Why Are Clothing Sizes Different Across Brands?
There is no mandatory sizing standard for clothing in the US or most countries. Each brand sets its own measurements. Vanity sizing has made the gap worse over decades.
There is no mandatory sizing standard for clothing in the United States. Each brand sets its own measurements for what constitutes a size 6, a medium, or a size 32 waist, and there is no regulatory body that requires them to align. The result is that a size 12 at one brand fits identically to a size 8 at another. A Clootrack Voice of the Customer analysis of 55,287 US men's denim reviews from Q4 2022 through Q4 2025, published in December 2025, found sizing and waist-fit sentiment sitting at just 42% to 44% positive, well behind other purchase factors, confirming the inconsistency is still an active, current complaint rather than a solved problem from years past.
Why there is no standard to enforce consistency
The United States has no government-mandated sizing standard for clothing, and no regulatory body requires brands to align their measurements with each other. ASTM International publishes voluntary guidelines that some manufacturers use, but adoption is inconsistent and the guidelines are updated infrequently relative to how quickly bodies and fashion trends change. Without an enforced standard, each brand is free to define its own size 8, size 12, or medium however it chooses.
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What vanity sizing is and why it happened
Vanity sizing refers to the practice of labelling clothing with a smaller size number than the actual measurements would indicate, and it is why the same body measurement can correspond to a smaller size number today than it did decades ago. Brands adopted the practice because research showed customers felt better about purchases when the size label was smaller than they expected. The emotional response to fitting into a smaller size creates positive associations with the brand and increases purchase intent. This commercial incentive had no counterweight, there was no standard requiring brands to maintain consistent labelling, so most drifted toward smaller numbers over time.
The drift happened at different rates across different brands, which is why the variance between brands today can span multiple size numbers for the same body measurement.
Why online shopping makes it worse
When shopping in person, a customer can try on multiple sizes and find what fits. Online, a customer must rely on size charts, which vary by brand, are sometimes inaccurate, and are not standardised in format or measurement method. Nearly 70% of shoppers who returned an online clothing purchase cited size and fit as the reason, and the overall US online apparel return rate reached 23.4% in 2025, roughly $47.1 billion in returned merchandise against a $201.1 billion market, according to Coresight Research and Alvanon's May 2026 report.
Several startups have attempted to build body-measurement tools that match shoppers to their correct size across brands. None has achieved mainstream adoption, partly because the input, accurate body measurements, is difficult for consumers to self-report reliably, and partly because brand sizing varies enough that even accurate measurements cannot reliably predict fit across all contexts.
Does any standardisation exist?
The EU is closer to a standard than the US. EN 13402 provides a voluntary European sizing system based on body measurements rather than arbitrary size numbers. Adoption across European brands remains inconsistent. In the US, no equivalent voluntary standard has gained industry-wide traction, and none is currently being developed.
For the full breakdown, read the complete gotaprob analysis: Every Clothing Brand Uses Different Size Charts Making Online Shopping a Guessing Game With No Reliable Standard.
Sources
- Clootrack — US Men's Denim 2026 Outlook, Voice of the Customer analysis of 55,287 reviews Q4 2022-Q4 2025, published December 2025 — https://markets.financialcontent.com/times-online/article/gnwcq-2025-12-18-us-mens-denim-2026-outlook-fit-wins-attention-but-sizing-trust-decides-loyalty
- FashionUnited — Sizing Intelligence Is Strategic Priority, Coresight Research and Alvanon's May 2026 report on size/fit return rates — https://fashionunited.com/news/business/sizing-intelligence-is-strategic-priority-as-brands-prepare-for-ai-driven-commerce/2026063073231
Go deeper
Every clothing brand uses different size charts making online shopping a guessing game with no reliable standard