Estimate your bra size from underbust and bust measurements, with sister sizes — a starting point, since sizing varies by brand.
Measure snugly under the bust and loosely around the fullest part, standing upright. Sizing varies by brand — use this as a starting point and check fit.
estimated size
How to use this tool
Stand upright and measure snugly around the ribcage directly under the bust.
Measure loosely around the fullest part of the bust, keeping the tape level.
The calculator converts centimetres to inches before sizing.
If the band feels tight or loose, try a sister size — same cup volume, different band.
Formula & worked example
Underbust 32 inches and bust 36 inches: band 32, difference 4 inches → cup D, size 32D. Sister sizes are 30DD and 34C.
Limitations — read this before you rely on it
Bra sizing varies significantly by brand, country and style, and this method is an estimate — it cannot capture breast shape, fullness or personal comfort. Use it as a starting point, try sizes around it, and check fit: band level and snug, cups without gaps or spillage, straps not digging in. This tool is measurement-based and tasteful by design; it stores nothing and shows no imagery.
Frequently asked questions
Band from the underbust (rounded to the nearest even number) plus a cup letter from the difference between bust and band measurements.
Sizes with the same cup volume on a different band — for example 32D, 30DD and 34C are sisters. Go up a band and down a cup, or vice versa.
Brands cut differently and use different grading, so the same measurements can fit different labelled sizes. Always check the fit, not just the label.
Either — the calculator converts centimetres to inches (÷ 2.54) before sizing.
If the bust is below the underbust, or the difference is outside the standard range, re-measure — the tape may have slipped or been read at the wrong point.