knowhersize

Reviewed

38A vs 40A

40A is bigger than 38A. The cup letter is the same, but cup volume grows with the band, so 40A's cups hold more as well as having the longer band.

Side by side

38A40A
RelationshipSame cup letter, different band
UK38A40A
AU16A18A
EU85A90A
FR100A105A
Underbust38–39 in40–41 in
Bust≈ 39 in≈ 41 in
Cup volume40A holds more

On the size chart

38A is marked in ink and 40A is outlined. The yellow diagonal through 38A shows every size with the same cup volume.

38A = UK 38A · AU 16A · EU 85A · FR 100A. Sister sizes: 36B, 40AA. 38A in full →
A
B
C
D
DD
DDD
G
H
28
30
32
34
36
38
40
42
44

Questions

Is 38A or 40A bigger?

40A is bigger than 38A. The cup letter is the same, but cup volume grows with the band, so 40A's cups hold more as well as having the longer band.

Can I wear 40A if I'm a 38A?

Only if the fit check says so. Changing the band also changes the cup volume, so try both where returns are easy.

What are 38A and 40A in UK sizes?

38A is UK 38A and 40A is UK 40A. In Europe they are 85A and 90A.