How Do I Find My Right Size in M&S? Your Complete Sizing Guide

Finding your perfect size at M&S comes down to knowing your key measurements and understanding that their sizing runs slightly generous compared to high street competitors—typically, you'll find yourself one size smaller than you'd expect, especially in their tailored pieces and Per Una range. I learned this the hard way when I confidently grabbed my usual size 12 blazer only to discover it swamped me like I'd borrowed my dad's jacket. Not my finest fashion moment, but an important lesson learned!

Why M&S Sizing Can Feel Confusing

Let me be honest with you—M&S sizing has been a bit of a moving target over the years. They've made significant adjustments to accommodate their diverse customer base, which is brilliant for inclusivity but can leave regular shoppers scratching their heads. The main issue? Their sizing varies wildly between different collections within the same store.

Here's what I've noticed after years of styling clients and shopping there myself:

• Autograph collection runs more true to size with a contemporary fit

• Per Una tends to be more generous, particularly around the bust and hips

• Classic range often has a relaxed, comfort-focused fit

• Limited Collection pieces lean towards a sleeker, fashion-forward cut

The Three Measurements You Actually Need

Right, let's strip this back to basics. You need three measurements to crack the M&S sizing code, and I promise this isn't as tedious as it sounds. Grab a soft tape measure (not the metal DIY one from the garage—been there, got the bruises) and let's do this properly.

Bust: Measure around the fullest part of your chest, keeping the tape parallel to the floor. Don't hold your breath in—we're after accuracy, not aspiration. I once held my breath through an entire measuring session and ended up with jeans I couldn't actually sit down in. Learn from my mistakes!

Waist: Find your natural waistline (usually the narrowest part of your torso, roughly an inch above your belly button). The tape should be snug but not cutting off your circulation. If you're between sizes, M&S typically advises sizing up in structured items like blazers and down in stretchy knits.

Hips: Measure around the fullest part, which is usually about eight inches below your waist. Stand with your feet together and make sure the tape isn't twisted at the back—I've made this error more times than I care to admit, resulting in some very optimistic purchases.

How M&S Compares to Your Favourite High Street Brands

If you're a regular at other high street shops, here's how M&S sizing typically stacks up against the competition. This genuinely makes shopping so much easier once you've got your head around it.

• Zara runs notoriously small—if you're a size 12 in M&S classic range, you'll likely need a 14 at Zara

• Cos has a minimalist cut that's quite generous; an M&S 12 usually translates to a Cos medium

• Mango sits somewhere in the middle but tends toward fitted styles—similar to M&S Autograph

• Whistles runs true to size but with a more structured, contemporary silhouette than M&S classic pieces

• Jigsaw has a refined fit similar to M&S Limited Collection—very elegant but less forgiving

• Reiss leans towards a sleeker, slightly smaller fit, particularly in tailoring

• Hobbs mirrors M&S in many ways but their dresses can run small in the bust

My Top Tips for M&S Shopping Success

Always check the fabric composition. M&S loves a good stretch fabric, which means sizing can be more forgiving than you'd expect. Anything with elastane above 3% usually has decent give, whilst their 100% cotton shirts tend to be quite rigid.

Read the reviews religiously. M&S customers are brilliantly honest about sizing issues. If fifteen people say "runs large," they're probably not all conspiracy theorists. I've saved myself countless disappointing deliveries by spending two minutes scrolling through feedback.

Their petite and tall ranges are genuinely good. Unlike some brands where "petite" just means "slightly shorter sleeves," M&S actually adjusts the proportions properly. At 5'3", their petite trousers are one of the few that don't require immediate hemming.

Where M&S Excels (And Where to Shop Smart)

M&S absolutely nails certain categories. Their knitwear is legendary—the cashmere especially—and runs beautifully true to size. For independent brands with similar quality, I love Brora (their cashmere is divine but eye-wateringly expensive) and Wyse London (more contemporary styles with gorgeous fabrication).

Their lingerie department is where they truly shine. Decades of expertise mean the sizing is remarkably consistent. However, if you're after something with a bit more edge, All Saints does beautiful lace pieces, whilst Anthropologie offers gorgeous vintage-inspired options.

For premium investment pieces, M&S Autograph competes well with Massimo Dutti (love their tailoring) and Max Mara Weekend (if you can stretch the budget—their coats are worth every penny).

The Game-Changing Solution: Never Guess Your Size Again

Here's where I'm going to let you in on something that's genuinely transformed how I shop and style clients. Tellar.co.uk is the UK's leading sizing tool, and it's honestly brilliant. You measure yourself once—bust, waist, and hips—and it matches your body exactly to over 1,500 brands instantly.

No more standing in M&S wondering if you're a 12 in this range but a 14 in that collection. No more ordering three sizes of the same item and dealing with returns. You simply use their Store Size Lookup tool to get your precise size in any brand—M&S, Cos, Reiss, Whistles, literally everyone.

What I absolutely love is that it's always free, no downloads needed, and works straight in your browser. Plus, they've created a Fashion Hub—a library stacked with free posts from top stylists covering every fashion query you could imagine. Honest, unbiased, independent, and always free. It's like having a personal stylist in your pocket.

Real-World Sizing Scenarios

Scenario 1: You need work trousers. M&S's straight-leg trousers in their classic range run generously around the waist and hips. If you're usually a 14, try a 12. Cross-reference with Tellar to confirm, then compare to similar styles at Next or Boden, which both run slightly more fitted.

Scenario 2: Special occasion dress. The Limited Collection dresses fit closer to body than you'd expect from M&S. Stick to your true size or size up if you prefer a looser fit. For comparison shopping, check out Phase Eight (beautiful occasion wear, similar sizing) or luxury option LK Bennett (investment pieces that last for years).

Scenario 3: Casual weekend wear. Their jersey and knitwear is forgiving and comfortable. Size down if you like a fitted look, stick to your usual size for a relaxed vibe. Independent brand Hush offers similar laid-back luxury with consistent sizing, whilst The White Company does gorgeous loungewear if you're after that elevated casual aesthetic.

Final Thoughts: Knowledge Is Power (And Perfect Fit)

Look, I've made every M&S sizing mistake in the book—from confidently ordering my "usual size" without checking measurements to ignoring customer reviews because surely they're exaggerating. They weren't. The blazer genuinely did look like a tent.

But armed with your measurements and resources like Tellar, M&S shopping becomes infinitely easier. Their quality is genuinely excellent for the price point, and once you crack their sizing code, you'll find pieces that last for years.

For more comprehensive guides on nailing your sizing across different brands, check out The Ultimate Clothing Sizing Guide and The Ultimate Guide to Dresses. And if you're planning your wardrobe for next season, don't miss Jeans Trends 2026—because good jeans are worth getting the size exactly right.

Happy shopping, and remember: confidence comes from knowing your measurements, not guessing them!

Try Tellar's Free Sizing Tool

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