By the ShutterAuthority.co.uk – The UK's Independent Window Shutter Guide Team · Updated May 2026 · Independent, reader-supported

How to Measure Your Windows for Shutters UK: Step-by-Step Guide

Measuring your windows accurately is the critical first step before installing interior shutters. Get this wrong, and you'll end up with gaps, misaligned panels, or shutters that won't operate smoothly. This guide walks you through the process used by professionals, so you can do it yourself and either DIY install or provide exact measurements to a made-to-measure supplier.

Why Accurate Measuring Matters

Interior shutters are custom-fitted to your window openings. Unlike curtains, they need to sit within the frame (or overlap slightly, depending on your chosen style). Even a 5mm error can cause problems—panels binding on the frame, visible light gaps, or hardware that won't clear the wall. Taking time to measure properly saves money, frustration, and return costs.

Tools You'll Need

• Metal measuring tape (5m minimum). Flexible fabric tapes can stretch; metal is more reliable.
• Digital measuring tape. These project a laser to the opposite wall and give you measurements instantly. Far easier for tall windows or if you're alone.
• Spirit level (60cm). To check if your window frame is actually square (many aren't).
• Pencil and paper to record measurements as you go.
• Calculator (your phone will do).

A basic digital measuring tape from a DIY retailer or Amazon UK costs £15–25 and saves time if you're measuring multiple windows.

Understanding the Types of Measurements

You need three sets of measurements for each window:

Width: Measured left to right, at the top, middle, and bottom of the opening.

Height: Measured top to bottom, at the left, centre, and right of the opening.

Depth: How far the frame sits out from the wall (relevant for choosing shutter frame thickness).

Take the smallest width and height measurement—this is what the shutters must fit within. If your frame is out of square (widths or heights vary by more than 10mm), you'll likely need made-to-measure shutters or shims to fit them properly.

Step-by-Step Measuring Process

Step 1: Prepare the window area

Clear the sill and window seat of any clutter. If you have existing curtains, try them open so you can access the full frame. Check that the window can open and close freely—if a frame is warped, you'll need to account for that later.

Step 2: Measure width

Starting at the top left corner of the frame, measure horizontally to the top right corner. Record this to the nearest millimetre. Repeat this at the middle height and at the bottom. Note all three figures—they should be roughly equal, but rarely are exactly.

If the measurements vary by more than 10mm, your frame is out of square (common in older UK homes). This affects how shutters will fit and operate.

Step 3: Measure height

From the top of the frame, measure down to the sill at the left side. Do the same in the middle and on the right. Again, record all three. Height variations often occur because sills settle unevenly or frames have shifted.

Step 4: Check for square

Use a spirit level placed horizontally on the sill and vertically against the left frame. If the level doesn't sit flush, your window isn't square. A spirit level that shows the angle of deviation (digital ones often do) helps, but visual confirmation is usually enough.

Step 5: Measure depth

With a metal tape, measure how far the frame sits from the wall surface on the left, right, and top. This is crucial if you plan to fit shutters within the frame versus having them cover the wall around the frame. Standard UK shutters are 50–80mm deep, depending on style.

Step 6: Note the frame material and condition

Are the frames wood, PVC, or aluminium? Are there any obstacles—radiators, handles, sill slopes? These affect installation decisions.

Step 7: Photograph the window

Take a couple of photos showing the full frame and the measurements you've written on paper. This helps made-to-measure suppliers understand your space, especially if you later need to describe sill slopes or unusual frame details.

Common Measuring Mistakes

• Measuring the glass instead of the frame. You need the inside-frame dimensions, not the visible glass area.
• Assuming all measurements are the same. Always take three heights and three widths—never assume symmetry.
• Forgetting to account for sill slope. UK window sills often slope outward for drainage. Shutters that don't account for this will sit badly.
• Ignoring obstacles. Radiators, handles, and light switches affect how shutters operate and must be measured around.
• Rounding measurements. Shutters are typically made to the exact millimetre. Don't round to the nearest 5mm.

Next Steps

Once you have accurate measurements, you have two realistic options:

Option 1: Made-to-measure shutters. Most suppliers will fabricate shutters to your exact measurements. This eliminates fitting problems and guarantees a professional finish, though it costs more upfront. Provide your measurements, photos, and frame details—specialists handle alignment.

Option 2: DIY installation with off-the-shelf shutters. Some retailers sell adjustable or modular shutters that fit a range of apertures. If your window is square and reasonably standard, this can work. However, you'll need to check fit carefully before purchasing.

For either route, having accurate, carefully recorded measurements means no guesswork, fewer returns, and shutters that look and work properly. Spend the extra 20 minutes measuring three times—it's time well invested.