To measure shutters for a bay window, work section by section: note the bay type, take three widths and three heights per section and use the smallest, check the recess depth (70mm for a full inside fit) and read each corner angle. The wrong measurement on a bay window is the most expensive mistake in shutters. Written quote after a free survey. Here's exactly how we measure bay windows on every survey within 20 miles of Stockton Heath.
Step 1: identify your bay type
Three common bay shapes, each with its own measuring trap:
- Square bay (90°). Three sections meeting at right angles — common on 1930s semis in Appleton and Grappenhall.
- Splay bay (typically 135°). The most common UK bay — Victorian and Edwardian fronts in Stockton Heath, Lymm and Knutsford.
- Curved bay. No flat sections — the frame follows a continuous arc. Shutters here need bespoke shaped panels.
Step 2: width — three readings, smallest wins
Measure each bay section at top, middle and bottom of the recess. Brickwork is never square — variations of 8–12mm are normal in a Victorian house. Always use the smallest reading. If you use the largest, the shutter won't fit; if you use the average, you'll get binding panels.
Step 3: height — three readings again
Measure left, centre and right of each section, sill to head. Old cills sag — Edwardian houses in particular. Take the shortest reading. For a tier-on-tier shutter (two independent panels stacked), note the mid-rail height too.
Step 4: recess depth — the deal-breaker
You need a minimum of 70mm recess depth to fit shutters fully inside the recess with louvres clearing the glass. Less than that and you're into face-fit territory (frame sits proud of the wall). Measure depth at the corner where the shutter hinge will sit — that's the critical point.
Step 5: bay angles (splay bays only)
A bevel gauge or angle finder app on a phone works fine. Read each internal angle — they should match within 2°. If they don't, the bay was built off-square and the shutter frame needs scribing on site. Tell your fitter on the survey, not at install. Our bay window angles guide explains the three bay shapes and how to read each corner.
Common bay measuring mistakes
- Averaging readings. Always use the smallest width and shortest height, never the average.
- Measuring the glass, not the recess. Shutters sit in the recess, so measure brick to brick.
- Ignoring handles. Window handles that stick out can stop louvres tilting; note their depth.
- Assuming matching angles. Read each corner separately; off-square bays need scribing.
The four numbers that decide your price
(1) Total width across all bay sections (2) Tallest section height (3) Number of sections (4) Material choice. Get those four to a fitter and you'll get a budget number inside 5 minutes. Anyone quoting without a site visit is guessing, bay windows always need measuring in person. See our shutter prices guide Written quote after a free survey.
Common questions
How do you measure shutters for bay windows?+
Identify the bay type, then measure each section's width at top, middle and bottom and its height at left, centre and right, using the smallest readings. Add the recess depth at the hinge corner and, on a splay bay, each internal angle.
What recess depth do bay window shutters need?+
At least 70mm for a full inside-recess fit with louvres clearing the glass. With less depth the frame is face fitted and sits proud of the wall.
Should I use the smallest or the average measurement?+
Always the smallest width and the shortest height. The largest will not fit and the average leads to binding panels.
Do I need to measure my bay before asking for a quote?+
No. Bay windows always need measuring in person, and we measure every bay on the free home survey within 20 miles of Stockton Heath.