Your peak flow depends on your age, height, and sex. As a rough guide, a healthy adult male in his 40s who is 5’10” can expect a predicted peak flow around 596 L/min, while a healthy adult female of the same age at 5’5″ would be closer to 436 L/min. But those population averages are just a starting point. The number that matters most for day-to-day health is your personal best, which you establish by tracking your own readings over two to three weeks when you’re feeling well.
Predicted Peak Flow by Age, Height, and Sex
Peak flow is the fastest rate at which you can push air out of your lungs in one sharp breath, measured in liters per minute (L/min). Predicted values come from large population studies and give you a ballpark for what’s typical among people who share your basic physical characteristics. Three factors drive the number: your height (taller people have larger lungs), your age (peak flow declines steadily after about age 20 in men and 40 in women), and your biological sex (males generally produce higher readings than females).
The table below, based on reference values from the National Heart, Lung, and Blood Institute, shows predicted averages for healthy adults who have never smoked.
Males (by Height and Age)
- Age 20: 554 L/min at 5’0″, 649 L/min at 5’10”, 740 L/min at 6’8″
- Age 40: 509 L/min at 5’0″, 596 L/min at 5’10”, 680 L/min at 6’8″
- Age 60: 463 L/min at 5’0″, 542 L/min at 5’10”, 618 L/min at 6’8″
Females (by Height and Age)
- Age 20: 390 L/min at 4’7″, 460 L/min at 5’5″, 529 L/min at 6’3″
- Age 40: 370 L/min at 4’7″, 436 L/min at 5’5″, 502 L/min at 6’3″
- Age 60: 350 L/min at 4’7″, 412 L/min at 5’5″, 475 L/min at 6’3″
These numbers represent averages, not hard cutoffs. Body weight, fitness level, and smoking status also play a role. Smoking is consistently linked to lower peak flow, even in people who haven’t been diagnosed with a lung condition.
Why Your Personal Best Matters More
Predicted values are useful for a first comparison, but international asthma guidelines recommend using your own personal best as the benchmark for ongoing monitoring. The reason is straightforward: population averages can be significantly off for any given individual. In one study of 166 people with chronic asthma, 43% had a personal best that was more than 10% higher than their predicted value, and 12% had a personal best more than 10% lower. When doctors relied on the predicted number instead of the personal best, they either overestimated or underestimated actual lung function in more than half of patients.
To find your personal best, use your peak flow meter at the same time each day for two to three weeks during a period when your breathing feels good and is well controlled. Take three readings each time and record the highest one. The highest number you achieve across that entire period becomes your personal best. You can then use it as the reference point for tracking changes.
The Traffic Light System
Once you know your personal best, the simplest way to interpret daily readings is the three-zone system, color-coded like a traffic light.
- Green zone (80% to 100% of personal best): Your airways are open and your breathing is well controlled. No changes to your routine are needed.
- Yellow zone (50% to 80% of personal best): Your airways are narrowing. This is a signal to follow whatever action plan you’ve set up with your healthcare provider, which typically involves adjusting medication.
- Red zone (below 50% of personal best): This is a medical alert. Your airways are significantly restricted, and you need immediate treatment.
To put that in concrete terms: if your personal best is 500 L/min, a reading of 400 or above means you’re in the green zone. A reading between 250 and 400 puts you in the yellow zone. Anything below 250 is the red zone.
Peak Flow in Children
For children, height is the strongest predictor of peak flow because kids of the same age can vary dramatically in size. A large study of children aged 5 to 14 found that readings roughly follow a simple pattern: for every additional 10 centimeters of height, peak flow increases by about 40 to 45 L/min.
Some representative averages for children by height:
- 110–119 cm (about 3’7″ to 3’11”): ~200–210 L/min
- 130–139 cm (about 4’3″ to 4’7″): ~280–295 L/min
- 150–159 cm (about 4’11” to 5’3″): ~365–375 L/min
- 170 cm and above (5’7″+): ~420–460 L/min
Boys tend to have slightly higher readings than girls at most heights, though the gap is small until puberty, when it widens noticeably.
Peak Flow for Asthma vs. COPD
Peak flow monitoring is a standard part of asthma management. Because asthma involves reversible airway narrowing, peak flow numbers shift meaningfully in response to triggers, flare-ups, and treatment, making daily tracking genuinely useful.
For COPD, the picture is less clear. The airway obstruction in COPD is largely fixed rather than reversible, so daily peak flow readings tend to vary less and provide less actionable information. Most COPD management relies on spirometry testing done in a clinic rather than home peak flow meters. If you have COPD and are wondering whether to track peak flow, it’s worth discussing with your provider whether it would add anything beyond your existing monitoring.
Getting an Accurate Reading
A peak flow meter is only useful if you’re using it correctly, and errors are surprisingly common. Research observing patients during the maneuver found mistakes at nearly every step. The most frequent problems include not taking a full breath in before blowing, not giving maximum effort on the exhale, and stopping after one attempt instead of doing three.
For a reliable reading, stand up straight, take the deepest breath you can, seal your lips tightly around the mouthpiece, and blow out as hard and fast as possible in a single short burst. Think of it as blowing out birthday candles with maximum force, not a long slow exhale. Do this three times and record the highest of the three. One study even found patients accidentally pushing the meter’s indicator with their tongue or cheek muscles, which inflates the number. Keep your tongue below the mouthpiece opening and let your lungs do the work.
Consistency matters too. Use the same meter each time (different brands can give slightly different readings), and measure at the same time of day. Peak flow naturally dips in the early morning and rises in the afternoon, so comparing a 6 a.m. reading to a 3 p.m. reading from the day before can be misleading.