Be honest, and don’t let the “measuree” try and influence your numerical judgement.
Make sure he is completely relaxed.
Start with the chest
With arms up and to the side (like the angel of the north) pass the tape measure horizontally around the chest until the end meets, holding the tape quite firmly around the body. Ask the gentleman to lower his arms to his side. This will give an accurate chest measurement.
Contrary to popular belief, the waist for a trouser is actually above the hip bone which are the bones you can feel on each side of the body. Particularly for a hire outfit this is where you should measure, but if it’s for a purchase measure lower if required. This should be less than the chest.
Measure quite firmly and make sure the gentleman is relaxed and not holding his breath to lower the numbers. He’ll want to be comfortable in his clothing.
ALWAYS IGNORE THE LABEL IN YOUR JEANS.
There are two ways of doing this:
Inside leg seam. If he’s wearing a good pair of trousers that fit you can take the inside leg by pushing the end of the tape measure up between the legs to the crotch or fork of the trouser and measure down the seam to the floor (without shoes) or above the heel (with shoes).
Outside leg seam. If he is in scruffs or shorts or the inside leg isn’t for you, then you can always measure the gentleman’s outside leg. Measure from the waist position on the outside of the body, where you measured his waist, down the outside seam to the floor or just above the heel.
This measurement is purely for the collar of a shirt. Just pass the tape around the neck, measuring firmly and then add half an inch or a centimeter and a half to make it comfortable. There’s nothing worse than a tight neck on an otherwise lovely shirt! This gives you an accurate collar size.
A height measurement is a handy one too, but not always necessary. If in doubt, ask the tailor or shop.