Measuring breathing and lung volume

How much air do you breathe? Scientists measure breathing and use models to explain how it works.

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Lung volumes

Tidal volume: the volume of air breathed in or out in one normal breath, about 0.5 litres at rest.
Vital capacity: the most air you can breathe out after breathing in as deeply as you can. It is several litres in an adult.
Breathing rate: breaths per minute. Count breaths for a minute, or for 30 seconds and double it.
Volume of air per minute = tidal volume × breaths per minute.

Exercise and measurement

During exercise, muscles need more oxygen and make more carbon dioxide, so breathing rate and tidal volume both go up.
A spirometer measures lung volumes. A peak flow meter measures how fast you can breathe out, and helps people with asthma check their airways.
Regular exercise strengthens the breathing muscles, so the vital capacity can increase.

The bell jar model

A model can show how breathing works.
Pull the sheet down: the volume inside increases, the pressure falls, and air rushes into the balloons. Limitation: the jar cannot move like the ribs, and there are no rib muscles.
Part of the modelRepresents
Bell jarChest (rib cage)
BalloonsLungs
Y-shaped tubeTrachea and bronchi
Rubber sheetDiaphragm
Worked example

At rest, Sam's tidal volume is 0.5 litres and he takes 12 breaths a minute. How much air does he breathe in each minute?

  1. Volume per minute = tidal volume × breaths per minute
  2. 0.5 × 12

Answer: 6 litres

Key idea

Tidal volume: one normal breath (about 0.5 L at rest). Vital capacity: biggest breath out. Air per minute = tidal volume × breathing rate. Exercise increases both. The bell jar model shows how volume and pressure changes move air.

Common mistakes
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Extra practice

2 more questions

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  1. Sam counts 8 breaths in 20 seconds. What is his breathing rate in breaths per minute?

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    Answer: 24 breaths per minute

    60 ÷ 20 = 3, so 8 × 3 = 24 breaths per minute

  2. At rest, Mia's tidal volume is 0.5 litres and she takes 12 breaths a minute. How many litres of air does she breathe each minute?

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    Answer: 6 litres

    0.5 × 12 = 6 litres

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Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.