Peak expiratory flow rate (PEFR) is the maximal expiratory flow rate sustained by a subject for at least 10 milliseconds expressed in Litre per minute (L/min). PEFR is a simple, reliable, reproducible and easily measurable ventilatory lung function test. This simple test had been measured by various types and shapes of instruments for long since, now miniWright peak flow meter is widely used to measure the of PEFR values. Mini-Wright peak flow meter is cheap, easily portable and reproducible device for PEFR even below the age 5 years. Different countries use their own nomogram or prediction equation to find out mean PEFR values of particular height. Similarly, the prediction equation for calculation of PEFR values of Bangladeshi boys and girls are 5.96XHeight-495 and 5.70XHeight-479 respectively. Peak expiratory flow rate is very useful tool for diagnosis, management and follow up of reversible airway diseases.