There is no single normal leak number for every PAP device and mask. Some reports show total flow lost from the system, including intended exhaust flow. Others estimate unintentional leak after accounting for that exhaust. The units may look identical while the quantities differ.
Start with the definition in the exact device report or manual. A limit borrowed from another system may incorrectly label a working mask as faulty—or overlook a problem.
Intended exhaust is not a defect
Many home PAP circuits use a vented mask or connector to clear exhaled gas. The designed flow changes with pressure and the circuit. Other prescribed systems use different exhalation arrangements. Never block an exhaust opening to improve a leak score or substitute a different circuit component without approval.
Unintentional leak can arise at the mask seal, a connection, damaged tubing or the mouth with a nasal interface. The report estimates the amount; it cannot always identify the source.
What the summary figures mean
An average describes the whole recorded period and can hide intermittent episodes. A 95th-percentile value is the level at or below which approximately 95% of the recorded values fall. It is not the worst leak, and it can miss a short but troublesome episode in the remaining tail.
Time above the device's large-leak threshold can be useful if available, but check whether it is shown as minutes or a percentage. A graph adds timing and duration. None of these measures alone tells you whether an episode occurred in REM sleep, unless a separate sleep measurement establishes that.
Match numbers to experience
Leak can cause noise, dryness or air near the eyes. Excessive leak may also affect pressure delivery and event detection. A low AHI during a large leak therefore needs interpretation rather than automatic reassurance.
Conversely, a brief numerical spike without a persistent pattern may not require a new mask. Look for changes after a cushion replacement, connector change or a different sleep position.
Bring the graph, report definition, mask model and symptoms to a review. If a leak is causing discomfort, it deserves attention even when the summary falls below a nominal threshold. The aim is comfortable, effective therapy with an appropriate circuit, not a zero on every display.
Related reading: CPAP leaks: vent flow, mask leaks and mouth leaks