Peak Flow Chart

How to use this peak flow chart

1. Enter your age, height, and sex. That's enough to produce your predicted peak flow — the average for someone your size without lung disease. Height can be entered in centimetres or inches; the conversion runs automatically. For children under 15 the prediction is set by height alone, so the sex buttons dim out.
2. Add your personal best if you know it. This is the single most important box on the page. Your zones should be calculated from your best number, not from a population average, and entering it switches every band below to your real figures.
3. Don't have a personal best yet? Leave it blank. The tool falls back to the predicted value and labels it honestly, so you can see your approximate zones today and replace them properly in two weeks.
4. Enter today's reading. Blow three times and enter the highest of the three, never the average. You'll get your percentage and your zone, with what that zone actually calls for.
5. Read your zones in L/min. The three bands below the result convert the 80% and 50% thresholds into the real numbers you'll be comparing against on the meter.
6. Download the 4-week diary. It prints with your green, yellow, and red boundaries already filled in, plus any readings you've logged. Take it to your next appointment.

Why this peak flow chart is different

Search for a peak flow chart and you get two kinds of page, neither of which finishes the job. The patient-education articles explain the traffic-light zones beautifully and then decline to give you a number, telling you to ask your provider. The one real calculator is built for clinicians, gates its result behind a race input, and returns a bare figure with no zones, no chart, and no way to record anything. Here's what this page does instead:

• Prediction and zones in one place. You get the predicted number and the green/yellow/red boundaries in L/min, from the same inputs. Everywhere else you get one or the other and do the arithmetic yourself.
• Personal best comes first. Clinical guidance is unambiguous that zones belong to your own best reading, not to a population average — so this tool treats the personal-best box as the primary input and says clearly, on the result, which of the two it used.
• The chart is a real table, not a JPEG. Normal values by age and height are rendered as live text you can read on a phone, copy, and have read aloud by a screen reader — with your own row and column highlighted as you type. Most "peak flow charts" online are scanned images of a nomogram.
• The printable comes with your zones already on it. Every peak flow diary in circulation is a blank grid that expects you to work out 80% and 50% of your best by hand and pencil the lines in. That step is exactly what gets skipped. Ours prints them for you.
• It tells you which reference standard the number came from. Predicted peak flow varies a lot between reference sets, and comparing a reading from one scale against a prediction from another is a genuine way to frighten yourself for no reason. This page states which equations it uses and why, in plain language.
• No race input, no login, no ads, no email gate — and a named physician's byline rather than an anonymous chart list.

How this peak flow chart works (the equations)

Peak expiratory flow (PEF) is the fastest speed you can blow air out, measured in litres per minute. A predicted value estimates what someone of your age, height, and sex would typically manage without lung disease. This tool uses the regression equations that sit behind the peak flow nomograms distributed by asthma organisations and printed on EU-scale meters:

• Adults, aged 15 and over (Nunn & Gregg, 1989), with height in metres:
  Men: PEF = [(height × 5.48) + 1.58 − (age × 0.041)] × 60
Women: PEF = [(height × 3.72) + 2.24 − (age × 0.03)] × 60
• Children, aged 5 to 14 (Godfrey et al., 1970), with height in centimetres:
  PEF = [(height − 100) × 5] + 100
  Note that sex isn't in the children's equation at all — height carries essentially all of the signal before puberty.

The zones are the American Lung Association traffic-light system, applied to your baseline: green is 80% of baseline and above, yellow is 50–79%, and red is anything under 50%. If your personal best is 400 L/min, that puts your green zone at 320 and above, yellow between 200 and 319, and red below 200.

The part nobody mentions: which reference standard your number came from

There is more than one published set of normal values, and they do not agree. The equations above are the EU / EN 13826 scale — the standard used by the Mini-Wright-style meters most people are handed and by the charts asthma charities publish. The United States also has the NHANES III reference set from the CDC, which is what clinician-facing calculators typically run, and it returns substantially higher numbers: for a 40-year-old woman of 175 cm, roughly 595 L/min against 453 L/min from the equations above.

That gap matters. If you blow into an EU-scale home meter and compare the result against an NHANES III prediction, you will look obstructed when you are not. It is one more reason the number that actually governs your care is your own personal best, measured on your own meter — the reference equations are a starting point for people who don't have one yet, nothing more.

Limitations, honestly. Predicted peak flow carries wide natural variation: two healthy people matched for age, height, and sex can differ by 20% or more, which is why peak flow is not used to diagnose asthma. Readings also vary through the day, typically lowest in the early morning. And a meter that has collected dust or mucus reads low — clean yours per the instructions and use the same one every time.

Three worked examples

A 40-year-old woman, 165 cm, no personal best yet

Her predicted peak flow comes out at 431 L/min. Without a personal best, the tool uses that as her baseline and shows a provisional green zone of 345 and above, yellow from 216 to 344, and red below 216. The right next step is two weeks of twice-daily readings while she feels well — the highest number from that fortnight becomes her real personal best, and the zones get recalculated around it. Recording those two weeks is exactly what the printable diary is for.

A 40-year-old man, 175 cm, personal best 520

His predicted value is 572 L/min, but his personal best is 520 — which is completely normal and precisely why the personal best wins. His zones come from the 520: green at 416 and above, yellow from 260 to 415, red below 260. A morning reading of 450 puts him at 87% and firmly in the green zone, even though it is well under the predicted 572. Someone comparing that 450 against the predicted number instead would think they were having a bad day.

