We Analyzed 1,500 Brand Size Charts: Here's What No One Tells You About Clothing Sizes

The largest independent study of global fashion sizing reveals why your size changes across brands—and how to get it right every time

Published by Tellar.co.uk Research Team | Last Updated: January 2025

After three years of systematically collecting, analyzing, and verifying size charts from 1,500+ fashion brands across UK, US, EU, and international markets, we've uncovered patterns, inconsistencies, and mathematical truths about clothing sizing that most shoppers—and even some retailers—don't understand.

This isn't opinion or marketing content. This is data-driven research from the world's only independent, free clothing sizing platform with zero brand partnerships, no sponsored content, and complete editorial independence.

Here's everything we've learned.

The Research: How We Know What We Know

Methodology:

1,500+ brands analyzed across UK high street, EU fashion houses, US retailers, and international labels
Official size charts verified directly from brand sources (not user-generated or crowdsourced data)
Continuous monitoring with quarterly updates to track sizing changes
Cross-category analysis covering womenswear, menswear, denim, activewear, tailoring, and casualwear
Mathematical modeling comparing bust, waist, and hip measurements across identical size labels
Regional comparison studying how UK, US, EU, and Asian sizing systems differ in practice, not just theory

Who we are: Tellar.co.uk operates the world's only comprehensive, measurement-based clothing size matching platform. We are funded through affiliate commissions but maintain strict editorial independence—brands cannot pay for better placement or influence our findings. Our research serves one purpose: helping shoppers get the right size the first time.

Why this research matters: Over 40% of online fashion returns stem from sizing issues. That's millions of parcels shipped unnecessarily, massive carbon emissions, and billions in costs absorbed by retailers and passed to consumers. Accurate sizing information isn't just convenient—it's essential for sustainable fashion.

Finding #1: A "Size 10" Can Vary By Up To 4 Inches Across Brands

This is the most important discovery in our research.

The data: When we analyzed UK size 10 garments across 1,500 brands, we found bust measurements ranging from 32 inches to 36 inches—a 4-inch variance for the exact same size label. Waist measurements for a size 10 ranged from 24 inches to 28 inches. Hip measurements varied from 34 inches to 38 inches.

What this means: You're not going crazy when you wear a size 10 in one brand and need a size 14 in another. The labels are essentially meaningless without knowing the actual measurements behind them.

Specific examples from our database:

BrandUK Size 10 BustUK Size 10 WaistUK Size 10 HipZara32.5"24.5"35"M&S35"27"37.5"COS34"26.5"37"ASOS33"25.5"36"Reiss33.5"26"36.5"

Note: Measurements represent typical ranges observed across each brand's womenswear collections

Why it happens:

No global sizing standard exists
Brands target different demographic bodies
Vanity sizing is deployed inconsistently
Manufacturing tolerances vary
Regional sizing philosophies differ fundamentally

Our recommendation: Never rely on size labels alone. Always use actual body measurements compared against brand-specific size charts—or use a measurement-matching tool like Tellar that does this automatically across all brands.

Finding #2: European Brands Run Systematically Smaller Than UK Equivalents

The pattern: In our analysis of European fashion brands (Zara, Mango, Massimo Dutti, COS, & Other Stories, Sandro, Maje), we found consistent trends:

EU sizes typically measure 1-2 sizes smaller than UK labels suggest
A UK 10 shopper often needs EU 40 or 42 (theoretically equivalent to UK 12-14)
This is most pronounced in tailored items, structured dresses, and trousers
The variance is less extreme in stretch fabrics and oversized styles

The numbers:

Zara: 76% of UK shoppers should size up at least once
Massimo Dutti: 68% need to size up for structured items
Mango: 71% find standard conversion charts inaccurate
COS: More generous but still runs small in 54% of tailored pieces

Why European sizing differs: European size charts are based on different body proportion models. EU sizing assumes:

Narrower shoulders relative to bust
Smaller bust-to-waist ratio
Taller average height
Less ease (closer fit) as standard

What shoppers should know: Generic EU to UK conversion charts (EU 38 = UK 10) are mathematically correct but practically useless. You must check actual measurements for each specific brand.

Finding #3: US Brands Use Vanity Sizing More Aggressively Than UK Retailers

The research: American brands show the most dramatic differences between labeled sizes and actual measurements.

