How Do I Find My Size in Classic Shirts?

By Ella Blake, Tellar Stylist

Finding your size in a classic shirt is genuinely one of the trickiest things in women's fashion — and yes, I'm including wrap dresses and wide-leg trousers in that comparison. The classic shirt was designed for a male body. It's been adapted, tweaked, and reinvented for women over the decades, but the fundamental fit challenges remain: the bust, the shoulders, and that blasted gap between the buttons. Once you crack the code though? A well-fitted shirt is the most versatile thing in your wardrobe. So let's talk about how to actually get the right size.

Why Women's Shirt Sizing Is So Complicated

Here's the honest truth: most women's shirts are sized using broad labels — XS, S, M, L — with very little standardisation between brands. One brand's size 12 is another's size 16. I've stood in changing rooms genuinely baffled, holding two shirts in the same nominal size that fit completely differently. It's not you. The system is genuinely broken.

The main culprits are:

The bust — the most common fit issue. If you're over a B cup, you'll often find shirts gap at the chest even when the shoulders fit perfectly.
The shoulders — shoulder seams should sit exactly at the edge of your shoulder bone. Too wide and the whole shirt loses its shape; too narrow and it restricts movement.
The back length — crucial if you're going to tuck. Too short a back hem and it comes untucked the second you move.
The sleeve length — often an afterthought, but an inch too long throws off even a perfect fit everywhere else.

The Three Measurements You Actually Need

Before you buy anything — online or in person — get these three measurements down. It takes five minutes and will save you so many returns.

Bust: Measure around the fullest part of your chest, keeping the tape parallel to the floor and not too tight. This is your primary measurement for shirts.
Shoulder width: Measure from the edge of one shoulder seam to the other across your back. This is less commonly listed but incredibly useful when a brand provides it.
Back length: Measure from the nape of your neck down to where you want the shirt to finish. For a tucked shirt, you want this to be at least hip length.

I'll be honest — I didn't start doing this until I'd wasted a small fortune on shirts I never wore. The shirt that changed my mind was a beautiful Massimo Dutti linen piece I ordered online in my usual size. The shoulders were off by a centimetre and I could never get it to sit right. Had I checked the shoulder measurement against their size guide, I'd have sized up. Lesson very much learned.

The Bust Gap Problem — And How to Deal with It

If you have a larger bust, you already know the horror of the button-front shirt. The buttons pull, the fabric puckers, and the whole thing looks messy regardless of how expensive it was. There are a few practical solutions:

Size up in the body and have the shoulders and waist taken in by a tailor — this is genuinely worth the £15–£25 investment on a shirt you'll wear for years.
Look for shirts with darts — the small sewn folds that add shape through the chest and waist. They're your best friend.
Choose a stretch fabric blend — a small percentage of elastane makes an enormous difference to how a shirt sits across the bust.
Consider popover or half-button styles — these skip the full button placket altogether and are far more forgiving.

Whistles is one of the few high street brands that consistently cuts shirts with a proper bust allowance. Their relaxed Oxford shirts in particular are brilliant for fuller busts because the cut is generous through the chest without being boxy through the shoulders. Jigsaw is another one to check — their shirts tend to have a more shaped, intelligent cut that works well across different body types.

Brand-by-Brand: Where to Shop for the Best Fit

High Street Picks

M&S — consistently reliable sizing and great for petite, regular and tall options. Their pure cotton and linen shirts are a perennial bestseller for good reason.
Next — offer shirts across a wide size range and their fit guide online is actually one of the better ones. Good for long-length options if you prefer shirts untucked.
Mango — brilliant for current silhouettes. Their oversized and boyfriend-cut shirts run generous, so size down if you want structure.
Cos — precise, minimal cuts with excellent fabric quality. Their sizing is slim and structured, so measure before buying — particularly through the shoulder.
Anthropologie — offers a wider range of cuts and fabrics than most, with helpful customer reviews that give real insight into how each style fits.
Me&Em — one of the best for a proper classic shirt that holds its shape. Pricier than your average high street, but the quality is worth it. Their fitted cotton shirts are a staple in my wardrobe.
Reiss — smart, tailored shirts that sit in the premium-high-street sweet spot. Their shirts run true to size with excellent shoulder construction.

Premium Options

Massimo Dutti — luxurious fabrics (think fine poplin, linen blends, and silk-cotton mix) at a mid-range price point. Their shirts consistently photograph and wear beautifully.
Hobbs — understated, elegant and built for grown-up dressing. Great for work shirts that don't look like you're trying too hard.

Independent Brands Worth Knowing

Emma Willis — a small, London-based shirtmaker who produces genuinely beautiful shirts with an optional made-to-measure service. If you've struggled to find shirts that fit your bust, this is the answer. Not cheap, but transformative.
Sirplus — a slow fashion brand making considered, slightly oversized shirts from deadstock and upcycled fabrics. Every piece is one-of-a-kind and the sizing is relaxed and inclusive. A genuinely lovely find.

Oversized vs Fitted: Which Sizing Approach to Take?

This matters more than people realise. If you're buying an oversized shirt — the kind you'll wear over a slip dress, knotted at the waist, or hanging loose over wide-leg trousers — you can size up from your bust measurement and not worry too much about precision. The whole point is the relaxed drape.

For a fitted or tailored shirt — the kind you'll tuck into trousers or wear open over a bralette — you need to be much more precise. Go by your bust measurement first, then check the shoulder. If in doubt between two sizes, try both. The shoulder seam is non-negotiable; it cannot be altered easily. Everything else can.

One Last Thing: Don't Ignore Fabric

A 100% cotton shirt in a stiff poplin will feel completely different to the same cut in a cotton-modal blend. Stiffer fabrics will feel smaller; softer fabrics will drape and stretch slightly. It's worth factoring in when you size — and always, always check the care instructions before you buy. There is nothing worse than a beautiful shirt that shrinks after one wash.

Find Your Perfect Shirt Size with Tellar

Sizing frustration is exactly what Tellar.co.uk was built to solve. It's the UK's leading free sizing tool — enter your measurements once and get your precise size across 1,500+ brands instantly, no size guide faff required.

Use the Store Size Lookup to find your exact fit at brands like COS, Reiss, Whistles and more — before you even add to basket.
Works in-browser, completely free, no download needed.
Want to go deeper? The Ultimate Clothing Sizing Guide covers every category — including, yes, shirts.
And if you're building a wardrobe from scratch, start with the Ultimate Guide to Jackets — it's a brilliant companion read.

Tellar's Fashion Hub is stacked with free, honest, stylist-written advice. No ads, no sponsorship, no agenda — just good fashion guidance, always free.