How the bra size calculator converts centimeters to inches
Metric entries are divided by exactly 2.54 before sizing. The displayed result is therefore based on the same physical measurements regardless of the input unit.
inches = centimeters ÷ 2.54How the six-measurement calculator estimates UK band size
The three underbust entries are normalized from largest to smallest when they are supplied out of order, with a retake warning shown in the result. The normalized snug underbust is rounded to the nearest even UK band, while loose and tight help select a potentially firmer or roomier sister size.
UK band = nearest even snug underbustHow standing, leaning and lying bust measurements are combined
For the AFAB and not-listed profiles, leaning bust is used when the leaning-to-standing difference is 2.5 inches or less. Above 2.5 inches, the three bust values are averaged. The AMAB profile uses standing and lying twice, leaning once, then divides by five.
(2 × standing + leaning + 2 × lying) ÷ 5How effective bust difference becomes a bra cup size
The effective bust is compared with the underbust reference and mapped by cup index. UK double-letter cups are converted to the selected regional label. Standard EU results use 2.54 cm cup steps; Comexim and other EU2 results are rescaled to 2 cm steps and rounded to the nearest listed cup. A narrow boundary can produce two adjacent starting cups.
Known limits of an A Bra That Fits calculator result
The algorithm cannot infer breast root width, projection, fullness distribution, tissue density, asymmetry or a brand's pattern. The implementation was checked against representative abrathatfits.org results, but its output remains a starting point rather than a promise of fit.
Method sources: r/ABraThatFits Manual Sizing Guide and the original ABTF calculator. This independent project is not endorsed by either.