: roughly 5-20 W
• Laptop: roughly 30-100 W
• LED TV: roughly 30-150 W depending on size
• Box fan or CPAP machine without a heated humidifier: roughly 30-60 W
• Full-size refrigerator (average, cycling): roughly 100-200 W average, with a startup surge several times higher
• Microwave or coffee maker: roughly 600-1,200 W
• Space heater or hair dryer: roughly 750-1,800 W

Continuous watts vs. surge watts

Continuous watts is what a device draws while running steadily. Surge (or peak/startup) watts is a brief spike, common in anything with an electric motor — a compressor, a pump, a power tool — often two to three times the running watts for a fraction of a second.

A power station's surge rating needs to clear a device's startup spike, not just its running watts, or the device may fail to start even though the continuous rating looked sufficient.

Applying watts and watt-hours to four common scenarios

The same two questions — can it start and run this (watts), and for how long (watt-hours) — apply differently depending on what you're powering. These four scenarios cover most of what people search for when sizing a station.

• Refrigerator backup: a full-size fridge averages roughly 100-200 running watts but cycles on and off, so its real daily energy use is closer to 1,000-2,000 Wh/day than a simple watts × 24 calculation — and its compressor's startup surge (several times the running watts) is what most stations actually fail to clear. See the refrigerator backup guide and shortlist linked below for the fridge-specific numbers.
• CPAP overnight: most CPAP machines without a heated humidifier draw roughly 30-60 continuous watts, so an 8-hour night is commonly only 240-480 Wh — watts matters less here than confirming a pure sine wave inverter, which most CPAP manufacturers require.
• RV and camping: total watt-hours needed depends entirely on your device list and trip length, not the RV itself — add up every device's watts × hours/day for the trip, then check the single largest surge (often a compressor fridge or an A/C unit) against the station's surge rating.
• Whole-home backup: this is a watts question first — you're choosing which circuits to run (not everything at once), checking each one's running and surge watts against the station or inverter's output, then sizing watt-hours for how many hours of outage you want covered.