Bra Size Measurement Guide
Why Measurement Matters
A bra size calculator turns body measurements into a practical starting size. It is not a final fitting verdict. Bodies are not fixed cylinders. Fabric also stretches, cups have different shapes, and each style sits differently on the rib cage. This tool uses simple measurement physics. It compares two circumferences. The underbust gives a band estimate. The bust average gives a cup estimate.
Measurement Options
The calculator supports inches and centimeters. It accepts standing, leaning, and lying bust readings. When several bust readings are entered, it averages them. That helps reduce posture error. It also gives sister sizes. Sister sizes keep similar cup volume while changing band length. A smaller band usually needs a larger cup letter. A larger band usually needs a smaller cup letter.
Band Logic
The Maidenform style option follows a classic U.S. fitting approach. It rounds the underbust first. Then it adds four inches for even values or five inches for odd values. This creates an even band size. The modern snug option rounds the rib measurement to the nearest even band. Some shoppers prefer this for firm support. The comfort setting can move the band down or up one step.
Cup Logic
Cup size comes from the difference between bust and band. A one inch difference suggests A. Two inches suggest B. Three inches suggest C. The sequence continues through larger cup labels. The result should be tested with real fit checks. The center panel should sit close. The band should stay level. The cups should not dig, gape, or overflow.
Physics and Comfort
The physics section is useful because sizing is about force and shape. A band works like a flexible ring. It must stretch enough to stay in place, yet not create painful pressure. Straps should help position the garment, not carry all support. The calculator gives notes based on stretch allowance and preference.
Buying Guidance
Use the answer as a buying guide. Try the suggested size first. Then compare sister sizes when the band feels tight or loose. Change cup letters when cup space is the issue. Recheck measurements after weight changes, pregnancy, workouts, or new garments. Measure over an unpadded bra for better consistency. Save each result as a CSV or simple report for later comparison. Keep useful notes between purchases.