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# How do you measure vital capacity at the bedside?

###### Wiki User

The correct way the measure vital capacity is by using a spirometer.

It can also be estimated this way:

Vital Capacity can be measured with a string, calculator, ruler and balloon, believe it or not. Blow up the balloon and let it out a few times to stretch the rubber. Then take a very deep breath and blow out all the air that you can into the balloon. Tie it off. Pass the piece of string around the widest part of it to measure it. Using the ruler, measure the string. (My VC is very good, it's 4.2, and so my string was about 60cm long.) Divide the meaurement of the string by pi (if you don't have suitable calculator, you can divide by 3.14 on a standard calculator) and compare the number to this chart: Balloon diameter (centimetres:)

is your final number that you got by dividing by pi. Balloon diameter: Approximate vital capacity in litres:

8 0.3

9 0.4

10 0.5

11 0.7

12 0.9

13 1.2

14 1.4

15 1.8

16 2.1

17 2.6

18 3.0

19 3.6

20 4.2

21 4.8 Chart provided by Mark Ash, Graeme Lofts, Merrin J. Evergreen, on page 163 of the Jacaranda Science textbook Book 2.

Theoretical vital capacity:

Look for Vital capacity in Wikipedia for the formula. There are also online calculators.

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