Peak flow personal best

Your own best reading is what matters, not a chart for someone your height. Add readings from days you felt well and see your lines.

Your details

Reading 1
Reading 2
Reading 3
Reading 4
Reading 5
Age (optional, for a predicted value)
Sex
Height (optional)

Use the highest of your three blows each time.

Best of 5 readings

460 L/min

your working personal best

  • Amber line (80% of best)below 368
  • Red line (50% of best)below 230
  • Your lowest reading420 (91% of best)
  • Predicted for youadd your age (15 to 85) and height to compare your best with the Nunn and Gregg equations

A personal best comes from about two weeks of readings when your asthma is well controlled: blow three times in a row and write down the highest. Ask your GP or asthma nurse to put your own lines on your action plan, as theirs come first.

Call 999 if your reliever is not helping or not lasting 4 hours, you find it hard to walk or talk because you are breathless, or you are wheezing a lot with a very tight chest. Follow your asthma action plan while you wait.

The working

Five good day readings

The highest of 420, 450, 440, 460 and 430 is 460 litres a minute. 80% of 460 is 368, so readings under 368 are amber; 50% is 230, so readings under 230 are red. Your lowest reading, 420, was 91% of your best.

Getting a good reading

Three blows, keep the best

  • Stand or sit up straight and slide the pointer to zero
  • Breathe in as deeply as you can
  • Seal your lips around the mouthpiece and blow as hard and fast as you can
  • Do it three times with a short rest, and write down the highest

Predicted peak flow

What someone your size might blow

Add your age, sex and height and the result also shows the predicted value from the Nunn and Gregg equations (BMJ 1989), the basis of the UK peak flow charts. For a woman of 40 who is 165 cm: e to the power of (0.376 × ln 40 − 0.012 × 40 − 58.8 ÷ 165 + 5.63) = about 483 L/min, so a best of 460 is 95% of predicted. Predicted values are a starting point when you have no best yet; once you know your own best, that is the number your plan uses.

Your plan

Where these numbers go

An asthma action plan has spaces for your best, the number that means you are getting worse, and the number that means an asthma attack. Take these to your GP or asthma nurse to agree yours; if you get a new meter, set a new best.

Read with care

What this cannot tell you

  • Replace your action planYour nurse's numbers come first.
  • Diagnose asthmaThat needs other tests too.
  • Compare metersDifferent meters can read differently.

Questions

Common questions

How do I find my peak flow personal best?

Record your peak flow, morning and evening, for about two weeks while your asthma is under control, and use the highest reading.

What is a good peak flow?

The one that is normal for you. Most action plans set amber below 80% of your best and red below 50%.

Do I need a new best with a new meter?

Yes. Asthma + Lung UK suggests setting a new personal best with your nurse if you change meters.

Sources

Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.

Talk your results through

If a result worries you, book a chat with your GP or practice nurse, or ask a pharmacist. Call NHS 111 if you feel unwell and are not sure what to do, and 999 in an emergency.

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