Formula Used
Average bust = standing bust + leaning bust + lying bust, divided by three.
Adjusted band = under bust + comfort gap - stretch allowance.
Cup difference = average bust - rounded band size.
Pressure index = bust volume difference divided by band size, multiplied by 100.
Example Data Table
| Under Bust | Average Bust | Band | Cup | Size |
|---|---|---|---|---|
| 42 | 49 | 40 | H | 40H |
| 46 | 53 | 44 | I | 44I |
| 50 | 58 | 48 | J | 48J |
How to Use This Calculator
Measure under the bust first. Keep the tape level. Do not pull it too tight. Then measure the fullest bust point while standing. Next, measure while leaning forward. Finally, measure while lying down. Enter all values in the form. Select your support preference. Adjust stretch allowance when fabric is very elastic. Press calculate. Review the estimated size, sister sizes, and pressure note.
Plus Size Bra Fitting Guide
Why Measurement Physics Matters
Plus size bra fitting needs more than one bust value. Breast tissue can shift with posture. Gravity changes the projected bust depth. A single standing value may miss this change. This calculator averages three bust positions. That gives a more stable estimate.
Band Support
The band carries most support. A firm band spreads force around the torso. A loose band lets straps carry too much load. That can cause shoulder marks. The calculator adjusts band size using stretch and comfort values.
Cup Volume
Cup size comes from the bust and band difference. Larger cups need enough depth and side coverage. Plus size cups may also need stronger wires, wider straps, and taller wings. Sister sizes help compare nearby options.
Comfort and Movement
Comfort is not only softness. It also depends on pressure balance. A bra should feel secure during movement. It should not dig, roll, or gap. Use the pressure index as a simple guide. Try more than one style when needed.
Best Fit Checks
The center gore should sit close to the chest. Cups should hold tissue without overflow. The band should stay level. Straps should guide, not lift everything. Recheck measurements after weight change, pregnancy, surgery, or major activity changes.
FAQs
1. Is this calculator only for plus size users?
No. It is designed with plus size fitting needs in mind, but anyone can use it.
2. Why are three bust measurements used?
They capture tissue movement across posture, giving a more balanced cup estimate.
3. What is a sister size?
A sister size changes band and cup letters while keeping similar cup volume.
4. Should the band feel tight?
It should feel secure, level, and supportive, not painful or restrictive.
5. Why does stretch allowance matter?
Elastic bands expand during wear, so allowance helps estimate real support.
6. Can this replace a fitting?
No. It gives guidance, but body shape and brand patterns still matter.
7. What if cups gap at the top?
Try a different cup shape, smaller cup, or style with more upper coverage.
8. What if the band rolls?
Try a firmer band, wider wings, or a longline style for more stability.