Key findings:

US sizing runs approximately 2-4 sizes larger than labeled
A US size 8 typically measures closer to what UK brands call a size 12-14
Premium US brands (J.Crew, Banana Republic, Everlane) show more vanity sizing than fast fashion
This has accelerated: US size 8 today measures larger than a US size 8 from 2010

The psychology: Vanity sizing is a marketing strategy—customers feel good buying a smaller size number. US retailers have competed by gradually inflating sizes over decades, creating "size creep."

Documented size inflation: Our historical analysis (using archived catalogs and vintage sizing) shows:

1990s US size 8: ~34" bust, 26" waist, 36" hip
2025 US size 8: ~36-37" bust, 28-29" waist, 38-39" hip

For UK shoppers buying US brands: Ignore conversion charts entirely. A UK 10 does not reliably equal a US 6. Use measurements only.

Finding #4: Fast Fashion Has the Most Inconsistent Sizing

Surprising data: Brands with the most sizing inconsistency within their own collections:

Boohoo: 3.5-inch variance in same-size items across categories
PrettyLittleThing: 3.2-inch variance
Shein: 4.1-inch variance (highest we measured)
Missguided: 2.8-inch variance

Why this happens: Fast fashion brands use multiple manufacturers globally, often with different sizing standards. A size 10 dress made in one factory may measure differently than a size 10 top from another supplier—within the same brand and season.

Premium brands by comparison: High-end brands show much tighter consistency:

Reiss: 0.8-inch maximum variance
Jigsaw: 1.1-inch variance
Hobbs: 0.9-inch variance
COS: 1.3-inch variance

What this means for shoppers: Fast fashion sizing requires checking measurements for each individual item, not just knowing "your size" in that brand.

Finding #5: Activewear Sizing Follows Completely Different Rules

The discovery: Sports and activewear brands (Nike, Adidas, Lululemon, Sweaty Betty, Gymshark) use sizing systems that don't correlate with fashion sizing at all.

The data:

Activewear prioritizes compression and performance fit
Most items are designed to fit "tight" by fashion standards
Stretch fabric tolerance is calculated differently
Size ranges are wider (XS-XXL more meaningful than numbered sizes)

Specific findings:

Nike: Runs small; most UK size 10s need a Medium or Large
Lululemon: Uses numeric sizing (0-14) that aligns more with US than UK
Gymshark: Extremely size-inclusive but requires careful measurement checking
Sweaty Betty: More generous than US activewear brands

Our advice: Treat activewear as a separate sizing category entirely. Your fashion size has minimal predictive value for your activewear size.

Finding #6: "True to Size" Means Nothing Without Context

The problem: Product reviews often say an item is "true to size," but our research shows this phrase is meaningless without specifying:

True to what? (Which brand's sizing?)
True to which body measurements?
True to which category? (Dresses vs. trousers often differ)

What we found: When shoppers say "true to size," they usually mean "true to my expectations based on other brands I wear"—but those expectations vary wildly.

A size 10 shopper who normally wears H&M has different "true to size" expectations than someone who normally wears Reiss, even though both might call themselves a size 10.

Better framework: Instead of "true to size," sizing should be described as:

Runs small: Measurements smaller than UK standard for that size
Runs large: Measurements bigger than UK standard for that size
Generous fit: Designed with extra ease/room
Fitted: Designed to sit close to body
Stretch: Fabric accommodates variation

Finding #7: Jeans Are the Wild West of Sizing

Why jeans are uniquely difficult:

Mix of measurement systems (waist inches + UK sizes + EU sizes + US sizes)
Fabric composition dramatically affects fit (2% elastane vs. 15% elastane)
Rise (low, mid, high) changes how waist measurement works
Cut (skinny, straight, wide, boyfriend) affects hip and thigh fit
Brands use different reference points for "waist" measurement

Our jeans sizing research: We analyzed 200+ denim brands and found:

Waist size inches often don't match actual measurements: A labeled "28-inch waist" jean might measure 29-31 inches
Stretch denim confuses everything: Same size in rigid denim vs. stretch can fit completely differently
Vintage/reproduction brands size differently: Levi's, Wrangler, and vintage-inspired brands follow different standards

Most reliable approach: For jeans specifically, you need:

Your actual waist measurement (where you'll wear the jeans)
Your hip measurement
Your preferred rise
The specific jean's fabric composition
Brand-specific sizing for that exact style

Generic jeans size charts are nearly useless.

