How this calculator works
The original 1989 Nunn and Gregg equations estimate mean peak expiratory flow for ages 15 to 85 from age, height and sex in the UK study population of healthy lifelong nonsmokers. The male age coefficient is 0.0151 in the original paper, not the frequently rounded 0.015. The instrument used the historical Wright scale; do not compare its prediction directly with a modern EU-scale meter without an appropriate validated correction. No ethnicity correction is applied or implied. Personal-best comparisons require the same meter scale, and daily variability here is a single-day amplitude-to-mean calculation, not a multi-day asthma diagnosis. The result is an estimate for information only and is not medical advice.
Formula
Male ln(PEF in L/min) = 0.544 ln(age) - 0.0151 age - 74.7/height(cm) + 5.48. Female ln(PEF) = 0.376 ln(age) - 0.0120 age - 58.8/height(cm) + 5.63. Percentage of reference = measured/reference x 100. Daily variability = (maximum - minimum)/[(maximum + minimum)/2] x 100.
Worked example
For a 40-year-old male at 175 cm, the original equation gives 636.44199 L/min. A measured 500 L/min is 78.56% of predicted and 83.33% of a 600 L/min personal best. Daily readings of 550 and 450 L/min have amplitude-to-mean variability 20%.
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Frequently asked questions
Which meter scale does the prediction use?
It uses the original historical Wright scale. Modern EU-scale readings can differ, so verify the scale before comparing measured flow with this prediction.
Is this a personal asthma action plan?
No. Use the plan and personal-best reference agreed with the treating professional. The calculator does not assign treatment zones.
Can this apply a race or ethnicity correction?
No. It provides the cited UK study equation only. Do not assume it is validated for every population or use an invented correction.