PEF Calculator

PEF Calculator – Peak Expiratory Flow

PEF, or Peak Expiratory Flow, measures how fast you can blow air out of your lungs during a forceful exhalation. It is particularly used in monitoring asthma and other lung diseases – a PEF meter is an inexpensive, portable device that allows self-monitoring at home without special equipment.

What is the PEF value used for?

Regular monitoring of the PEF value helps detect bronchial constriction before symptoms become clearly noticeable – this allows for timely responses, such as enhancing medication. For those with asthma, a PEF diary is a common and useful tool that helps both the patient and the treating physician see how the disease behaves in daily life and how effective the treatment is.

How is the expected value calculated?

The normal expected value of PEF primarily depends on height, age, and gender – taller individuals statistically have larger lungs and thus a higher expected PEF value, while aging decreases the expected value as lung elasticity gradually declines. The calculator uses a generally accepted approximation based on these factors.

Your personal best value is more important than the population expected value

While the population-level expected value is a useful starting point, the most important aspect of asthma self-monitoring is to track your own personal best value – the PEF reading you achieve when your breathing is in the best possible balance. Treatment plans (e.g., “green-yellow-red” zone system) are generally based on a percentage of your personal best value, not the population average expected value.

How to perform a PEF measurement correctly?

• Stand or sit with your back straight before the measurement.
• Breathe in as deeply as you can first.
• Seal your lips tightly around the mouthpiece of the meter.
• Blow out as quickly and forcefully as possible – it’s about speed, not duration.
• Repeat the measurement 2-3 times and record the best result.

This is a statistical expected value, not a diagnostic tool. PEF measurements and their interpretation should always be done in conjunction with a doctor or nurse, using a calibrated PEF meter.