Most measurements can be taken with a taylors tape. If you do not have one then you can use a string, then measure the string with a measuring tape or ruler.
Here are instructions on how to make a homemade caliper for those who do not have one to measure with. https://3dcauldron.com/pages/homemade-calipers This is useful for width measurements such as head, shoulders, ect.
NOTE: We only need the measurements relative to the item you are purchasing.
Here is a video detailing how to properly take measurements.
Head
Note: It is more accurate to use calipers and measure width (ear to ear), depth (nose to back), and height (chin to top).
Neck
Upper Torso
Biceps
Forearms
Stomach
Waist
Thighs
Calves
