How to Measure for Perfect Fit Shutters: Step-by-Step

Getting the measurement right is the single most important part of buying perfect fit shutters. The clip-frame system that makes them so practical — no drilling, no damage, fits directly into the UPVC glazing bead — also means the dimensions need to be accurate. Unlike a conventionally mounted blind where a centimetre of extra width just means the blind overhangs the frame slightly, a perfect fit product has to match the internal frame dimensions precisely to clip in correctly.

The good news is that measuring is straightforward once you understand what you're actually measuring. This guide walks through the process step by step.

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What You're Measuring — and Why It's Different

Most window measurement guides tell you to measure the width and drop of the window. For perfect fit shutters, that instruction isn't precise enough.

You are not measuring the external width of the window frame. You are not measuring the window reveal. You are measuring the internal glazed area — the clear opening between the inner edges of the glazing bead on all four sides.

The glazing bead is the narrow channel that runs around the inside of a UPVC frame, holding the sealed glass unit in place. The perfect fit clip frame seats into this channel. The dimension you need is the measurement from the inner edge of the bead on one side to the inner edge on the opposite side — width and height.

What You'll Need

A steel tape measure. Not a fabric tape, not a laser measure for this purpose — a rigid steel tape that holds straight across the window without sagging. A pencil and paper, or your phone for noting measurements. That's it.

Step One: Measure the Width

Open the window fully so you have clear access to the frame. Place the tape measure at the inner edge of the glazing bead on the left side and extend it to the inner edge on the right side.

Take this measurement at three heights: near the top of the glazed area, at the midpoint, and near the bottom. Record all three numbers.

Use the smallest of the three measurements as your width figure. Windows that appear perfectly square often aren't — slight frame settlement or manufacturing variation means the dimensions differ by a few millimetres across the height. Using the smallest measurement ensures the clip frame will seat correctly at the tightest point.

Step Two: Measure the Drop

Measure the internal height of the window from the inner edge of the glazing bead at the top to the inner edge at the bottom.

Take this measurement at three positions: left side, centre, and right side. Record all three. Again, use the smallest measurement as your drop figure.

For tilt-and-turn windows, measure the opening sash only — from the top of the lower sash frame to the bottom of the sash. Do not include the fixed surrounding frame in your measurement. The perfect fit shutter clips to the opening sash, not the full window surround.

Step Three: Check the Bead Channel is Clear

Run your finger or a cloth along the glazing bead channel on all four sides. Paint overspray from previous decoration, dust build-up, or silicone residue can partially obstruct the channel and prevent the clips from seating fully. Clear any obstruction before the shutters arrive — it's easier to do now than when you're mid-installation.

Step Four: Note Any Obstructions

Look for anything within the frame that might interfere with the shutter panel — existing trickle vents, handle positions on tilt-and-turn windows, or any hardware mounted to the frame. Note their position and distance from each edge. Your supplier may need this information if any obstruction falls within the panel area.

Step Five: Measure Bay Windows Separately

If you have a bay window, treat each section as an individual window. Measure each pane separately — width and drop — and record them independently.

Even when bay sections look identical from the front, the internal dimensions often differ by several millimetres. Ordering all panels to the same dimension based on a single measurement is the most common bay window mistake. You will typically need three separate panels for a standard three-section bay: a wider centre panel and two narrower returns. Measure all three individually.

Ordering: One Important Clarification

When you submit your measurements to the supplier, confirm which dimension convention they use. Some systems are ordered to the exact internal glazed area measurement — the number you've recorded. Others quote a nominal blind size that differs slightly because the outer frame's own dimensions are factored in at the manufacturing stage.

These are not the same number, and ordering to the wrong convention is the most common cause of sizing errors. A quick confirmation before placing the order takes thirty seconds and avoids a return.

Measure twice, order once. For perfect fit shutters — and for perfect fit blinds of any style — the measurement is the step that determines whether the product installs perfectly or doesn't install at all. Get the internal glazed area dimensions right, and everything else follows naturally.