If you've never taken an overarm measurement, or don't even know what it is, this topic probably wouldn't have meant very much to you until now. The Overarm measurement is just like the Chest measurement, except that you have the tape positioned OVER the customer's arms instead of under them. You should have the tape parallel to the floor, going over the largest part of the customer's chest and back.

If you do take this measurement for all of your MTM orders already, you've probably heard that if the customer's Overarm is greater than his Chest by 7 inches, he will need an alteration - or maybe you've heard 8 inches, or maybe even 9. What's the right number?

Depending on the size of the customer, any of the three answers might be correct. Below you'll find a chart that shows the average difference between a man's Chest and Overarm measurement, based on the size of the person. Simply put, the average difference isn't the same for every size. You shouldn't expect an 8 inch difference for a man who only weighs 120 pounds, and wears a size 36 jacket. If he does have an 8 inch difference, you'll likely need to move up to a larger size in order for the customer to feel comfortable. The chart shows which size to pick based on the Overarm-Chest difference. You shouldn't choose a size more than two larger (e.g. from North American size 41 to 43, or European size 52 to 54).

What causes a large difference between the Chest and Overarm? The most common cause is that the person has large biceps. The other common cause is that he has a wide back, causing his arms to rest at his sides further away from the side of his body than normal.

The diagram below illustrates why moving up to a larger size accomplishes the same thing as letting out the sleeve for a large bicep. To begin with, a larger size will already have a slightly larger sleeve simply because it's a bigger size. However, you'll also notice that in order to make a sleeve larger, you have to enlarge the under part of the armhole, which happens to be exactly where the Chest of the garment is, making the Chest larger as well. This explains why upsizing to a larger size works, because the sleeve AND Chest are larger.