How Do I Find My Size in Jackets?

By Ella Blake, Tellar Stylist

Finding your size in jackets is genuinely one of the trickiest bits of dressing yourself — and I say that as someone who has styled women for years and still occasionally ends up with something that pulls across the shoulders or swamps me entirely. The short answer: jacket sizing is not the same as your dress or top size, and the brand you're buying from makes an enormous difference. Once you understand a few key things, it all becomes much simpler.

Why Jacket Sizing Feels So Confusing

Here's what nobody tells you upfront: jackets are sized with ease allowance built in. That means there's extra room factored in so you can move your arms, sit down comfortably, and — crucially — layer underneath. A tailored blazer, a chunky puffer, and a classic trench are all "jackets," but they're cut completely differently. Comparing sizes across them is almost meaningless without knowing the fit intention.

I learnt this the hard way when I ordered a gorgeous camel blazer from Reiss in my usual size 12, only for it to feel like I'd borrowed my sister's jacket. Turns out I needed to size down because Reiss cuts with a relaxed, fashion-forward ease. The reverse happened to me with a Barbour wax jacket — sized up from my norm and it still felt snug across the back once I had a chunky knit underneath. The point is: brand and style matter just as much as the number on the label.

The Measurements That Actually Matter for Jackets

Forget your height and weight for a moment. For jackets, these are the three measurements you actually need:

Bust / chest: Measured at the fullest point, arms relaxed at your sides. This is your primary sizing number for most jackets.
Shoulder width: From the tip of one shoulder to the other, across your back. This is the measurement that cannot be easily altered — if the shoulders don't fit, nothing else will.
Back length: From the base of your neck to where you want the hem to sit. Particularly important for longer coats and blazers.

If you're between sizes, always size up on a structured jacket — you can nip in the waist with a belt or have it taken in, but you cannot let out tight shoulders without a full alteration. I always tell clients: buy for your widest measurement, then tailor from there.

How to Measure Yourself Properly

You need a soft tape measure (the kind you find in any sewing kit) and ideally a friend to help. Here's the quick method:

Wear a fitted top or bra — no oversized jumpers that will throw off your numbers.
Stand naturally, arms slightly away from your body for the bust measurement.
Keep the tape parallel to the floor for bust and hip — it has a habit of dipping at the back.
Measure twice. Seriously, always measure twice.
Note your measurements in centimetres and inches — UK size guides often use both.

Understanding Jacket Fit Types

Not all jackets are cut the same way, and understanding the intended fit helps enormously when choosing your size:

Tailored / slim fit: Designed to follow your body closely. Often cut narrower in the shoulder and waist. Brands like Massimo Dutti and Me&Em tend to cut in this way — elegant, structured, and worth checking their size guide carefully.
Relaxed / oversized: Intentionally roomy. Brands like All Saints and Boden often offer this in their outerwear. You may want to size down from your usual.
Regular / classic fit: The middle ground — room to layer but not intentionally oversized. Hobbs and Phase Eight tend to sit here, making them reliable for consistent sizing.
Technical / outdoor fit: Built with extra room for layering and movement. Think Barbour and outdoor-inspired brands — you typically need your actual bust measurement plus a few centimetres for layering allowance.

Brand Quirks Worth Knowing

After years of testing this stuff, here's what I've found about specific brands when it comes to jacket sizing:

Jigsaw — tends to run slightly generous in the shoulder. If you're narrow-shouldered, check the shoulder measurement specifically before ordering.
Ted Baker — uses a numbered sizing system (0–5) rather than standard UK sizes. Their fit guide is genuinely good; use it.
Hobbs — reliably true to size in tailoring and coats. One of my most trusted brands for consistent sizing.
Massimo Dutti — cuts slim in the body, especially blazers. Go up one size if you have a fuller bust or like a little room to move.
Barbour — their classic wax jackets run small and narrow. Many women size up by one or even two for layering. Their website has specific layering guidance, which is worth reading.
Phase Eight — consistently well-cut for a UK figure. True to size across most of their outerwear range.
Me&Em — premium quality with a London-chic fit. Tailored pieces can feel narrow across the back. Check reviews per style.

Two Independent Brands Worth Knowing

I love championing smaller brands here, because they often offer exceptional fit and quality that the high street can't match:

Rino & Pelle — a Dutch brand with beautiful faux fur and textured coats. Their sizing is European-based, so go by their measurement chart rather than your UK size. Incredibly flattering cuts and brilliant for curvier figures.
Beaumont Organic — a sustainable British brand making beautifully structured jackets and coats in natural fabrics. They size true to standard UK measurements and the quality is exceptional for the price point. Worth every penny.

What to Do When You're Between Sizes

This is genuinely the question I get asked most. My advice:

If the size difference is in the bust — size up. A jacket that pulls across the chest looks wrong instantly.
If the size difference is in the waist — size for your bust and use a belt, or have the waist taken in. Easy alteration.
If it's the shoulders — this is where it gets tricky. For structured jackets, the shoulder seam must sit exactly at the edge of your shoulder. If it droops or sits on your arm, the jacket is too big regardless of how it fits elsewhere.
For puffers and casual outerwear, you generally have more flexibility — these are designed with movement in mind.

Stop Guessing Your Jacket Size — Let Tellar Do It For You

This is exactly why Tellar exists. It's the UK's leading free sizing tool, and it takes the guesswork completely out of shopping for jackets (or anything else, frankly). You enter your measurements once — bust, waist, hips, or simply your existing size in a brand you know well — and Tellar instantly matches you to your correct size across 1,500+ brands.

No more cross-referencing size guides. No more ordering two sizes and returning one. Just your size, in the brand you want, in seconds.

Use the Store Size Lookup tool to find your exact size in brands like Barbour, Reiss, Hobbs, Massimo Dutti and hundreds more.
It's completely free — no app to download, works straight in your browser.
Measure once, shop confidently forever.

And if you want to go deeper on sizing and fit across everything in your wardrobe, the Ultimate Clothing Sizing Guide on the Tellar Fashion Hub is a brilliant resource — honest, unbiased, and completely free.

While you're there, check out the Ultimate Guide to Jackets & Best Buys — it covers styles, body shape matching, and brand recommendations in serious detail. The Tellar Fashion Hub is stacked with posts from our stylists covering every fashion query you could think of. Honest. Unbiased. Independent. Always free.

The Bottom Line

Finding your size in jackets comes down to three things: knowing your key measurements (especially your bust and shoulder width), understanding the fit intention of the style you're buying, and checking the specific brand's size guide rather than assuming your usual size will translate. Once you've got those three things nailed, jacket shopping becomes a whole lot less painful — and a whole lot more fun.