Measure chest for knitting

Can someone kindly tell me the proper steps to measuring your chest for a yarn sweater?

Here are the instructions for my project.

To Fit Chest: 22 (24, 26, 28, 30, 32)".
Finished Chest Measurement: 27 (28¾, 30½, 32, 34, 36)".

It looks like a child’s size, yes?

Measure around the widest part of the chest–under the arms.

I always like to measure a sweater that fits well and use the finished measurements of the pattern.

Yes, it’s probably better to measure a sweater that’s already being worn and isn’t too small. Then match it to the finished measurements on the pattern.

The difference in the two measurements is to allow for ease, which is what you allow to keep things from being skin tight. If you have a 32 inch actual chest measurement for this pattern you will allow for a 36 inch finished garment measurement, giving you 4 inches of ease.
For a child, the measurement of the largest part of the chest, a little below the armpits, would be the correct measurement.