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Bra Size in Inches

Select a US Knix chart or UK Brastop method; avoid combining the source-independent band-label reference with the calculator.

Find a source-based starting bra size

Enter snug underbust and fullest bust measurements in inches. Choose one published fitting method. US — Knix and UK — Brastop are independent starting references, not equivalent regional size conversions.

Knix US matches published underbust intervals and individual cup measurement anchors; gaps and between-anchor values are not rounded into an invented cup. Brastop UK requires a whole-inch underbust because its guide does not specify rounding for fractional measurements. Both methods are fitting starting points, not guaranteed sizes.

Select a source and enter two measurements to compare its published sizing reference.

Official references: Knix traditional bra-size chart and Brastop UK measuring guide (checked 2026-10-18). Sizemapped is not affiliated with either publisher. Bra fit also depends on shape, style and construction.

Diagram showing separate bust and underbust circumference measurement positions.
Record snug underbust and fullest bust in inches, then use them as the starting inputs.

Use inches with the source you select

Record snug underbust and fullest bust in inches. Select US Knix for its 11 published underbust ranges and measured bust anchors, or UK Brastop for its whole-inch underbust and published one-to-15-inch UK cup-difference sequence.

A band printed on a bra is a size label, not a substitute for measured underbust in every method. The Brastop cup difference is calculated from measured underbust, not the rounded even band number.

A starting point, not a universal conversion

For 32-inch underbust and 37-inch fullest bust, Knix maps its band 36 and B anchor to a US 36B starting reference; Brastop maps the same tape values to UK 32DD using its own method.

Neither outcome certifies a fit or a corresponding size in the other country. Check the chosen retailer’s product sizing and comfort guidance after the lookup.

Method & references

How this guidance is checked

These sources support the measurement method and help check real-world variation. They are not presented as one universal brand-size table.

  • Bra Fit Calculator — Wacoal. Bra measurement cross-check using underbust and fullest-bust measurements and brand-specific fitting logic.

Related sizing tasks

How to Measure Bra SizeBra Size Chart

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