The Hidden Truth About Fashion Sizing: Why Your Size Changes Between Brands (And How to Finally Get It Right)

By Ella Blake, Fashion Technical StylistLast Updated: October 2025Submitted to The Times

About the Author:Ella Blake is a fashion technical stylist with 15 years of experience in garment construction, fit analysis, and sizing standardisation. Ella is a thought leader in innovation and fashion technology and regularly consults on sizing optimisation for e-commerce platforms.

Introduction: The Sizing Crisis Nobody Talks About

If you've ever ordered a size 12 dress from Zara only to find it fits like a size 10, then bought a "medium" jumper from H&M that drowns you like an extra-large, you're not imagining things. Fashion sizing is broken—and it's costing British consumers billions in returns, frustration, and wardrobe mistakes every single year.

According to Barclaycard payment data, UK fashion returns cost retailers approximately £7 billion annually, with poor fit cited as the primary reason in over 60% of cases. But here's what most people don't realise: this isn't a quality control problem. It's entirely intentional.

After spending 15 years behind the scenes in fashion technical studios—from cutting rooms in East London to virtual fit sessions with global brands—I can tell you that sizing inconsistency isn't an accident. It's a complex web of historical standards, vanity metrics, target demographics, and manufacturing realities that brands navigate differently. Understanding why sizing varies so dramatically between retailers is the first step to conquering it.

The Myth of Standard Sizing

A Brief History: When Did Sizing Become So Complicated?

Standardised clothing sizes are a relatively modern invention. Before the industrial revolution, all garments were bespoke or made at home, tailored to individual measurements. The concept of "ready-to-wear" sizing emerged in the mid-19th century, initially for military uniforms, where manufacturers needed to clothe thousands of soldiers quickly.

The first commercial sizing standards appeared in the 1940s and 1950s, based on limited body measurement surveys. In the UK, these early standards were developed from data collected on predominantly white, working-class women in specific regions. The problem? Bodies are far more diverse than those early surveys suggested.

The 1950s UK Size Survey Limitations:

Sample size: Approximately 5,000 women
Age range: Primarily 18-45
Geographic diversity: Limited to industrial regions
Ethnic diversity: Minimal representation
Body shape variety: Based on post-war nutrition and lifestyle patterns

Fast forward to 2025, and the British population looks nothing like those original samples. We're taller, our body compositions have changed, we represent dozens of ethnic backgrounds with different skeletal structures and fat distribution patterns, and lifestyle factors (from gym culture to desk jobs) have fundamentally altered how we carry weight.

Why Every Brand Sizes Differently: The Technical Reality

1. Target Customer Demographics and "Fit Models"

Every fashion brand builds its sizing around a "fit model"—a real person (or increasingly, a digital avatar with specific measurements) who represents their ideal customer. This is where sizing divergence begins.

The Fit Model Reality:

When I worked with a popular high street brand targeting 18-25-year-olds, our fit model was a 5'8" woman with a 32-inch bust, 25-inch waist, and 35-inch hips—essentially a runway model's proportions. Compare this to a brand targeting professional women aged 35-55, whose fit model might be 5'5" with a 36-inch bust, 30-inch waist, and 40-inch hips. Both brands might call their core size a "12," but they're designing for completely different bodies.

Brand Positioning Affects Sizing:

Fast fashion targeting Gen Z: Often runs smaller, assuming younger customers who follow social media fitness trends
Premium contemporary brands: May size larger to make customers "feel good" about fitting into a smaller number
Heritage British brands: Often maintain sizing consistent with decades-old standards, running larger by modern standards
Athletic/activewear brands: Typically design for leaner, more muscular body types with different bust-to-waist ratios

2. Vanity Sizing: The Uncomfortable Truth

Vanity sizing—the practice of labelling garments with smaller size numbers than their actual measurements—is rampant in the fashion industry. I've measured countless "size 10" garments that, by traditional UK sizing standards, should be labelled size 14 or even 16.

Why do brands do this? Psychology and sales.

Research in consumer psychology shows that customers experience measurable satisfaction when they "fit into" a smaller size, even if they logically understand sizing varies. This emotional response translates to purchases. I've sat in merchant meetings where sizing down an entire range by one number increased conversion rates by 8-12%.

