There is no point reaching for a calculator that cannot show its working. This one starts from pef maximum, pef minimum, age, ethnicity, height, measured peak flow, personal best, sex and one way and reports estimated peak flow, diurnal variability and % of estimated pef, so you can see how each answer follows from the numbers you entered.
What Is the Peak Flow Calculator?
The peak flow calculator gives you an estimate of estimated peak flow, diurnal variability and % of estimated pef based on pef maximum, pef minimum, age, ethnicity, height, measured peak flow, personal best, sex and one way.
It is a quick reference figure rather than a diagnosis, and it is most useful for tracking how a number moves over time rather than for interpreting a single reading.
How the Peak Flow Estimate Is Worked Out
The calculation follows published reference relationships, so it is a reasonable approximation when the inputs are accurate. It assumes an average adult and does not account for individual variation.
If you are comparing two people, or the same person over a period of weeks, keep the method and the inputs identical. A change in the method can easily look like a change in the person.
What This Calculator Does Not Do
It does not diagnose anything, and it does not replace advice from a clinician. If a figure comes out at an extreme, or if it differs sharply from what you expect, that is a reason to speak to a professional rather than to adjust the inputs.
Nothing you type here is stored or sent anywhere. The whole calculation happens in your browser.
A Worked Example
Working through an example, with pef maximum set to 10, pef minimum set to 5, age set to 2, the calculator returns estimated peak flow of 1.67, and % of estimated pef of 600, and diurnal variability of 50. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out estimated peak flow?
Enter pef maximum, pef minimum, age, ethnicity, height, measured peak flow, personal best, sex and one way. The calculator then works through the relationship and reports estimated peak flow, diurnal variability and % of estimated pef.
What does the peak flow actually calculate?
It takes pef maximum, pef minimum, age, ethnicity, height, measured peak flow, personal best, sex and one way and converts them into estimated peak flow, diurnal variability and % of estimated pef using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter pef maximum?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Do I have to fill in every field?
Only the fields a particular result depends on. If you leave one blank, the results that need it simply show a note instead of a number, and everything else still works.
Can I use this for a quick estimate as well as a precise answer?
Yes. The calculator is built for quick checks, so round your inputs to a sensible number of significant figures and the result will be just as useful. If you need more precision, keep the same method and add digits to the inputs rather than adjusting the method itself.