How Do I Find My Size in Jumpers? A Stylist's Honest Guide

Finding your size in jumpers comes down to four key measurements: bust/chest, shoulder width, sleeve length, and body length — but the tricky part is that every brand sizes differently, and a "medium" in one can feel like an entirely different garment in another. I've been there. I once ordered what I thought was a cosy oversized knit from a brand I'd never tried before, and what arrived looked more like a crop top on me. Not the vibe I was going for. Let me save you the trouble.

Start With Your Measurements (Not Your Usual Size)

Forget what size you normally pick up off the rail. When it comes to knitwear, your actual body measurements are far more useful. Here's what to measure:

Bust/Chest: Measure around the fullest part of your chest, keeping the tape parallel to the floor. This is your most important number for jumper sizing.
Shoulder width: Measure from the edge of one shoulder to the other across your upper back. This matters particularly for fitted knits and structured styles.
Sleeve length: From your shoulder point to your wrist, with your arm slightly bent. Under-rated measurement, but a too-short sleeve is one of my biggest pet peeves.
Body length: From the top of your shoulder to wherever you want the hem to hit. Crucial if you're petite or tall.

Once you have these, cross-reference them with the brand's size guide — not just the generic S/M/L labels. It takes an extra two minutes and saves a lot of return faff.

The Fit Intention Matters More Than You Think

Here's something I wish someone had told me earlier: before you even look at measurements, think about how you want the jumper to fit. Knitwear is unique because fit is part of the aesthetic. An oversized, boxy knit worn with slim trousers is a deliberate style choice. A fitted ribbed jumper tucked into a midi skirt is another. A drapey wide-sleeve knit layered over a shirt is something else entirely.

So before you size, ask yourself: do I want this relaxed, fitted, or oversized? If you want a relaxed fit, you might size up. If you want it close to the body, stick to your measurements or size down in stretchy fabrics. I'd also always recommend checking the fabric content — a 100% wool jumper will have almost no give, while a merino-cotton blend will stretch slightly on the body.

How Different Brands Size Their Knitwear

This is where things get genuinely confusing, and honestly, it's one of the reasons I started recommending Tellar's Store Size Lookup tool to everyone I know. Sizing varies enormously between retailers. Here's what I've found from years of testing:

Cos — cuts are deliberately oversized and boxy. I always size down in their knitwear. Their size S often fits like a relaxed M. Their pieces are beautiful if you get the fit right.
Whistles — tend to cut true to size, sometimes slightly generous. Great for women who want a polished, tailored knit that doesn't swamp them.
Boden — their knitwear is brilliant for curves. Generally sized well, though their lambswool jumpers can come up slightly wider in the shoulder than expected.
M&S — their Per Una and Autograph knitwear lines size fairly consistently. A reliable middle ground, and their size guides are detailed.
Mint Velvet — sizes can vary collection to collection. I'd always check their specific product measurements, not just the label.
The White Company — luxurious knits that tend to come up small. I often go up a size, especially in their 100% cashmere styles.
Fat Face — slightly more relaxed in fit, great for weekend knitwear. Works well for athletic or broader shoulder frames as they don't cut too narrow.
Me&Em — their sizing tends to be consistent and very well-cut. One of my go-to recommendations for women who want something that simply fits well without guessing.

Two Independent Brands Worth Knowing

For something a bit more special, I always point clients toward two brilliant independent brands:

Brora — a Scottish brand producing some of the finest cashmere and merino knitwear around. Beautifully sized, with detailed fit information on each piece. Worth every penny.
Madeleine Thompson — an independent British knitwear designer whose pieces are genuinely investment-worthy. Her sizing is precise and the quality is exceptional. A real hidden gem.

My Top Tips for Buying Jumpers Online

Always read the fabric composition — it directly affects how the garment will drape and stretch on your body.
Look at model height and what size they're wearing — this gives you a much better sense of fit than the size chart alone.
Check the product measurements, not just the size guide. Look at the chest measurement and the length in particular.
If a brand doesn't publish measurements for individual pieces, that's a red flag. Contact customer service and ask.
When in doubt between two sizes, go up — a slightly oversized knit almost always looks more intentional than one that's too tight across the shoulders.

The Shoulder Seam Rule

Here's one specific thing I always check that most people overlook: the shoulder seam placement. On a properly fitted jumper (unless it's intentionally oversized), the shoulder seam should sit right at the edge of your shoulder — not sliding down your arm, not pulling inward. If the shoulder seam is off, no amount of clever styling will fix it. And unlike a skirt hem, you can't just take a knitwear shoulder in without significant alterations.

This is particularly relevant if you have broad or narrow shoulders. Many high street brands size for an average shoulder width, so if you're outside that range, it's worth going up or down a size specifically to accommodate the shoulder — and adjusting the rest of the fit with layering or tucking.

Use Tellar to Stop Guessing

The honest truth? Keeping track of your measurements and cross-referencing them across multiple brand size guides is genuinely tedious. That's exactly why I love Tellar.co.uk — it does all of that work for you. Tellar is the UK's leading free sizing tool, covering 1,500+ brands, and it matches your exact body measurements to the right size instantly. No size guides, no guessing, no returns.

Here's how it works:

Measure once — your bust, waist, and hips, or simply enter your size in a brand you already know fits you well.
Use the Store Size Lookup tool — get your precise size in any brand, whether that's COS, Whistles, Reiss, Arket, and hundreds more.
It's always free — no app downloads, no subscriptions. Just works in your browser.

And if you want to go deeper on sizing across all garment types — not just knitwear — Tellar's Ultimate Clothing Sizing Guide is genuinely the most comprehensive free resource I've found online. It covers everything from jeans to dresses to outerwear in brilliant detail.

A Note on Knitwear Sizing After Washing

One last thing — and this has caught me out more than once. Natural fibre knitwear (particularly wool, cashmere, and lambswool) can shrink or relax after washing if you're not careful. Always check the care label before you buy, and factor in that a wool jumper washed incorrectly can lose an entire size. If in doubt, go up a size if you run warm or intend to hand-wash at home.

For more styling inspiration and brand guides, head over to the Tellar Fashion Hub — it's packed with honest, unsponsored advice from stylists who actually know their stuff. No ads, no affiliate fluff, just genuinely useful content.

And while you're there, take a look at the Ultimate Guide to Jackets — if you're thinking about layering your knitwear under outerwear this season, it's an essential read.

Written by Ella Blake, Tellar Stylist