Tools
One block there is eight blocks here.
Type either side. X and Z convert. Y stays whatever height you were already standing at.
Y is not scaled. A portal at Y 70 in the Nether comes out at Y 70 in the Overworld, if you place it there.
Numbers truncate toward zero, which is what the game does with the 8:1 ratio. Why the Nether is shorter, and how not to lose the return portal, is on the dimensions page.