The 38A Bra Size
Comprehensive dimensional breakdown for the 38A bra size, including tissue volume displacement, physical root profile, sister sizes, and global conversions.
Physical Measurement Breakdown
Snug ribcage baseline directly beneath breast tissue.
Taken around the fullest contour of the bust.
Approx. 256g (~0.56 lbs) per breast.
Mathematical Delta: The A cup represents a 1-inch difference between your ribcage (38") and fullest bust (39").
Sister Sizes (Identical ~269cc Volume)
If the 38A cup volume encapsulates your breast tissue without overflowing or empty space, but the band requires mechanical adjustment, these sister sizes hold the exact same volumetric capacity:
Volumetric Profile
Volumetric density index computed at ~0.95 g/cm³ human glandular/adipose baseline.
International Matrix
- UK (Standard)38A
- US Equivalent38A
- Europe (EU)85A
- Australia (AU)16A
- France (FR)100A
Verify Your Measurements
Use our precision 6-point algorithmic calculator to ensure this is your exact mathematical fit.
Open Fit CalculatorErgonomic & Structural Analysis: The 38A Profile
The 38A reflects a broader ribcage foundation paired with a modest projection depth. With a 38-inch underbust and a 1-inch overbust differential, your estimated volume of 269cc is distributed broadly across a wide chest wall.
The most common fit frustration for a 38A is underwire pinching. Traditional bra grading formulas mistakenly assume that as band sizes increase into the 38-48 range, breast tissue must project forward deeply. As a result, standard department store bras often feature cups that are too narrow and projected, resulting in empty cup tops while the underwires painfully pinch the lateral edges of your breast roots near your ribs.
Optimal Design Specs for 38A
- Wide-Root Underwires: Choose brands known for shallow cup projection and broader wire curvature.
- Comfort Underband Wings: Bands with 3 or more hooks prevent the fabric from rolling or folding beneath the bust when seated.
- Plunge or Front-Close Styles: Lower center gores eliminate pressure on the sternum while keeping the band securely seated.
The Golden Rule of Volume Conservation
Cup sizes do not represent fixed volumes. The A cup on a 38 band holds exactly 269cc. If you increase the band to 40, you must decrease the cup to maintain this exact volume (40AA). Never alter your band size without adjusting your cup letter accordingly.
Frequently Asked Questions for Size 38A
Is the 38A bra size considered big or small?↓
Cup size is entirely relative to band size. A 38A holds approximately 269cc of breast tissue volume. It holds exactly the same volume as a 36B and a 40AA.
What does a 1-inch overbust difference mean for a 38A?↓
In modern bra sizing math, every 1-inch difference between your ribcage and the fullest part of your bust equals one cup step. Measuring 38 inches underbust and 39 inches overbust creates a 1-inch delta, confirming the A cup bracket.
What are the sister sizes for a 38A?↓
The sister sizes that hold the identical 269cc volume are 40AA (if the 38 band feels too constricting) and 36B (if the band slides up your back).
Why do underwires feel wide or poke my sides in a 38A?↓
With a 38 band and A cup, your breast tissue is distributed over a broader ribcage circumference. Traditional bra cuts often assume larger bands automatically require deeper, narrow cups. Look for shallow-cup balconettes or front-close bras designed specifically for wide roots.
Why does my 38 band fold or roll up during the day?↓
A broader ribcage expands dynamically when sitting. If the band has only 2 narrow hooks, it can fold beneath the breast fold. Choosing a 38A bra with a 3-hook closure or a supportive leotard back prevents band-rolling.