Buying a suit online is easy enough, but buying a suit that fits well and looks good is a little more complicated. Though tailoring is an art, it’s also a science of sorts, with endless variables and numbers to input and weigh up.

“It is going to be a lot easier for someone that already has quite a few suits in their wardrobe than it is for someone who is a tailoring novice,” says Mats Klingberg, founder of one of London’s most sophisticated menswear stores, Trunk Clothiers. “But even so, it’s definitely something that everyone should consider.”

The key to ordering something that won’t leave you looking like you’ve raided your dad’s wardrobe (or worse, your teenage brother’s) is to conduct a little research before you make a single click. To help, we’ve compiled a comprehensive list of everything you need to know about buying a suit on the internet.

How To Buy A Suit Online: 4 Key Points

1. Know Your Measurements

Ordering a suit without measurements is like driving blindfolded. The simplest way of finding yours is to measure an existing suit that you like the fit of. “If the garment you’re looking at has similar measurements to one of your existing suits, you can be pretty confident that it will fit,” Klingberg explains. Most retailers have instructions for how they measure their garments, but in any case these are the general rules.

Trunk Clothiers

Chest: Lay the jacket flat with all buttons closed and run a measuring tape from armpit to armpit. If you don’t have a jacket that fits well, have someone measure around the broadest part of your chest (usually around nipple height), under your arms and level with the ground. Keep a finger between the tape and your body to allow for comfort.

Waist: Take a pair of trousers that fit well (jeans or chinos will work just fine) and lay them completely flat. Measure the waistband from edge to edge, and double the result to get your waist measurement. Otherwise, wrap the tape around the part of your body where your waistband usually sits.