Monsoon dress size

[Quercus30]

I've seen a monsoon dress second hand that I'd like. It's a size 6. I would normally buy a size 6 in trousers and skirts and on the rare occassion I buy a dress for work from m and s, I'd go for a size 6. My bust is 32B ish. What are their sizes like? It's a shoulder less evening dress and I have never bought anything like this before. TIA.

I always get a 12 from monsoon and they always fit well. I'm a 12 in M&S too soo it seems to be consistent across the brands