By thirty seconds I mean the thirty seconds you spend staring helplessly at racks in a hire shop or the thirty seconds it takes someone on the phone at said hire shop or website with a size chart open before they ask you “and what size are you taking?” Not your jacket size. Not your shirt collar size. Your waistcoat size, as though you know this off by heart. You don’t, obviously you don’t. Unless you’re Tony Hadley. The waistcoat already picked out, colour sorted, wedding four weeks away and someone behind the counter or a blinking cursor on a dropdown menu asking you what size takes you.
Not.
You haven’t got thirty seconds, you’ve got about four, because someone’s waiting and the assistant is already grabbing the next rail.

This is the point, about eight years ago now, where I saw someone in front of me in Meadowhall mumble “medium, I suppose” through gritted teeth like it was an English question and he actually understood what was being asked of him.
He didn’t understand it. None of us do first time. I want to have words with the nineteen eighty eight me who bought a waistcoat too big to wear at anyone’s wedding because the shop only had two sizes and I thought bigger meant safer with button-up items. It doesn’t mean safer, it means you have a waistcoat that looks like a bib on top of your shirt. The huge confusion between sizes stems from two things really, and once you know these two things the irritating fitting room faffing doesn’t matter as much as you think it does.
Your chest measurement will do more lifting than you think, and British/ American sizing doesn’t help
Everyone latches onto the waistcoat size being the same number as your shirt size or jacket size and while that’s true in the first place – it’s your chest measurement in inches across the broadest part under your arms – it doesn’t account for British versus American sizes doing their best to make you hate yourself. Taken properly and not with three jumpers on like my brother did before his niece’s christening so he could spend the rest of the ceremony looking like he was howling at Jehovah in silent protest.
Chest measurement is correct but where it goes wrong for most people asking this question is that a 40inch chest doesn’t always equal the same waistcoat between brands. Some high street shops in the UK still go by S,M,L,XL etc rather than an actual number on the waistcoat itself while American sizes and a lot of online retailers shipping to the UK will use the actual inch count so you end up with a “Large” that says fits 42 to 44 inches right next to a “40” from another place that says fits 40 inches only. Both these systems aren’t wrong, they’re both telling you the truth about the chest size it fits, it’s just nobody clarifies which system you’re buying from when you go to order and you find yourself two waistcoats deep in a Tesco return pile wondering how you’ve gone up and down two sizes on the same afternoon despite measuring yourself on a bloody roll of toilet paper in the aisle.
Skip the letters completely if you can and find where the inch count is listed for chest on the product description because that number is far less subjective than S/M/L ever will be. Take your own measurement with a tape not a guess at what size you were in the last wedding you attended three years ago, we all change shape and most of us do it without noticing until we try something on and suddenly our confident Bing Crosby swagger is more Will Ferrel drunk uncle ambling, and do it over a shirt because that’s what you’ll be wearing it over. Then add nothing to it. None of this “rounding up for comfort” nonsense I used too. Unless you’re padding out for comfort a waistcoat should sit against your skin snugly, that’s what it’s there for. If you wanted something loose you’d get a bloody cardigan. UK v US probably doesn’t matter as much as finding that inch count but where I will give it points is American waistcoats do seem to cut slightly looser through the body to fit that chest size according to measurements I took on a couple bought online just to see if it was true, and it is. Caught me out when I bought a burgundy one for a nephew’s wedding that was size matched to my brother’s but cut fuller so looked like my brother had borrowed him Dad’s and lost half a stone before the ceremony. Your actual chest number will get you 90% of the way there, it’s everything else that lets you down.
Waistcoat length matters far more than waistcoat fit, and this is where people nearly always get it wrong.
Everyone talks about finding your chest number because that’s what all the labels seem to highlight. Except they never mention the bit that will make or break how your waistcoat looks on you which is the length of it. Seriously, this is why Wesley put a boot up Neil’s backside. I’ll explain why in a second but first, where waistcoat length is concerned you want the bottom point of it to just touch the top of your waistband, where your trousers and shirt meet. Nothing of your shirt should show below it when you get it right and it shouldn’t ride up over your trousers either.
Sounds obvious but you’d be amazed how many people ignore it. Too short and you end up with that flap of shirt showing whenever you move like I did at my mate’s wedding in Rotherham back in nineteen ninety something and spent the night awkwardly pulling my waistcoat down in the hope it would stretch out magically like one of his sidebirds’ dresses. Too long and it will bunch up over your belt when you sit down, looking more like something your Uncle borrowed than a tailored piece of clothing. Which is why the guy in Meadowhall looked wrong. Right fit across the chest thank you very much but as soon as he sat down at the top table everybody could see his waistcoat was too long.
Everyone ignores length because ninety percent of waistcoats bought off the peg use your chest measurement to size the length as well on the basis that someone with a sizeable chest is probably taller than average and vice versa. Guess how many people actually fit that ratio?

Six tenths?
Me neither. If you’re short with a large chest or tall and lean that “metric” sized against you every single time and no amount of getting your chest size perfect is gonna fix a waistcoat that’s two inches too short or long for your body. Length is by far the most important bit to get right and something I’d check before anything else, squeeze into it somewhere if you can before you buy because being sat down is where a poor fitting waistcoat shows it’s true colours. Standing up can hide half a dozen sins that will scream at you from the top of a chair.
Buy online and have no option to try anything? Measure a waistcoat you already own from shoulder seam down to where you want the bottom point to fall and use that measurement to double check against theetails the retailer gives you on their site. Sure, the size chart is handy but unless they list the waistcoat measurements separately scroll past it to where they hide that info. It’s always there if you dig for it.
Get your chest measurement right by using your own tape measure, and make sure you’ve got the length right by checking it covers your waistband perfectly and you’ve answered the actual question behind this whole thing. Which wasn’t “What’s the best way to…” it’s always;
“How do I stop buying the wrong bloody size? !”