A 9-year-old, 130 cm, reading 210

Children get the height-based equation, so 130 cm predicts 250 L/min regardless of sex. A reading of 210 is 84% of that — green zone, but only just, and worth watching over the next few days. Children's numbers climb as they grow, so a child's personal best should be re-established every few months rather than treated as fixed. If night-time coughing is part of the picture, our guide to nebulizers versus inhalers covers how delivery devices differ for younger children.

Frequently asked questions

What is a normal peak flow score?

There isn't one normal number — it depends on age, height, and sex. A healthy adult typically falls somewhere between about 400 and 700 L/min, and a child between roughly 150 and 450 L/min, but the spread inside "normal" is wide. Enter your details above to see the predicted value for your own build, or read it off the chart table. Once you have two weeks of readings taken while you feel well, your personal best replaces all of it as the number that matters.

What is a good peak flow for my height?

Height is the strongest single predictor, which is why the chart above is laid out by height with age across the columns. For adults, each extra 5 cm adds roughly 16 L/min for men and 11 for women, while each decade of age costs about 25 and 18 respectively. For children under 15, height is effectively the whole equation — every 5 cm adds 25 L/min.

Is a peak flow of 250 low?

It depends entirely on who is blowing. For a 9-year-old of 130 cm, 250 is exactly the predicted value. For a 40-year-old man of 175 cm whose personal best is 520, a reading of 250 is 48% of best — red zone, and a medical emergency. This is the reason a single peak flow number in isolation means very little, and why the percentage of your own best is the figure to watch.

When should I worry about my peak flow?

Treat anything below 50% of your personal best as an emergency: take your quick-relief medicine and get help immediately, calling 911 if breathing doesn't improve quickly, you can't speak in full sentences, your lips or fingertips look blue, or you feel drowsy. Between 50% and 79% you're in the yellow zone — act on your asthma action plan and contact your clinician if you keep landing there. A gradual downward drift over several days is also worth a call, even if every individual reading still looks acceptable.

How do I find my personal best peak flow?

Take readings twice a day for two weeks during a stretch when your asthma is well controlled and you feel good — once in the morning and once in the early evening, before using an inhaler unless your clinician has told you otherwise. Blow three times at each session and record the highest of the three. The highest number across the whole fortnight is your personal best. The printable diary on this page is laid out for exactly that: four weeks of AM and PM rows.

Does my peak flow meter's scale change the number?

Yes, and it's a common source of confusion. Meters made to the older Wright scale and to the current EU / EN 13826 scale read differently for the same blow, and predicted-value tables exist for both. Use the same meter every time, establish your personal best on that meter, and compare all future readings against it — that sidesteps the scale question entirely.

Can I embed this peak flow chart on my own site?

Yes — copy the snippet at the bottom of this page. It's free for asthma educators, school nurses, respiratory therapists, clinics, and patient-support sites, with required attribution built in. No fee, no signup, and no analytics attached to the embed.

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Dr. Taylor's recommendations for peak flow monitoring

Everything on this page depends on a meter you trust and use consistently. Each link goes to the full review with current top picks, prices, and honest pros and cons:

• Best Peak Flow Meters — the device that produces every number above. Pick one, then stay on it, because switching meters resets your personal best.
• Best Pulse Oximeters — peak flow measures airflow; oxygen saturation measures the consequence. Read together they characterise a flare far better than either alone, and our guide to pulse oximeter readings explains how to interpret them.
• Best Steam Inhalers — warm moist air for the chest tightness and mucus that often accompany a yellow-zone stretch.

If a clinician has raised nebulized medication with you, read our current position on buying a nebulizer first — the category has changed considerably and the honest answer is no longer a simple product recommendation. Nebulizer types explained covers the compressor, ultrasonic, and mesh distinction if you already own one.

Sources & methodology

• Nunn AJ, Gregg I. New regression equations for predicting peak expiratory flow in adults. BMJ 1989;298(6680):1068–70 — the adult equations, valid for ages 15 to 85, as adapted by Clement Clarke for the EU / EN 13826 scale.
• Godfrey S, Kamburoff PL, Nairn JR. Spirometry, lung volumes and airway resistance in normal children aged 5 to 18 years. Br J Dis Chest 1970;64(1):15–24 — the height-based children's equation.
• American Lung Association. Measuring Your Peak Flow Rate. Updated January 2026 — the green / yellow / red zone system and measurement technique.
• Cleveland Clinic. Peak Flow Meter: How To Use, Measurement & Results. — the personal-best method (twice daily for two weeks while well) and worked zone example.
• Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample of the general U.S. population. Am J Respir Crit Care Med 1999;159:179–187 — the NHANES III reference set discussed above; cited for transparency, not used for the calculations on this page.

Every value in the chart above is generated from the published equations rather than transcribed, and the arithmetic is checked against 18 fixed test cases on every build. This tool is reviewed annually for citation currency. About Dr. Taylor · Last reviewed August 14, 2026.

Embed this tool on your site

Free for asthma educators, school nurses, respiratory therapists, clinics, and patient-support sites. Required attribution is included in the snippet. No fee, no signup, no analytics attached to the embed.

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