Sister Size Calculator
Explore common sister-size alternatives across different band sizes. Use them as adjacent fit options, not guarantees of identical physical cup dimensions.
How sister sizes are calculated
The matrix moves the band in 2-inch steps and moves the cup position in the opposite direction within the selected sizing-system sequence. This produces nearby label combinations commonly used as sister-size comparisons.
- Current size: the entered band and cup establish the reference position.
- One step: a 2-inch smaller band is paired with the next cup position; a 2-inch larger band is paired with the previous cup position.
- Two steps: the same relationship is extended to a 4-inch band change where the cup sequence allows it.
The matrix is a sizing-system relationship, not a promise that two garments will have identical physical cup dimensions. Wire geometry, cup shape, fabric, and construction can change the fit. Read the sister-sizing explanation.
Frequently Asked Questions
Answers about sizing methods, measurements, and fit considerations.
What is a sister size?
Sister sizes are a common grading relationship intended to preserve a similar cup-capacity relationship while changing the band. Physical cup dimensions, wire geometry, and construction can still differ.
When should I sister size down?
If the band feels too loose and the cups otherwise fit, compare a smaller band with the corresponding larger cup. Check the complete fit before changing size.
Sizing References
- General bra sizing reference; sister-size relationships can vary with garment construction.