Measuring the weight of your head involves effectively isolating it from the rest of your body.
Decapitation has the obvious disadvantage of your not being alive to see the results. However, there is a solution.
Your neck vertebrae are responsible for holding your head’s weight. If you hang upside down from your feet the vertebrae in your neck move apart slightly because of the weight of your head pulling on them.
To weigh your head you must simply lower yourself slowly onto a scale while hanging upside down.
You continually observe the distance between the top vertebra of your neck and your skull, using, say, an ultrasound scanner, and the instant the vertebra starts moving toward the skull you stop and read the scales.
Because your neck is not imparting any force on to your head, this isolates your head from your neck, thus giving an accurate measure of your head’s weight.
When learning how to do an Eskimo roll when kayaking, instructors usually tell their students to make sure that however much they needed a breath, the last thing to leave the water as your body emerged should be your head. They say the average human head weighs around 10 pounds.
Unfortunately, our head is a lot of extra weight to lift clear of the water using only the blade of a paddle.
The human head does weigh a fair bit.
We aren’t able to measure the weight of a head directly but we can measure its volume and guess its density on the assumption that the brain, like the rest of the body, is mostly water and we know the density of water at 32°F.
To measure the volume of the head, find a suitable bald volunteer, and lower his head into a bucket of water filled to the brim.
The water should be as close to 32°F as the volunteer can bear and his head lowered vertically and crown downward until the water reaches the base of the chin. The water that spills over the sides of the bucket is collected in a larger bowl in which the bucket is standing, and its volume measured.
This is repeated five times so we can obtain an average.
The average volume of water displaced is about 260 cubic inches, giving an estimate of the weight of a human head at 9.4 pounds.