How ShirtMath measures
Every measurement on this site is a flat measurement, in inches, taken on a garment laid on a hard surface with the seams smoothed and nothing stretched. One standard, or the database is worthless.
Last verified: 26 August 2026
The photo scanner
The scanner reads one photo of a shirt laid flat and returns one number per measurement, in inches and centimeters. It is experimental, and it is honest about that in two specific ways.
- It never guesses. Any measurement it cannot read confidently is left blank rather than filled in.
- Its accuracy is stated, not implied. In our testing, about half of readings land within an inch of a real tape measurement. Treat scanner numbers as a guide and re-check anything that matters. Sleeve opening and bicep are the least reliable measurements.
You get the best results from a straight-on photo of the shirt laid flat on a contrasting surface, with the whole garment in frame. The measuring guide gives the same eight definitions the scanner uses.
Catalog measurements
Garment measurements in the catalog come from what the seller publishes for that garment. That is the ground truth ShirtMath works from — we do not re-measure retailers' stock, and we do not invent numbers they did not publish.
Measurements marked “estimated” are projections and are always labeled. They are never presented as tape measurements. Garments whose merchants publish no usable measurements — for example, bottoms with no waist and no inseam — are excluded from fit matching rather than being given invented numbers.
Fit comparison
ShirtMath compares each catalog garment against your reference shirt and reports the difference for each measurement, in inches. There is no black-box “fit score” presented in place of the numbers — the numbers are the product. If you want to see how far published sizes drift from one another, vanity sizing works through it with real figures.
Related
See the method in practice. Scan a shirt and watch which measurements it will and will not claim.
Scan a shirt