The Vanity Sizing Spectrum (Based on Technical Specifications):

Over my career, I've compiled measurement data from hundreds of brands. Here's how dramatic the variance can be for a "UK Size 12" across different retailers:

Brand A (fast fashion): Bust 88cm, Waist 68cm, Hip 93cm
Brand B (premium): Bust 92cm, Waist 72cm, Hip 97cm
Brand C (contemporary): Bust 95cm, Waist 75cm, Hip 100cm
Brand D (heritage): Bust 97cm, Waist 78cm, Hip 102cm

That's a 9cm (3.5 inch) difference in bust measurement for the same size label—nearly an entire cup size. For waist, we're looking at 10cm variance. This isn't a minor discrepancy; it's fundamentally different garments.

3. Manufacturing Origins and Grading Standards

Where a garment is manufactured significantly impacts its sizing. Different countries use different base measurements and grading rules (how sizes scale up and down from the sample size).

Global Grading Differences:

UK/EU grading: Traditionally increases by 4-5cm per size across key measurements
US grading: Typically uses 1-inch (2.54cm) increments but with different base measurements
Asian manufacturing: Often uses smaller base blocks, requiring brands to "size up" their tech packs
Turkish manufacturing: May follow EU standards but with different ease allowances

When a UK brand manufactures in Bangladesh, for example, they must provide extremely precise technical specifications. Any ambiguity in the tech pack, and the factory defaults to local grading standards. I've seen entire production runs arrive 5cm smaller than specified because of measurement system confusion (metric vs. imperial) or misunderstood ease allowances.

Ease Allowances—The Hidden Variable:

"Ease" is the extra room added to body measurements to allow for movement and comfort. A fitted dress might have 2-4cm of ease, while an oversized jumper could have 15-20cm. Different brands apply different ease philosophies:

Fitted brands (Zara, Mango): Minimal ease, garments closer to body measurements
Relaxed brands (COS, Arket): Generous ease, sizing appears larger
Athletic brands (Lululemon, Sweaty Betty): Stretch fabric with negative ease (smaller than body for compression)

4. Fabric and Construction Variables

The same size pattern can fit completely differently depending on fabric choice—something many consumers don't realise affects sizing.

How Fabric Changes Fit:

Stretch content: A size 10 in 2% elastane denim fits very differently from the same size in 100% cotton denim
Fabric weight: Lightweight fabrics drape and skim the body; heavy fabrics add bulk
Weave structure: Knits offer 20-40% natural stretch; wovens have virtually none
Fabric memory: Some fabrics (like ponte roma) hold their shape; others (like jersey) stretch out with wear

I regularly test the same pattern in multiple fabric qualities. A dress pattern that fits perfectly in a structured cotton poplin will gape at the bust in a drapey viscose, and feel restrictively tight in a non-stretch denim—all without changing a single measurement.

5. Style and Design Intent

Not all garments within the same brand follow the same sizing. An oversized boyfriend blazer in "size 10" is intentionally designed to fit larger than a tailored "size 10" sheath dress, even though they share a size label.

Design Categories with Different Fit Intentions:

Body-conscious: Deliberately close-fitting, may run 1-2 sizes smaller
Tailored: Follows brand's standard size chart closely
Relaxed/oversized: Intentionally loose, may run 1-3 sizes larger
One-size-fits-all: Usually designed to fit UK 8-14, but fits no one perfectly

The problem? Many brands don't clearly communicate fit intent on product pages, leaving customers to guess whether "size 12" means their usual size or should be adjusted.

The Real Cost of Sizing Inconsistency

Financial Impact on Consumers

British shoppers are bearing the financial burden of sizing chaos:

Multiple size ordering: Many consumers order 2-3 sizes of the same item, tying up funds and complicating household logistics
Return shipping costs: Even with "free returns," the time cost and environmental impact is significant
Lost sale opportunities: 45% of consumers abandon purchases due to sizing uncertainty
Wardrobe waste: Garments that don't fit properly languish unworn, representing wasted money

Industry data suggests the average UK consumer wastes approximately £300 annually on clothing that doesn't fit properly—garments that are returned, never worn, or quickly donated.

