# Peak Flow Calculator (Predicted PEF and Asthma Zones)

URL: https://speedycalculator.com/calculators/health/peak-flow/
Last updated: 2026-10-30

> The peak flow calculator predicts your normal peak expiratory flow from age, sex and height (Nunn and Gregg for adults; height-based for children), and puts your reading in the green, yellow or red asthma action-plan zone.

## Inputs

- Person
- Sex
- Age (years)
- Height (cm, in, m, ft, mm)
- Your peak flow reading (L/min)
- Personal best (optional) (L/min)

## Results

- Predicted peak flow
- Reading as % of reference
- Yellow zone starts below
- Red zone starts below

## Formula

```
Men: PEF (L/min) = ((height m × 5.48) + 1.58 − age × 0.041) × 60
Women: PEF = ((height m × 3.72) + 2.24 − age × 0.03) × 60
Children: PEF ≈ (height cm − 100) × 5 + 100
Zones: green ≥ 80% · yellow 50–79% · red < 50% of predicted or personal best
```

## Explanation

Peak flow meters measure how fast you can blow air out. Comparing readings with your personal best (or the predicted value) helps detect asthma attacks early and guide treatment in an asthma action plan.

### How to use the Peak Flow Calculator

- **Person**
- **Sex**
- **Age**
- **Height**
- **Your peak flow reading**
- **Personal best (optional)**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter your details and your best of three peak flow blows. Use your personal best instead of the predicted value if you know it.

### Inputs explained

FieldWhat to enterPersonChoose one: Adult, ChildSexChoose one: Male, FemaleAgeIn yearsHeightUnits: cm, in, m, ft, mmYour peak flow readingIn L/minPersonal best (optional)In L/min

### Example values

How the main result changes when **Age** changes and everything else stays at the example values above:

Age (years)Reading as % of reference (%)17.57226.2574357743.758052.5837090
*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — Person: Adult; Sex: Male; Age: 35 years; Height: 175 cm; Your peak flow reading: 450 L/min; Personal best (optional): 0 L/min.

Results — Predicted peak flow = 584 L/min; **Reading as % of reference = 77 %**; Yellow zone starts below = 467 L/min; Red zone starts below = 292 L/min.

## Key terms

- **PEF**: Peak expiratory flow.

## FAQ

**What is a normal peak flow?**
It depends on age, sex and height – often 400–650 L/min for adult men and 300–470 L/min for women.

**Should I use predicted or personal best?**
Personal best, measured when your asthma is well controlled, is more useful.

**What should I do in the red zone?**
Take your reliever and seek urgent medical help.


## Sources

- [Nunn AJ, Gregg I. New regression equations for predicting peak expiratory flow in adults. BMJ, 1989](https://pubmed.ncbi.nlm.nih.gov/2497789/)
- [NHLBI – Asthma action plan](https://www.nhlbi.nih.gov/health/asthma/action-plan)