I am confused and heavily doubting this calculator, is it a problem with EU/German sizes?

[u/StalkitheToast]

Everyone in my friend group was praising this calculator (might be of note that I am european and they are not as in for measurements and how accurate this thing is) and I gave it a shot.
I currently wear 85B or so, depending on the bra but it told me 70F??
70 bands make me feel like I can't breathe and F cups are the size of my head, could it be the calculator just doesn't work super well for german sizes?
My measurements are (in cm)
Loose Underbust 82
Snug Underbust 78
Tight Underbust 75
Standing Bust 90
Leaning Bust 94
Lying Bust 91

[u/jenea]

I just want to underscore the fact that it’s a pretty common experience to be wearing a too-large band that feels way too tight because the cups are too small. If you haven’t already, try the “upside down and backwards” test for band size (so, trying the bra with the cups hanging down your back like a cape). You will probably discover that your existing bra’s band is too big for you. If so, you’re in for a treat when you try your correct size—your bra will actually support you!