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Fit technology, compared

Nearly every fit vendor starts from your body. ShirtMath starts from a garment you already own. This hub explains that split and points to the page that answers your question.

Last verified: 26 August 2026

What is the real dividing line between fit tools?

Almost every fit vendor starts with the shopper. They ask for height, weight and a couple of reference sizes, or read a photograph of a person, then estimate body measurements and pick a size letter to suit.

Two approaches start from the garment instead. Virtusize publicly describes comparing an item you already own against the item you are considering. ShirtMath measures a shirt laid flat and matches those figures against published garment measurements.

That decides what each tool can be wrong about. A body-first system can be wrong about you. A garment-first system can be wrong about the shirt, a smaller and far more checkable error.

Why does the letter on the label not settle it?

Size letters are not standardised between cuts. A ladies' Gildan G500L Medium is published at 17.5" across the chest, against 20.0" for the unisex Gildan G500 Medium. The same letter names a different garment. Vanity sizing covers why that drift is normal.

Which page answers which question?

Body measurement vs garment measurementThe two methods, and what each gets wrong. True Fit alternativeWhat True Fit documents publicly, and where ShirtMath differs. Fit Analytics alternativeProfile-driven size advice against measuring the item. Virtusize vs ShirtMathBoth work from a garment, by different routes. 3DLOOK alternativeBody scanning from photos, and why ShirtMath skips it. Bold Metrics alternativePredicted body dimensions against measured garments.

What can ShirtMath actually do today?

ShirtMath is pre-launch. Live today: photograph a shirt laid flat with a scale card, get its flat measurements, and match them against published specifications across the catalogue. Accuracy varies by point of measure: sleeve opening and bicep are the least reliable, and anything the scanner cannot read confidently is left blank rather than guessed. There is no body scanning, no shoe sizing from a photograph and no eyewear measurement. Garment-first sizing sets out the method in full.

Is a body measurement or a garment measurement more accurate?
Neither, in the abstract. A garment measurement can be checked against the item in your hands; an estimated body measurement usually cannot.
Do I need to know my size before using ShirtMath?
No. You need a shirt that already fits. The scan measures that shirt and looks for published specifications close to it.

The quickest test is a shirt you already own. Lay it flat, add a scale card, and let the scan read it.

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