Peak expiratory flow (PEF) is measured in litres per minute. Normal adult peak flow scores range between around 400 and 700 litres per minute, although scores in older women can be lower and still be normal.
Green Zone: 80 to 100 percent of your usual or "normal" peak flow rate signals all clear. A reading in this zone means that your asthma is in good control. Keep using the medicines as directed. Yellow Zone: 50 to 80 percent of your usual or "normal" peak flow rate signals caution.