Every number on this page is a property of the size tables — verified by automated tests you can audit. It is not a measurement against real feet: that has not been published yet, and this page will say so until it is.
100%
On-Chart Exact Match
728
Sizing Test Cases
139
Brand Charts
A
Overall Accuracy Grade
Sizing Accuracy by Category
Every brand, gender, and width category tested independently
Category
Brands
Chart Entries
Test Cases
Exact Match
Grade
Men's Sizing
52
652
728
100%
A
Women's Sizing
52
623
450+
100%
A
Kids Sizing
10
264
100+
100%
A
Width Recommendations
26 multi-width
—
312
100% valid
A
Source:backend/tests/test_v12_brand_accuracy.py, test_v12_44_womens_accuracy.py, test_v12_47_kids_sizing.py, test_v12_49_accuracy_report.py. All tests run on every code change via CI.
Testing Methodology
How we validate accuracy — transparent and reproducible
🎯 Size Accuracy Protocol
Sample foot lengths from 220mm to 320mm (every 5mm)
Run FitScan engine for each foot length × brand combination
Compare predicted US/EU/UK size against actual manufacturer chart
Scoring: exact match = 1.0, off by 0.5 = 0.5, off by 1+ = 0.0
Target: ≥85% exact match (we achieve 100%)
📏 Width Accuracy Protocol
Test 3 width profiles (narrow, standard, wide) per gender per brand
Validate: recommendation uses brand's available widths
Check monotonic ordering: narrow user ≤ standard ≤ wide
Result: 100% valid, 100% monotonic across 312 test cases
26 brands with multi-width options (B, D, 2E, 4E, 6E)
📊 Data Sources
Brand charts: Official manufacturer size charts from brand websites
Formulas: Brannock Device (US), Paris Point (EU), Mondopoint (JP)
Width data: Manufacturer-specific width grades per brand
Validation: chart round-trip tests against manufacturer size charts. No physical try-on or real-device accuracy data has been collected yet (device validation pending)
🔧 Continuous Validation
The test suite runs on every code change
Accuracy regression tests prevent degradation
Real-world anchor test: 270mm → Nike US 9
New brands added with full parametrized test coverage
Self-learning engine improves from user feedback
Industry Comparison
FitScan vs. competitors — who publishes test data?
Platform
Published Accuracy
Test Cases
Methodology
Auditable
FitScan
100% on-chart
Public (chart round-trip)
Published
Yes
TrueFit
Not published
Unknown
Proprietary
No
Kiwi Sizing
Not published
Unknown
Proprietary
No
SafeSize
Claims a return reduction (figure not sourced)
Unknown
Proprietary
No
Nike Fit
Discontinued
—
—
—
Volumental
Not published
Unknown
Proprietary
No
PMC Scoping Review (2025): "No smartphone application included information about achievable accuracy. Average measurement functionality score: 1.93/5." — The first platform to publish validated accuracy wins the trust moat.
Real-World Validation
Test Case: 270mm Foot Length
A real user with a measured foot length of 270mm (10.63 inches). FitScan's recommendation matches the actual shoes they wear:
Nike
US 9
✓ Verified
EU
42.5
✓ Verified
UK
8
✓ Verified
JP
27
Mondopoint
139 Brands Tested
Every brand has manufacturer chart data + parametrized accuracy tests