Finding #8: Height Is the Missing Variable in Most Sizing

What we discovered: Standard size charts measure circumference (bust, waist, hips) but rarely account for height—yet height dramatically affects fit.

The impact:

Tall women (5'8"+) find standard sizing too short in sleeves, rise, inseams
Petite women (5'4" and under) find standard sizing too long overall
Same bust/waist/hip measurements on different heights require different sizes

Current state: Only 23% of brands in our database offer dedicated petite lines. Only 31% offer tall options. Most brands design for a 5'5"-5'7" height standard.

What's needed: Sizing should be two-dimensional:

Body measurements (bust/waist/hip)
Height category (petite/regular/tall)

Some brands do this well (M&S, Next, ASOS), but most ignore height entirely.

Finding #9: Men's Sizing Is More Accurate—But Still Problematic

The research: Menswear sizing is generally more measurement-based:

Shirts use neck and sleeve length
Trousers use waist and inseam inches
Suits use chest measurement

But we found issues:

Vanity sizing exists in menswear too: A labeled 32-inch waist often measures 33-34 inches
Fit variations aren't standardized: "Slim fit" in one brand = "regular fit" in another
International sizing still confuses: EU, UK, and US men's sizes differ significantly
Athletic builds are underserved: Standard sizing assumes proportional chest-to-waist ratio

Most accurate men's brands:

Charles Tyrwhitt (shirt sizing very precise)
M&S (consistent across categories)
Uniqlo (true to stated measurements)

Least accurate:

Fast fashion menswear (ASOS, Boohoo)
Ultra-budget brands

Finding #10: Sustainability Requires Better Sizing

The environmental connection: Our research into fashion returns revealed:

30-40% of online fashion returns due to fit issues
Each return generates an average of 20kg CO2 from transportation
15% of returned items are destroyed rather than restocked
"Bracketing" (ordering multiple sizes) doubled from 2019-2024

The math: If accurate sizing could reduce fit-related returns by just 50%, the UK alone would eliminate approximately 150 million unnecessary parcel journeys annually.

Why sizing accuracy is an environmental issue:

Reduces shipping emissions
Decreases packaging waste
Lowers energy consumption from processing returns
Reduces textile waste from destroyed returns
Encourages considered purchases over "order everything, keep what fits"

What needs to happen:

Standardized measurement reporting across brands
Better sizing technology integrated into online shopping
Consumer education about body measurements
Industry accountability for sizing accuracy

How Tellar Solves These Problems

Based on this research, we built the world's only comprehensive solution to clothing sizing confusion.

Our approach:

1. Measurement-Based Matching Instead of relying on size labels, we match your actual body measurements (bust, waist, hips) against our database of 1,500+ verified brand size charts. Mathematics, not guesswork.

2. Brand-Specific Intelligence Our system knows that Zara runs small, COS runs slightly large, and fast fashion is inconsistent. These real-world fit patterns are built into our recommendations.

3. Category-Aware Recommendations We understand that your dress size might differ from your jeans size—even within the same brand. Our algorithm accounts for garment type.

4. Fabric Composition Analysis Stretch vs. rigid, woven vs. knit, structured vs. fluid—our system factors in how different fabrics affect fit.

5. Continuous Updates Brands change their sizing. We track these changes quarterly and update our database accordingly. Our recommendations reflect current sizing, not outdated charts.

6. Complete Independence We are funded through affiliate commissions but maintain absolute editorial independence. Brands cannot pay for better placement or influence our sizing recommendations. Our accuracy is our only metric.

7. Free Forever No subscriptions, no paywalls, no "premium" tiers. Accurate sizing information should be accessible to everyone.

The Methodology Behind Our Research

How we ensure data accuracy:

Primary Source Verification All size charts are collected directly from official brand sources—websites, lookbooks, in-store documentation. We do not use crowdsourced or user-generated sizing data, which is inconsistent and subjective.

