Predicted Peak Flow (PEF) Calculator

About this calculator

Peak expiratory flow (PEF) is the fastest speed of air a person can force out of their lungs after a full breath in, measured in litres per minute with a handheld peak flow meter. Because healthy lung capacity varies predictably with age, height, and sex, standard reference formulas — such as those from Nunn & Gregg — provide a predicted PEF value that a person's own measured reading can be compared against, expressed either directly or as a percentage of predicted.

This informational reference is widely used by people managing asthma or COPD, and by clinicians monitoring respiratory function, since a reading that drops well below the predicted value can be a signal worth discussing with a healthcare provider. The calculator provides the general predicted figure for educational purposes only — it doesn't diagnose or interpret an individual's results, which should be reviewed with a doctor.