
Length is the easy half of fit. The width letter is what decides whether a shoe hurts.
Every seller on Stride lists width per variation, because a US 9 D and a US 9 E are different SKUs with different stock. The letter refers to the girth at the ball of the foot, measured with a tape rather than guessed from length.
Measure at the end of the day, standing, with the socks you intend to wear. Compare the number against the seller size chart, not against another brand you own.
When you fall between widths, size to the wider one for boots and the narrower one for heels. Leather stretches across, never along.