Using the nasal cushion sizing gauge (included with the mask or download at the link above), hold it horizontally under the nose. Select the cushion size based on where the outer edge of the nostrils and tip of the nose contact the gauge.
Note: Four cushion sizes (small, medium, large, medium-wide) are available. Please refer to your instructions for use for further fitting information.
Philips always recommends consulting a sleep or respiratory therapist in fitting a mask to ensure a proper sizing and fit.