I measured myself - I was 32C before pg, and am still 32 (but bigger cup). Went to mothercare today to get a nursing bra, and was measured by the lady there because I needed help with the cup. She said I was 80cm 'so 36'. I protested and questioned, but she insisted, and brought me a 36D which fitted perfectly. Totally confused, I sneaked a look at her tape measure when she was gone, and 80cm is not 36 inches - it's 32inches. So the 36 bit is not actually inches - unless it's special Mothercare inches!
I had wondered why Mothercare didn't have any bras at all in my size online, so just as well I wasn't buying online!
The Mothercare I was at only had own brand bras but I think some might stock other brands - which means I could be well confused.