The cleanest way to size a generator for a CPAP is to start with the CPAP’s real power draw, not just the number printed on the power brick. Look at the label on the machine or power supply for volts and amps, then multiply them to get watts. For example, if the adapter says 24 volts and 2 amps, that is 48 watts at most. In practice, many CPAP machines use less than that most of the time, but sizing from the label gives you a safe starting point.
Next, check whether you use a heated humidifier or heated hose. Those features can change everything. A CPAP without heat might use only 20 to 40 watts, while adding a humidifier can push the load much higher, sometimes into the 60 to 100 watt range or more depending on settings. If you want the generator to last all night, it is smarter to estimate with the humidifier on if you plan to use it. If you normally sleep with the heat turned off, size for that lower number instead.
For generator size, focus on both running watts and inverter quality. A CPAP does not usually need a huge surge to start, but you still want a generator or inverter with some margin. A small pure sine wave inverter or solar generator with at least 2 to 3 times your expected CPAP wattage is a comfortable target. So if your CPAP averages around 40 watts, a unit rated for 150 to 300 watts continuous is plenty from a power perspective, though battery capacity will decide how long it actually runs.
Runtime is the part people often underestimate. Wattage tells you what the machine needs at one moment, but watt-hours tell you how long the power source will last. If your CPAP averages 40 watts and you need 8 hours of sleep, that is about 320 watt-hours, and I would add extra margin for losses, colder weather, or humidifier use. In real-world terms, a 500 watt-hour battery pack is much more comfortable than a 300 watt-hour one for an all-night CPAP setup.
If you are using a fuel generator instead of a battery solar generator, look for one that can run quietly enough for overnight use and keep it outside for safety. Many people actually prefer a battery power station for CPAP because it is silent and easier indoors, especially if the power draw is modest. If your CPAP has a DC adapter option, that can help too, because avoiding AC inverter losses can stretch runtime noticeably.
The most practical approach is to test your exact setup for one night before you rely on it. Measure the CPAP load with your usual settings, then choose a generator or solar battery with extra capacity rather than barely enough. If you want, share your CPAP model and whether you use humidifier heat, and people can help you estimate the size more precisely.
