Reading your sleep data
How to Read Your CPAP Data: AHI, Leak, Usage and Events
Your CPAP records four main things: how long you used it, how many breathing events per hour still happen (AHI), how much air leaks from the mask, and what pressure it delivered. Use those numbers to spot mask or habit problems, and bring trends, not single nights, to your clinician.
Usage hours
Usage is the time the machine detected you breathing through the mask. Insurers care about it: Medicare's rule is 4 hours or more on 70% of nights in a 30 day stretch in the first 3 months.
The DreamStation 2 shows the number of 4+ hour nights in the last 30 days with a goal of 21, and ResMed's myAir gives 10 points per hour of use up to 70.
AHI: events per hour
AHI is the apnea hypopnea index: the average number of apneas (breathing stops) and hypopneas (shallow breathing) per hour of use. On a diagnostic test, an AHI under 5 is considered normal, 5 to under 15 mild, 15 to under 30 moderate, and 30 or more severe, categories set by an AASM task force in 1999.
The machine's AHI is an estimate based on airflow, not a full sleep study. A single high night after alcohol or a cold matters less than a rising trend.
Leak
Every CPAP mask has a built in vent that leaks on purpose. The machine reports unintentional leak beyond that. High leak lowers the pressure that reaches your airway and can make the event count less reliable.
Philips describes mask fit as a measure based on leak, and ResMed's myAir mask seal score falls as leak increases. Leak spikes that start when you roll over point to fit or pillow problems; leak all night may mean wrong size, worn cushion or mouth breathing with a nasal mask.
Pressure
On fixed CPAP the pressure is flat. On auto CPAP you will see it rise and fall within your prescribed range, often with a median and a 95th percentile value.
If your auto machine spends most of the night at its maximum, or your AHI stays high, that is a reason to talk to your clinician. Pressure changes should only be made by your prescriber.
Event types
Detailed reports separate obstructive apneas, central or clear airway apneas, hypopneas and sometimes RERAs (respiratory effort related arousals) or flow limitation. ResMed says the AirSense 11's event detection identifies central sleep apnea, RERAs and Cheyne Stokes respiration.
A pattern of many central events is something to raise with your clinician; see our guide on central vs obstructive events.
Supplies that can help
A soft strap that supports the jaw to help keep the mouth closed, used mainly with nasal and nasal pillow masks to reduce mouth leaks.
Soft fabric liners that sit between your skin and the mask cushion to reduce skin irritation, red marks and the noisy leaks some people get from …
A pillow with cutouts or a contoured edge so a mask and hose are not pushed out of place when you sleep on your side.
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Frequently asked questions
What numbers should I look at on my CPAP?
Start with hours used, AHI and leak. Those three explain most problems. Pressure and event types are useful details to bring to your clinician.
Why is my CPAP AHI different from my sleep study?
Your sleep study measured untreated breathing with more sensors. The CPAP number is a treated, machine estimated AHI, so it should be much lower.
What does a high leak on my CPAP mean?
Air is escaping around the mask or out your mouth beyond the mask's designed vent. Refit or resize the mask, replace a worn cushion, or address mouth breathing.
Can I see my CPAP data without an app?
Yes. Many machines show a sleep report on screen, and the SD card can be read with free software like OSCAR.
Sources
Last reviewed October 11, 2026. How we research · Report an error