Help with choosing a size please

I am a bit confused by your sizing charts - Is the measurement given in the sizing chart a B cup or the upper bust measurement ? I realise the finished garment measurements for cup sizes are included but these all contain ease and I want to check that the finished garment will fit me across the shoulders. My upper bust is 35 inches and my full bust is 38 - ie a c cup. I am looking at the classic shirt - thank you 🙏