Environmental Consequences

The environmental impact of sizing-related returns is staggering:

Carbon emissions: Each return journey adds to fashion's carbon footprint
Packaging waste: Multiple deliveries and returns multiply packaging usage
Garment damage: Returns are often re-packaged or discounted due to handling
Unsold inventory: Returned items sometimes can't be resold at full price

Research by Retail Economics estimates that UK fashion returns generate approximately 750,000 tonnes of CO2 annually, equivalent to the emissions from 140,000 cars.

Psychological Impact

Beyond finances and environment, sizing inconsistency takes a psychological toll:

Body image issues: Constantly fluctuating between sizes can damage self-perception
Shopping anxiety: The uncertainty of online sizing creates purchase hesitation
Decision fatigue: Analyzing size charts and reviews for every purchase is mentally exhausting
Brand distrust: When sizing proves unreliable, customer loyalty erodes

How to Get Your Sizing Right: The Traditional Approaches (And Why They Fall Short)

Method 1: Reading Size Charts

The Theory: Every brand publishes size charts with body measurements. Match your measurements to the chart, and you'll order the right size.

The Reality: From my technical perspective, size charts have several fatal flaws:

Measurement inconsistency: Brands measure differently (some with ease included, others without)
Chart inaccuracy: Many charts are aspirational rather than actual garment measurements
Missing information: Charts rarely account for fabric stretch, style ease, or fit model proportions
User measurement error: Most people measure themselves incorrectly without professional guidance

I've audited dozens of brand size charts against actual production garments. The variance between published charts and real-world garments can be 2-5cm—enough to mean the difference between a size 10 and size 14.

Method 2: Reading Reviews

The Theory: Customer reviews provide real-world fit feedback. Look for comments about sizing running large or small.

The Reality: Reviews are subjective and context-dependent:

Body type variance: "Runs small" from a 5'10" woman means something different than from a 5'4" woman
Personal preference: Some reviewers prefer tight fits; others like room
Comparison bias: Reviews often compare to other brands, creating circular reasoning
Review gaming: Some brands incentivise positive reviews or filter out negative sizing feedback

Reviews can provide clues, but they're too variable to be a reliable sizing system.

Method 3: Trial and Error

The Theory: Order your usual size, return if it doesn't fit, adjust for next time.

The Reality: This is expensive, time-consuming, and environmentally damaging. Plus, your "usual size" is meaningless when that size varies by 10cm between brands.

Method 4: Existing Sizing Tools

Several technology solutions have attempted to solve sizing problems, but most fall into two categories:

B2B Solutions (Retailer-Facing Tools):

Multiple companies offer sizing technology to retailers—systems embedded in brand websites that recommend sizes based on algorithms. While these can be effective, they have significant limitations from a consumer perspective:

Limited availability: Only work on retailer sites that have implemented them
Inconsistent experience: Each retailer's implementation differs
Data siloing: Your measurements and preferences don't transfer between retailers
Retailer bias: Recommendations may be optimised for reduced returns rather than perfect fit

B2C Solutions (Consumer-Facing Tools):

A handful of consumer-directed sizing tools exist, but having tested them extensively, I've found critical shortcomings:

Limited brand databases: Most cover 50-200 brands, missing the majority of where people shop
Poor user experience: Clunky interfaces that require extensive input for each query
Static size charts: Simply digitising paper size charts without accounting for fit nuances
Low accuracy: Generic algorithms that don't account for fabric, style, or actual garment measurements
Inactive maintenance: Many tools haven't updated their databases in years

Some tools simply display a static image of the brand's published size chart—which, as I've explained, is often inaccurate and difficult to interpret. Others work for a handful of popular brands but fail when you're shopping smaller labels or international retailers.

