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Making size feel
less like a gamble
As a Senior Product Designer at ASOS, I led a discovery into one of the hardest parts of buying fashion online: deciding whether something will fit before you can try it on.
Rather than starting with a feature, I set out to understand the decision itself: what gives customers confidence, what creates doubt, and what they do when the information isn’t enough.
- Company
- ASOS
- Focus
- UX research & discovery
- Theme
- Size, fit & purchase confidence
- When
- 2024–2025
At a glance
The problem
Customers must judge fit through a screen, often with conflicting signals.
My approach
Interviews and a survey to understand sizing behaviour before deciding what to build.
The outcome
A set of opportunity areas that shaped ASOS’s fit strategy work.
01: The problem
You can’t try it on through a screen
Choosing a size looks like a simple task, but behind it customers are predicting how a garment will fit their body from imagery, size charts, past experience and any other evidence they can find. When those signals don’t add up, uncertainty becomes part of shopping.
The research question
“What gives customers enough confidence to choose a size and buy, and what happens when that confidence breaks down?”
02: Approach
Don’t start with the size guide
It would have been easy to frame this around improving one sizing feature. Instead, I stepped back to understand how people build confidence when they can’t physically try a product.
01 · Understand
How do people choose?
The information, experience and personal rules behind a size decision.
02 · Observe
Where does doubt appear?
Moments of hesitation, reassurance-seeking and drop-off.
03 · Uncover
What sits behind it?
The needs beneath the feature requests.
04 · Define
Where could ASOS help?
Opportunity areas the product team could validate.
03: Research
Two studies, one question
Moderated interviews showed how customers behave when choosing a size on their phones. A survey tested how widely those patterns held, and how they differ between womenswear and menswear.
10+
Moderated interviews
With shoppers across a range of ages, on their own phones
100+
Survey respondents
UK shoppers, via an online research panel
Most
Hit inconsistent sizing
Between brands, especially jeans, tops and dresses
Most
Trust other shoppers
For size advice, more than retailer recommendations
The prompt that grounded every interview
“Talk me through the last time you wanted something but weren’t sure which size to order.”
04: What we found
Confidence is built from more than measurements
01
People trust people
Most interviewees preferred customer photos and reviews with fit details over any other tool, and these consistently came out as the most trusted signal in the survey too.
02
Size guides miss the mark
Many customers didn’t know their own measurements, and found detailed charts off-putting. Most relied on model height and size worn instead.
03
Familiarity is a shortcut
Customers valued brands they knew, because consistent sizing meant fewer returns. Inconsistent sizing between brands was one of the most common challenges raised.
04
Confidence isn’t equal
Women felt noticeably less confident choosing a size than men did. Jeans were the hardest category for both.
05: The shift
The problem wasn’t size. It was confidence.
Customers weren’t looking for more sizing information. They were gathering enough evidence to trust the choice they were about to make.
Research principle
“Don’t just opt for more information. Understand what gives someone enough evidence to make a confident decision.”
06: Opportunity areas
Six places ASOS could build confidence
01
Personal size profiles
Store measurements and sizes in favourite brands, so customers don’t start from scratch each time.
02
Size-specific reviews
Let customers filter reviews by body type, height and size bought.
03
More diverse models
Show varied body types and sizes, especially for swimwear, dresses and outerwear.
04
Simpler, more precise guides
Core product measurements, with clear help on how to measure yourself.
05
Fit tools people can find
Improve the coverage and discoverability of sizing and fit tools.
06
Help when it’s out of stock
Suggest similar items available in the customer’s size.
07: Outcome
Where the discovery went
This phase deliberately stopped before solution design. Its output was understanding, which went on to shape strategy, ideation and early concepts.
Strategy
Fit strategy
User stories from the insights informed the strategic focus of the wider fit team.
Ideation
How might we…
Ideation sessions with the wider product and fit team stakeholders.
Concept
Fit in reviews
Fit ratings in the review form and fit highlights on the product page.
08: Reflections
What the project taught me
Next
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John Lewis & Partners
A home for reviews, where customers already are
A My Reviews area in My Account that made submitting a review easy to find, now the second-largest source of review submissions.