A sport coat size has two parts: the number is your chest measurement in inches, and the letter or word is the length. A 48 Long fits a 48-inch chest on a man who needs a longer body and sleeve. A 50 Regular fits a 50-inch chest at standard length, and a 44 Extra Long (44XL) fits a 44-inch chest on a very tall frame. Here is how regular, long and extra-long compare head to head, and how to pick the right big and tall sport coat size on the first try.

The 30-second answer

1. Find the number. Measure your chest over a shirt, under your arms and straight across your shoulder blades. That measurement is your jacket size, per Westport's size chart.
2. Pick the length by height. Most makers put regular at about 5'8" to 6', long at about 6' to 6'3", and extra-long above that. The cutoffs move by an inch or two from brand to brand.
3. Check two things in the mirror. The jacket should cover your seat, and about a quarter-inch of shirt cuff should show past the sleeve.

Regular: built for a bigger chest at standard height

A regular-length coat is the right call if you are under about 6 feet. At Westport, regular sport coats run in chest sizes from 50 up to 58, depending on the coat, which is where most big-size customers land. If you wear big shirt sizes like 2XB or 3XB, a regular coat in your chest size is the usual starting point.

Long, as in a 48 Long: more body and sleeve for 6 feet and up

A long coat adds length to the body and the sleeve so the hem still covers your seat and the cuff still reaches your wrist. On Westport's current coats, long sizes also run from a 50 to a 58 chest. A man around 6'2" with a broad chest, the build that pulls a regular coat short at the back, usually lands in a long.

Extra-long: the tall, leaner frame

Extra-long (XL or X-Long) adds more length again. Westport carries extra-long sizes starting at a 44 chest, and that is the clue to who they are for: tall men with a trimmer build, often the same men who wear XLT or 2XT shirts. A man 6'4" or taller with a 46-inch chest wears a 46XL. In most current Westport coats, extra-long tops out around a 54 chest.

Head to head

Chest range at Westport. Regular and long: 50 to 58, depending on the coat. Extra-long: 44 to 54.

Body length. Each step from regular to long to extra-long adds length so the jacket covers your seat. If the hem stops at your belt, you need the next length up.

Sleeve. Each step also adds sleeve length. A tailor can shorten a sleeve easily, but only a little length can be let out, so when in doubt, size up in length rather than down.

Who it fits. Regular for big men under about 6 feet. Long for big men from about 6' to 6'3". Extra-long for tall men over that, especially with a leaner build.

What about knit blazers?

Soft, unstructured knit blazers often skip the chest-and-length system and use shirt sizes instead. The Westport Black Tribeca Popcorn Stitch Blazer, for example, comes in tall sizes LT to 4XT and big sizes 2XB to 4XB. If a coat is listed that way, buy the size you wear in a sport shirt. Our guide to big and tall business casual shows how to wear both styles at the office.

So, which one should you buy?

Start with your chest measurement and your height, then try the jacket on with the shirt or sweater you plan to wear under it. Button the top button and reach both arms forward. If the back pulls or the cuffs ride halfway up your forearm, go up a length. If the jacket covers your seat but hangs loose through the chest, go down a size number. Browse every length in our big and tall sport coats, or see how to find a suit that fits for the full tailoring picture.