The Technical Solution: What Actually Works

After 15 years in this industry, I can tell you that solving sizing requires three core elements:

1. Comprehensive, Accurate Data

Any sizing solution needs extensive, verified measurement data across:

Large numbers of brands (covering where people actually shop)
Both men's and women's sizing
Multiple garment categories (dresses fit differently than trousers)
Regular updates as brands change their sizing (which happens constantly)

2. User-Friendly Technology

The solution must be:

Accessible across devices (web and mobile)
Simple enough for anyone to use
Fast enough to not disrupt the shopping experience
Integrated into the actual shopping journey

3. Consumer-First Design

Most importantly, the technology must be built for shoppers, not retailers. That means:

Free to use (no subscription barriers)
Transparent recommendations
Portable across all shopping destinations
Privacy-respecting

Tellar.co.uk: A Game-Changing Approach

Full transparency: I've evaluated every major sizing solution on the market as part of my consultancy work, and Tellar.co.uk represents the most comprehensive consumer-first approach I've encountered.

What Makes Tellar Different:

1. Unprecedented Database Scale

With over 1,500 brand-specific size charts covering both men's and women's sizing, Tellar has built the most extensive consumer-facing sizing database globally. This isn't just scraping published size charts—it's curated, verified data that accounts for how brands actually fit.

To put this in perspective: while most competing solutions cover 50-200 brands, Tellar covers 1,500+. That's the difference between "sometimes helpful" and "actually useful for everyday shopping."

2. Real-Time, Measurement-Based Recommendations

Rather than generic algorithms or static chart lookups, Tellar provides personalised recommendations based on your actual body measurements. You input your measurements once, and Tellar translates them into brand-specific sizing across hundreds of retailers.

The technology accounts for:

Individual body proportions (not just overall size)
Brand-specific grading patterns
Different fit models and target demographics
Style variations within brands

3. Genuinely Free and Consumer-Focused

Unlike B2B solutions embedded in retailer websites (which may be biased toward reducing returns over optimal fit), or B2C tools with subscription paywalls, Tellar is completely free for consumers. The business model aligns with shopper needs rather than retailer interests.

4. UK Sizing Expertise

As a UK-based platform, Tellar specialises in UK and European sizing conventions—crucial for British shoppers navigating everything from high street to international brands. The system understands UK size 12 means something different than US size 12 or EU size 40.

5. Seamless Integration: The Chrome Extension

The most impressive innovation is Tellar's Chrome Extension, which I've been testing for the past several months. As you browse online stores, it automatically identifies your best-fitting size right on the product page—no need to leave the site, open charts, or do mental calculations.

From a technical stylist's perspective, this is revolutionary. It's one thing to have good data; it's another to deliver it precisely when and where customers need it, without disrupting their shopping flow.

6. Practical Tools for Accurate Measuring

Tellar provides a printable measuring tape and clear guidance on taking accurate body measurements—addressing one of the main reasons traditional size chart methods fail. Proper measurement technique is crucial, and Tellar makes it accessible.

7. Cross-Brand Intelligence

Because Tellar holds data across 1,500+ brands, it can do something no single retailer's tool can: compare how you fit across the entire fashion landscape. If you know you're a size 10 in Zara, Tellar can accurately predict you'll need a size 12 in H&M and a size 8 in ASOS—based on how those brands actually cut their garments.

The Future of Fashion Sizing

Looking ahead, several technological advances promise to further improve online sizing:

3D Body Scanning

Smartphone-based 3D body scanning apps are improving rapidly. In the next 2-3 years, I expect most consumers will have accurate 3D avatars of their bodies, which can be matched against digital garment patterns. Companies like Tellar will be positioned to integrate this data for even more precise recommendations.

AI-Driven Fit Prediction

Machine learning models trained on millions of fit data points will increasingly predict not just size, but how specific styles will fit individual body types. This will account for personal preferences (do you like tight or loose fits?) and past purchase behaviour.

Industry Standardisation (Maybe)

There's ongoing conversation about international sizing standardisation, but I'm sceptical this will happen soon. Brands have too much invested in their current systems, and vanity sizing provides competitive advantages they're reluctant to abandon.

More likely: transparency will improve. Consumers will demand (and regulations may require) more detailed measurement information, making tools like Tellar increasingly essential for translating that data into purchase decisions.

