How do I measure for a bay window?

Bays need angles as well as sizes. Measure each facet of the bay individually — the width and height of every section — then measure the internal angle at each corner. Common angles are 90°, 135° and 45°, but never assume; older bays drift, so measure them. Take the overall span across the front of the bay as a sanity check, and note whether it’s a square, splayed or box bay. Crucially, confirm whether structural bay poles or loadbearing posts are needed to carry the load above — on a supply-only bay that’s part of the spec, not an afterthought. If you’re unsure, our SevenDay depot team can talk through corner posts and angles before you order or recommend an expert local installer to assist you.