Bra Size Calculator — Free Online Calculator with Step-by-Step Guide
Find your correct bra size using the modern 6-measurement method (underbust loose/snug/tight, bust standing/leaning/lying).
Bra Size Calculator
Results below
Enter Values
Band Size
24
Cup Size
AA
Sister Sizes
{"sisterDown":{"band":22,"cup":"A","size":"22A"},"sisterUp":{"band":26,"cup":"AA","size":"26AA"}}
Measurements Used
{"unit":"in","underbustLoose":"0","underbustSnug":"0","underbustTight":"0","bustStanding":"0","bustLeaning":"0","bustLying":"0","bustAverage":0,"bandInches":0,"difference":0}
Scenario Comparison
Continue with
Embed Code
Copy and paste this HTML snippet into any web page to embed this calculator directly.
<iframe src="http://127.0.0.1:59362/embed/everyday/bra-size-calculator?ref=embed" title="Bra Size Calculator — Free Online Calculator with Step-by-Step Guide" width="100%" style="max-width:600px; border:none; height:500px;" loading="lazy"></iframe>
Direct Link
Share this link to let others open the calculator in their browser.
24AA
Band 24 · Cup AA
22A
Smaller Band
24AA
Recommended
26AA
Larger Band
Sister sizes hold the same cup volume on different band lengths. Try the recommended size first, then experiment with sister sizes if needed.
0in
Snug Underbust
0.0in
Avg Bust
0.0in
Difference
24AA
Final Size
Your body is 3-dimensional. A single bust measurement can't capture the full picture. Breast tissue shifts — it spreads out when you lie down, projects forward when you lean, and settles naturally when you stand.
Three underbust measurements (loose, snug, tight) help determine the ideal band size that is supportive without being uncomfortable. The snug measurement is the primary reference, while loose and tight provide context for tissue compressibility.
Three bust measurements (standing, leaning, lying) together give a much more accurate estimate of cup volume than any single measurement. The average accounts for different breast shapes and tissue densities.
This is the “A Bra That Fits” (ABTF) methodology, widely regarded as the most accurate approach to bra sizing available without professional fitting.
The Formula
Modern bra sizing uses multiple bust measurements (standing, leaning, and lying) for greater accuracy, recognizing that breast tissue distributes differently in each position. The band size is the snug underbust measurement rounded to the nearest even number. The cup size is the difference between the average of the three bust measurements and the band measurement, mapped to cup letters (1 inch = A, 2 inches = B, 3 inches = C, etc.). Sister sizes provide alternative band/cup combinations that hold the same volume.
Variable Definitions
Band & Cup Size
Band is the underbust rounded to the nearest even. Cup is the difference between average bust and underbust mapped to a letter (1" = A, 2" = B, etc.). Together they form your size (e.g., 34C).
Average Bust
The arithmetic mean of the standing, leaning, and lying bust measurements. Using the average smooths out measurement variations and provides a more representative bust circumference.
Sister Size
An alternative size combination where the band changes by ±2 inches and the cup changes by ±1 step to maintain approximately the same cup volume. Useful when your recommended size is not available.
How to Use This Calculator
- 1
Select your preferred measurement unit: inches or centimeters.
- 2
Take all six measurements carefully using a soft, flexible measuring tape. Measure snug but not tight.
- 3
Enter each measurement in the corresponding input field — standing bust, leaning bust, lying bust, snug underbust, tight underbust.
- 4
View your calculated band size, cup size, full bra size, sister sizes, and a detailed measurement breakdown.
- 5
Check sister sizes — if your exact size is unavailable, these alternatives hold the same cup volume.
Modern bra sizing uses the snug underbust for band and average of 3 bust measurements for cup, plus sister sizes.
Understanding the Concept
Traditional bra fitting uses just two measurements (underbust and standing bust) with an outdated "+4" method that adds 4 inches to the band size — a practice from an era when bras were made of non-stretchy materials. Modern bras contain elastic fabrics that provide support through a snug band, not an artificially inflated one. Adding 4 inches puts most of the support on the straps instead of the band, leading to poor fit, shoulder pain, and inadequate support. This calculator follows the "A Bra That Fits" (ABTF) methodology, developed by the bra-fitting community, which uses six measurements to account for the fact that breast tissue distributes differently when standing, leaning forward at 90 degrees, and lying down. This multi-position approach gives a much more accurate starting point for finding well-fitting bras. Many people who use this method discover they have been wearing the wrong size for years — often a band that is too large and a cup that is too small. No single measurement tells the whole story, which is why the three-position bust averaging is central to this approach.
Frequently Asked Questions
Related Calculators
Reviews
No reviews yet. Be the first to share your experience with Bra Size Calculator — Free Online Calculator with Step-by-Step Guide.
Write a Review