How to Find Your Size in Formal Clothes — Without the Fitting Room Panic

By Ella Blake, Tellar Stylist

Finding your size in formal clothes is genuinely one of the most frustrating things in fashion — and it doesn't get easier just because you've been dressing yourself for decades. Formal sizing is a different beast to casualwear, and unless you know what you're measuring and what to look for, you can end up in something that technically "fits" but looks completely wrong on your body. Here's how to crack it, once and for all.

Why Formal Sizing Is Different

This is something I wish someone had told me years ago. I once bought a blazer in my "normal" size from a well-known brand, wore it to a job interview, and spent the entire meeting tugging at the sleeves because the shoulder seam sat halfway down my arm. It was technically my size — just completely the wrong cut for my frame.

Formal clothes — suits, blazers, tailored trousers, structured dresses — are built around specific proportions. The fit matters enormously because there's no stretch to hide issues. A denim dress can forgive a lot; a tailored suit jacket absolutely will not. The result? You need to measure properly, understand which numbers matter, and know which brands are worth trusting for your particular shape.

The Measurements That Actually Matter for Formal Wear

For most casual shopping, bust and hip get you through. For formal wear, you need to be more precise. Here's what to measure:

• Bust — measure at the fullest point, bra on, tape parallel to the floor

• Waist — your natural waist (the narrowest point, usually just above the navel)

• Hips — fullest point, usually about 8 inches below the waist

• Inseam — critical for formal trousers; measure from the crotch seam to the ankle bone

• Shoulder width — from shoulder point to shoulder point across the back; this is the one most people skip and the one that causes the most misery in structured jackets

• Back length — base of your neck to your natural waist; important for suit jackets and tailored tops

Write these down. Put them in your phone. You'll thank yourself later.

Suits and Blazers — Where to Start

Suits are where sizing gets most complicated, because the jacket and the trousers often need to be completely different sizes. That's not a problem with your body — it's just how tailoring works. Many brands now offer separates so you can mix sizes, which is genuinely brilliant.

For a blazer, always fit to the shoulders first. Everything else — the body, the sleeves — can be taken in or let out by a tailor. Shoulders cannot. If you've found a jacket where the shoulder seam sits perfectly and everything else is slightly off, buy it anyway and spend £30 on minor alterations. It'll look a thousand times better than a jacket that technically fits everywhere except the shoulders.

Brands that consistently deliver well-proportioned suiting for women include:

• Reiss — excellent tailoring, beautifully structured blazers, runs slightly small so size up if in doubt

• Massimo Dutti — one of the best on the high street for suiting, with incredible fabric quality for the price

• Hobbs — brilliant for hourglass and pear shapes, and their sizing is very consistent

• Phase Eight — particularly good for formal occasion dressing, solid size range

• Me&Em — chic, minimal, grown-up tailoring; their blazers are a particular highlight

Formal Dresses and Occasion Wear

For a structured occasion dress, measure your bust, waist, and hips, then check the brand's size guide rather than assuming. Size guides are genuinely different brand to brand — a 12 at one retailer is often a 14 at another.

Watch out for the "standard length" trap. Most formal dresses are designed for someone 5'7"–5'8". If you're petite, a midi will hit mid-calf (not ideal). If you're taller, a midi might read more like a knee-length. Always check the model height in product photos and cross-reference with your own.

• LK Bennett — their occasion dresses are impeccably cut and the sizing is reliable; consistently brilliant for formal events

• Coast — a go-to for occasion wear, especially if you want something that doesn't need extensive alterations

• Whistles — elegant, understated formal dressing done well; their dresses run true to size

• Ted Baker — cut well for those with curves; their sizing runs small so always size up

Two Independent Brands Worth Knowing

Beyond the high street, two labels I'd genuinely recommend for formal sizing done properly:

• Seferia London — a small London-based label specialising in tailored occasionwear for women, with detailed size guidance and a brilliant range of fits for different body proportions. Their sizing advice online is genuinely helpful.

• Birdsong — a London-based ethical brand using size-inclusive patterns. Their structured pieces are made with real bodies in mind, and they offer an unusually wide range of sizes in formal styles.

The Golden Rules of Formal Fit

• If the shoulders don't fit, walk away — no amount of styling will fix a dropped shoulder seam

• Fit to your largest measurement and tailor down where needed

• Always check brand-specific size guides rather than assuming your usual size translates

• Try on in a well-lit room (not a badly lit changing room) so you can see the actual fit clearly

• Budget a small amount for alterations — even £20–£40 of tailoring can transform an outfit that's "almost right" into one that looks custom-made

How Tellar Makes This Much Easier

Stop Guessing Your Size — Use Tellar

All of the above still requires you to know how your measurements translate across different brands — and that's where most people get stuck. That's exactly the problem Tellar.co.uk was built to solve.

Tellar is the UK's leading free clothing sizing tool. You measure once — bust, waist, hips, or just your existing size in a brand you already own — and Tellar instantly matches your body to the right size across 1,500+ brands. No more size guide archaeology. No more hoping for the best.

• Use the Store Size Lookup tool to get your precise size at brands like Reiss, LK Bennett, Hobbs, Coast, Me&Em, Ted Baker and more

• Read the Ultimate Clothing Sizing Guide for everything you need to know about how sizing actually works

• Explore more in the Ultimate Guide to Jackets & Best Buys — especially useful if you're shopping for suiting

It's completely free, works in-browser, and no download is needed. Honestly, it's the tool I wish had existed years ago — it would have saved me from that interview blazer disaster.

Formal dressing doesn't have to mean a stressful guessing game. Measure properly, fit to your largest measurement, don't skip the shoulder check, and let Tellar do the brand-by-brand size translation for you. You'll actually look forward to getting dressed.