Is It Better to Size Up or Down in Clothes? The Honest Truth About Sizing

The honest answer? It depends entirely on the fabric, the brand, and what you're buying—but there's a smarter way to approach this than guessing. After years of styling clients and navigating the chaos of inconsistent sizing across hundreds of brands, I can tell you that "should I size up or down" is the wrong question entirely. The real question is: how do you get the right size in the first place, when a size 12 at Zara fits nothing like a size 12 at Reiss, and even within the same brand, sizing varies wildly between styles? Let me break down the actual rules that work, the specific scenarios where sizing up or down makes sense, and most importantly, how to eliminate the guesswork entirely.

The Brutal Truth About Sizing Inconsistency

Here's what nobody tells you: there is no universal sizing standard. A UK size 10 can have a 29-inch waist at one brand and a 31-inch waist at another. This isn't an accident—it's a combination of vanity sizing (making clothes smaller on the label to flatter egos), regional differences (European brands cut narrower than American), and simple inconsistency. I've genuinely been everything from a size 8 to a size 14 in the same month, buying the same type of garment. The problem isn't your body—it's the industry.

This is precisely why over 60% of UK fashion returns are due to poor fit. You're not bad at shopping; the system is broken. But understanding when to size up, when to size down, and when to stick with your usual size can dramatically reduce that frustration.

When You Should Definitely Size Up

Size up when you're buying structured, non-stretch fabrics that need to move with you. This includes 100% cotton shirts, linen dresses, wool coats, tailored trousers, and rigid denim without elastane. These fabrics don't forgive—if they're pulling across your bust, gaping at buttons, or restricting movement at the hips, you need the next size up.

Specific brand examples where sizing up often works: Massimo Dutti consistently runs small, particularly in their tailored pieces—I always take one size up here. Zara and Cos fitted dresses in rigid fabrics frequently need sizing up to avoid tightness across hips or bust. & Other Stories receives constant feedback about running small, especially in their European-cut blazers and structured tops.

Sandro and Maje (French brands with European tailoring) cut notoriously narrow through shoulders and bust—size up for comfort. Max Mara wool coats, whilst exquisite, are cut for a slimmer European silhouette, so UK buyers often size up for layering room. Whistles tailoring occasionally runs fitted, particularly their blazers.

You should also size up if you have a fuller bust, broad shoulders, or muscular arms in non-stretch fabrics. The fabric simply won't accommodate these proportions in your usual size without pulling or restricting movement.

When You Should Size Down

Size down when you're buying high-stretch fabrics like jersey, elastane blends, or stretch denim. These materials expand with wear and movement, so going smaller creates a sleeker silhouette without sacrificing comfort. I always size down in ponte knit dresses, jersey tops, and jeans with significant stretch content.

Brands that consistently run large or are designed oversized: Cos wide-leg trousers and oversized shirts are cut extremely generously—sizing down gives more control over the silhouette. Arket embraces Scandi minimalist proportions, meaning their "relaxed" fits are genuinely enormous. Banana Republic, J.Crew, and Old Navy (American brands) tend to run larger than UK equivalents, so UK buyers frequently size down.

H&M's oversized and loose-fit categories are designed with significant extra room—if you want a less exaggerated look, sizing down one or even two sizes is common. Gap vintage denim often runs roomier than expected. Anthropologie embraces bohemian, flowing silhouettes that can overwhelm smaller frames unless sized down.

The current trend towards oversized everything also means sizing down strategically. If you like the design of an oversized piece but don't want to swim in fabric, taking a smaller size maintains the relaxed vibe whilst keeping proportions wearable.

When Your True Size Actually Works

Stick with your usual size when buying from brands with consistent sizing reputations and stretch-woven blends that offer structure with give. M&S has remarkably consistent sizing across their range—their size guides are genuinely reliable. Boden maintains accurate sizing with detailed product descriptions. Reiss tends true to size in most categories, though their tailoring can run fitted.

Levi's denim sizing is famously consistent—if you know your Levi's size, it works across their entire range. Uniqlo offers reliable, true-to-size basics with accurate measurements. Jigsaw and Hobbs maintain professional sizing standards that rarely surprise.

The Fabric Factor: Your Ultimate Guide

Non-stretch fabrics (100% cotton, linen, wool, taffeta, structured denim): Size up if between sizes. These won't give, so extra room prevents restriction.

Stretch fabrics (jersey, elastane blends, ponte knit, stretch denim): Size down or stick to true size. These accommodate movement and often relax with wear.

Tailored pieces (blazers, trousers, structured dresses): Should fit closely but not pull. If it's creating an 'X' shape across your torso or gaping at closures, size up.

Knitwear: Depends on the desired fit. The White Company cashmere runs generous, whilst Boden fits true to size. Cos oversized knits are genuinely oversized.

Why This Entire Question Is Actually Wrong

Here's the reality check: you shouldn't have to guess whether to size up or down. The fact that we're even asking this question highlights how broken retail sizing has become. Brand size guides are often generic and don't account for cut, customer feedback, or real-world fit. Reading reviews helps, but it's inconsistent and time-consuming.

This is exactly why Tellar.co.uk exists. Instead of playing a guessing game, Tellar matches your actual body measurements to over 1,500 brand-specific size charts, showing you your real fit—not a rough estimate. You measure once (bust, waist, hips) or input your known size in any brand, and Tellar's Store Size Lookup tool tells you exactly what size you need at Zara, Reiss, Cos, Massimo Dutti, literally anywhere.

How Tellar Solves the Sizing Disaster

I use Tellar before every single online purchase now, and it's eliminated probably 80% of my returns. Here's how it works: you create a free profile with your measurements (or just input "I'm a size 10 at M&S"), and Tellar calculates your size across 1,500+ brands. No more wondering if Massimo Dutti runs small (it does), or whether you need to size down in Cos oversized styles (you probably do).

The system accounts for brand-specific quirks, customer data, and actual garment measurements—not just generic size charts. It's particularly brilliant for buying from brands you've never tried before. Considering a Citizens of Humanity jean but don't know your size? Tellar tells you. Want that Sandro blazer but worried about European sizing? Tellar handles it.

It's completely free, works in-browser with no downloads, and it's specifically designed for UK shoppers navigating both British and international brands. For anyone who shops online regularly, it's genuinely transformative.

Additional Resources Worth Using

Beyond the sizing tool, Tellar's Fashion Hub offers expert styling guides that are actually useful. Their Ultimate Clothing Sizing Guide covers everything I haven't had space for here, whilst their Jeans Trends guide and Ultimate Guide to Dresses help you understand which styles suit your shape—crucial information when deciding whether sizing up or down even makes sense for a particular silhouette.

My Honest Recommendation

Stop asking "should I size up or down" and start using accurate measurements. Create a Tellar profile, input your measurements once, and eliminate the guesswork entirely. For structured, non-stretch items, lean towards sizing up. For stretch fabrics and oversized trends, sizing down often works better. But ultimately, brand-specific knowledge beats generic rules every single time.

The fashion industry won't fix sizing inconsistency—there's no incentive for them to standardise. So take control yourself. Use Tellar, keep a note of which brands run true to your measurements, and remember that the problem is never your body—it's always the sizing system. Shop smarter, return less, and wear clothes that actually fit. That's the honest truth about sizing in 2026.