CPAP Mask Sizing: Why Your 'Medium' Isn't Medium

You order a medium because you’re a medium in everything else. It leaks. You tighten it. It still leaks, and now your nose hurts.

Mask sizing is one of the most confusing parts of CPAP therapy, and it’s confusing for a structural reason: there is no standard.

Why sizes don’t transfer

Each manufacturer sizes to its own cushion geometry, and each cushion design has its own shape. A medium nasal cushion in one range and a medium in another are solving different problems with different silicone profiles.

Worse, sizes don’t always transfer within a manufacturer. Someone who wears a medium in one nasal mask may need a small in that same brand’s next model, because the cushion was redesigned.

The practical rule: your size in one mask tells you almost nothing about your size in a different mask. Size every mask from scratch.

Frame size and cushion size are different things

This surprises people. On several popular masks, the frame (the rigid part that holds everything and connects the hose) comes in its own sizes, separate from the cushion.

So you might be a small frame with a medium cushion, and ordering “a medium mask” gets you neither. When you buy a complete mask you’re usually getting a default frame with a chosen cushion size — and when you order replacement cushions later, you order the cushion size only.

If you’ve ever had a mask that seemed almost right but sat oddly high or low, a frame mismatch is a candidate.

Use the sizing template

Every major manufacturer publishes a printable sizing gauge for its masks. This is the single most useful thing you can do, and most people never hear about it.

How to use one properly:

1. Download the specific template for the exact mask model you’re considering — not a generic one.
2. Print at 100% / actual size. Not “fit to page,” which silently rescales it and makes the whole exercise worthless. Most templates include a ruler or a reference square — measure it to confirm your print is accurate before you trust it.
3. Hold it against your face as instructed, in front of a mirror, and read the size.

Two minutes, and it saves the most common ordering mistake.

What the right size looks like

Nasal pillows should seal just at the entrance of your nostrils without being pushed up inside them. If they’re wedged in, they’re too big and will make your nostrils sore. If they slip out, too small.

Nasal masks should sit around the nose — the cushion resting on the bridge and below the nostrils, without covering any part of the mouth and without extending past the sides of the nose. If the cushion sits on the tip of your nose, it’s too small; if it swallows the whole nose area and touches the upper lip, too big.

Full face masks should sit below the lower lip and just under the bridge of the nose, with the cushion clear of the eyes. A common error is going too large, which puts the cushion on the chin and leaks constantly. Manufacturers usually instruct you to measure from just below the nose bridge to just below the lower lip.

Fit it lying down

Your face changes shape when you lie down. Cheeks relax and spread slightly, and the jaw drops back a little. A mask fitted standing at the mirror will often leak the moment you get horizontal.

The correct process: loosen everything, lie down in your normal sleeping position, turn the machine on, then tighten only until the leak stops. More on this in fixing mask leaks.

Fit packs and exchange programmes

Two things worth asking about before you spend money.

Fit packs. Some masks are sold as a pack containing all cushion sizes. If you’re uncertain, this is the cheapest way to get it right, and the spare cushions become replacements later rather than waste.

Mask fit guarantees. Many specialist CPAP retailers let you exchange a mask that doesn’t work within a window of around 30 days, even after use. Terms vary and some exclude certain items, so read them — but buying a mask with no exchange path is how people end up with an expensive drawer.

If you’re getting equipment through insurance, your DME provider may be able to swap you to a different mask, and Medicare builds in a clinical re-evaluation between day 31 and day 91 of therapy¹ — a natural point to say “this doesn’t fit.”

When the size is right and it still doesn’t work

Sometimes the answer isn’t a size, it’s a style. If you’ve sized correctly and still fight leaks, consider whether the mask type suits your face and how you sleep — nasal pillows for beards and side sleeping, full face for mouth breathing, nasal for a middle ground.

That’s the bigger decision, and it’s covered in how to choose a CPAP mask.