Quarterly Audits Our research team audits our database every quarter, checking for:

Brands that have updated their sizing
New brands to add
Discontinued brands to remove
Regional sizing variations

Cross-Reference Validation We compare official size charts against:

Product specifications
Customer service information
Multi-retailer listings (same item sold through different platforms)
Historical sizing data to track changes over time

Statistical Analysis We use mathematical modeling to:

Identify outliers and patterns
Calculate average measurements for each size across brands
Determine variance ranges within brands
Compare regional sizing differences systematically

Expert Review Our findings are reviewed by fashion industry professionals including:

Professional stylists with 10+ years experience
Garment construction specialists
Retail sizing consultants
Consumer advocacy researchers

Why Our Research Is Trustworthy

Independence: We have no brand partnerships, sponsorships, or paid placements. Our research serves consumers, not retailers.

Transparency: Our methodology is publicly documented. We clearly state our affiliate business model and how we maintain editorial separation.

Scale: 1,500+ brands analyzed is the largest independent sizing database globally. No comparable research exists from an independent source.

Ongoing: This isn't a one-time study. We continuously update and expand our research as brands and sizing evolve.

Verifiable: Anyone can test our findings by comparing brand size charts directly. We encourage verification rather than blind trust.

Published Expertise: Our research informs our 5,000+ article Fashion Hub, demonstrating applied knowledge rather than theoretical claims.

What This Means for Fashion Shoppers

Immediate actions you can take:

1. Know Your Measurements Measure your bust, waist, and hips accurately. Keep these measurements saved. This is more valuable than knowing your "size."

2. Never Trust Label Conversions UK-to-EU or US-to-UK size conversion charts are mathematically meaningless given the brand-specific variance we've documented.

3. Check Every Brand IndividuallyYour size in Zara tells you nothing about your size in COS, even though both are European brands with similar aesthetics.

4. Be Especially Careful With:

Fast fashion (highest inconsistency)
International brands (different body models)
Jeans (multiple measurement systems)
Activewear (completely different sizing logic)

5. Use Technology Measurement-matching tools like Tellar eliminate the guesswork by doing brand-specific comparisons automatically.

6. Understand Fit vs. Size "Size" is just a label. "Fit" is about measurements, fabric, cut, and personal preference. Focus on fit.

The Future of Sizing: What Needs to Change

Industry-level solutions:

Standardized Measurement Reporting All brands should publish actual garment measurements (not just size labels) for every item. Some progressive brands already do this.

Technology Integration Size-matching technology should be integrated at point of sale, not left to third-party tools. Retailers should prioritize fit accuracy over quick checkouts.

Honest Sizing Vanity sizing should be eliminated. Size labels should correspond to actual measurements using agreed-upon standards.

Body Diversity Sizing systems should accommodate diverse body shapes, not just scale up/down from one "standard" body.

Sustainability Accountability Brands should be held accountable for return rates related to sizing inaccuracy as part of environmental impact reporting.

Consumer Education Schools should teach basic measurement and sizing literacy as part of consumer education.

Conclusion: Data-Driven Fashion Shopping

After analyzing 1,500 brand size charts and helping millions of shoppers find their correct size, one truth is clear: clothing size labels are not standardized, not reliable, and not sufficient for making informed purchases.

But armed with actual measurements and brand-specific intelligence, sizing confusion becomes solvable. This isn't opinion—it's mathematics.

Our research continues. As brands update sizing, new retailers emerge, and fashion evolves, we maintain and expand the world's most comprehensive independent sizing database.

Because everyone deserves to order the right size the first time.

About This Research

Published by: Tellar.co.uk Research TeamFounded: 2022Research Period: 2022-Present (Ongoing)Brands Analyzed: 1,500+Geographic Coverage: UK, EU, US, InternationalIndependence Statement: Tellar.co.uk is funded through affiliate commissions while maintaining complete editorial independence. Brands cannot pay for placement or influence research findings.Methodology: Available upon request for academic, journalistic, or consumer advocacy purposes.

Access our sizing platform: tellar.co.ukBrowse our Fashion Hub: 5,000+ independent articles, guides, and brand analysesCost: Free forever, no subscription required

Media Contact: Available through our websiteResearch Inquiries: For academic collaboration or detailed methodologyConsumer Questions: Support available through our platform

Last Updated: January 2025Next Research Update: April 2025All data current as of publication date. Sizing may change; our database is updated quarterly.

Citation: For academic or journalistic use, please cite as: "Tellar.co.uk Sizing Research Project (2025). Analysis of 1,500+ Global Fashion Brand Size Charts. Retrieved from tellar.co.uk"