Size hub
38B Bra Size - UK, EU and Sister Size Conversions
Everything about the 38B bra size: international conversions, sister sizes, and how to check your fit.
Underbust
37-39 in / 94-99 cm
Bust
39.5-40.5 in / 100-103 cm
These are the body measurements that typically map to 38B. Measure to confirm because brands vary.
Last updated: July 9, 2026
US bra size
38B
- UK
- 38B
- EU
- 85B
- FR
- 100B
- AU
- 16B
Is 38B big or small?
38B combines a 38 band, which is on the larger end of this MVP band range, with B, which is a lower cup step. Cup letters are relative to band size, so fit can still vary by brand and style.
People often search "is 38B big" or "is 38B small", but the answer depends on both the 38 band and B cup step. Use the size label as a starting point, then confirm it with a real fit check.
What does 38B mean?
In 38B, the 38 is the band size: it describes the measurement around your ribcage under the bust. The B is the cup step, and cup volume changes with the band, so B on a 38 band is not the same volume as B on every other band.
For this dataset, 38B sits at a smaller cup step in this size range. Use that as context, not as a judgment about your body or shape.
How to tell if your 38B fits
- The band should stay level across your back when you move.
- Cups should hold breast tissue without spilling, gapping, or wrinkling.
- The center gore should sit close to your body if the style has wires.
- Straps should help shape the fit, not carry most of the support.
38B sister sizes explained
Sister sizes adjust the band and cup in opposite directions, which can keep the cup volume close while changing how firm the band feels. For 38B, nearby sister sizes include 36C and 40A.
Use the sister size finder when the cup feels close but the band needs a better fit, or read sister sizes explained for when the idea helps and where it stops.
Bra styles by breast shape
The same 38B can look and fit differently depending on breast shape. Round, teardrop, east-west, and other shapes suit different bra styles.
Common fit problems in 38B
Band rides up
If a 38B band rides up, compare 36C as a snugger-band sister size.
Cup gaps
If the cup has empty space, compare 38A or a shallower bra shape before changing the band.
Cup spills
If tissue spills over the edge, compare 38C or a fuller-cup style.
Band feels too tight
If the cup volume feels close but the band feels too firm, compare 40A.
Convert 38B to another system
Bra size charts for 38B
Use the chart pages when you want to compare 38B against full country size tables instead of opening one conversion at a time.
Popular 38B searches
Related sizes
Bra styles that work well for 38B
- For 38B, a steady band and wider wing can help larger-band sizes feel supported.
- Because B is relative to the 38 band, shallow or lightly lined cups may reduce extra space.
- If the cup edge gaps or cuts in, compare the shape as well as the size label.
- If the band feels right but cup space is off, compare 38C as a nearby cup step.
FAQ
Is 38B a big or small bra size?
38B depends on both the 38 band and the B cup step. Cup letters are relative to band size, so it is more useful to focus on fit than on whether a size sounds large or small.
What does 38B convert to in UK sizing?
In this sizing table, 38B converts to UK 38B. Brand charts can still differ, so check the retailer's chart before buying.
What sister size should I try from 38B?
If the band feels tight, try 40A. If the band rides up, try 36C.
What measurements usually make 38B?
38B usually maps to an underbust around 37-39 in / 94-99 cm and a bust around 39.5-40.5 in / 100-103 cm. Use these as calculator-aligned starting measurements, then confirm the fit because brands vary.
Why is my UK bra size different from my US size?
US and UK cup labels do not always move in the same sequence, especially after D. A conversion is a guide, not a replacement for trying the bra on.
How accurate is an online bra size calculator?
It can give you a sensible starting point from your measurements. Shape, style, fabric, and brand sizing still decide whether the bra actually fits.
Bras in your size
Looking for 38B? We may earn a commission if you buy through sponsored links.