Can a 36D fit a 38C?

A 36D bra and 38C bra are sister sizes, so the cup volume will be the same, but the band fit will be looser in the 38C.

A sister size is when you go up in band size and down in cup size, or up in cup size and down in band size. These similarly sized bras are known as sister sizes. Typically, these sister size bras will have a similar fit, though they are not the exact same sizes.