My dad told me to measure the volume of our garage, but I don’t know why. It seems kind of weird to me.
In the body, liquids accumulate. It can be the body of a cup, a body of a bucket, or the body of your body. Whatever it is, this body accumulation represents the volume of liquid in your body.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.