What size shower curtain rod do I need?

Measure wall-to-wall at the height you plan to mount, then pick a rod whose adjustment range comfortably brackets that number. Most standard alcove tubs fall in the 54–60 inch range, which is why 50–72 inch adjustable rods dominate this category. For wider walk-ins or room dividers, look at extra-long 80-inch-plus tension rods.