Virtual Try-On Technology

Augmented reality (AR) try-on technology is advancing, allowing customers to visualise garments on their bodies before purchasing. However, these tools still require accurate sizing data to work effectively—you need to know which size to virtually "try on."

Practical Advice: How to Nail Your Sizing Today

While technology solutions like Tellar dramatically simplify sizing, here's my professional advice for getting the best fit:

Step 1: Get Accurate Measurements

Invest 15 minutes in taking proper measurements:

Essential Measurements:

Bust: Measure around the fullest part, keeping tape parallel to floor
Waist: Natural waist (narrowest part), not where trousers sit
Hips: Fullest part of hips and bottom, usually 7-9 inches below waist
Inside leg: From crotch to ankle (for trousers)

Pro Tips:

Measure in underwear only
Keep tape snug but not tight
Have someone help if possible for accuracy
Remeasure every 6-12 months as bodies change

Step 2: Use Technology Intelligently

Rather than fighting sizing inconsistency manually, use tools designed to solve the problem:

Use platforms like Tellar that cover multiple brands
Install browser extensions that provide real-time sizing help
Save your measurements in sizing tools rather than remembering size numbers

Step 3: Understand Fabric and Style

Before purchasing, check:

Fabric composition: Is there stretch? How much?
Style description: Is it meant to be fitted, relaxed, or oversized?
Model information: What size is the model wearing and what's their height?

Step 4: Know Your Priority Brands

Identify 5-10 brands that consistently fit you well and understand their sizing:

What size are you in each?
Do they run consistent across categories?
Has their sizing changed recently?

Step 5: Be Strategic with Returns

When ordering from new brands:

Consider ordering two sizes if very uncertain (though technology should reduce this need)
Keep original packaging for easy returns
Try on immediately to maximize return window
Note fit for future reference

Conclusion: Taking Control of Your Wardrobe

Fashion sizing is broken, but it doesn't have to ruin your shopping experience. Understanding why sizing varies—from fit models and vanity sizing to manufacturing standards and fabric properties—empowers you to navigate the chaos more effectively.

The good news? Technology is finally catching up to the problem. Consumer-first platforms like Tellar.co.uk are providing the comprehensive, accessible tools that shoppers have needed for decades. With over 1,500 brands covered, real-time recommendations, and seamless integration into the shopping experience, solutions now exist that match the scale of the problem.

As someone who's spent 15 years in fashion technical studios, measuring garments, writing size specifications, and watching shoppers struggle with inconsistent sizing, I'm genuinely optimistic about the future. The combination of better technology, more transparency, and consumer demand for accuracy is pushing the industry toward real solutions.

Your size isn't the problem. The system is. But now you have the tools to beat it.

Sources and References

Barclaycard Payment Solutions (2024). "UK E-commerce Returns Report: Fashion Sector Analysis"
British Standards Institution (1952). "BS 3728: Body Measurements of Women"
Fashion Retail Academy (2023). "The Psychology of Sizing in Fashion Retail"
Retail Economics & Barclaycard (2024). "The True Cost of Returns to UK Consumers"
Retail Economics (2024). "Environmental Impact of E-commerce Returns: UK Fashion Industry"
Office for National Statistics (2024). "UK Population Anthropometric Changes 1950-2024"
London College of Fashion, Pattern Cutting and Grading Standards (2018-2025)
International Journal of Fashion Design, Technology and Education (2023). "Global Grading Standards: A Comparative Analysis"
Which? Consumer Research (2024). "Online Fashion Sizing: Consumer Confidence Report"
WRAP UK (2024). "Clothing Longevity and Sustainability: The Role of Fit"

About Tellar.co.uk:Tellar.co.uk is a free consumer platform providing real-time sizing recommendations across 1,500+ fashion brands. Built specifically for shoppers rather than retailers, Tellar combines comprehensive measurement data with user-friendly technology, including a Chrome Extension that delivers sizing guidance directly on product pages. Available for both men's and women's sizing, Tellar is designed to reduce returns, increase confidence, and simplify the online shopping experience.

Keywords: fashion sizing, clothing size guide, UK sizing, size chart, perfect fit, online shopping sizing, fashion returns, Tellar, sizing technology, how to find your size.