How to measure shutter depth: a homeowner’s guide
TL;DR:
- Accurate measurement of shutter depth is essential to ensure shutters open and close properly within the recess.
- Homeowners should measure width, height, and depth in multiple places, always recording the smallest readings for an exact fit.
Shutter depth is defined as the distance from the front edge of your window frame to the nearest obstruction inside the recess, such as a handle, crank, or sill board. Getting this measurement right determines whether your shutters will open, close, and tilt freely. Inside mount shutters achieve a clean, fitted look but require adequate recess depth and a square window opening. Knowing how to measure shutter depth accurately before you order is the single step that separates a flawless installation from a costly refit. Shutterworld’s bespoke shutter service is built on this principle: precise measurements first, perfect fit guaranteed.
What tools do you need before measuring shutter depth?
The right tools make the difference between a confident measurement and an expensive guess. Gather these before you start:
- Steel tape measure (3 metres minimum, with a locking mechanism)
- Pencil and notepad or a printed measurement sheet
- Spirit level to check whether your window frame is plumb and level
- Step stool if your windows are above head height
- Camera or smartphone to photograph the recess and any obstructions
Preparation matters as much as the tools themselves. Remove all curtains, blinds, and any existing window coverings before you begin. Clear the windowsill of ornaments, plants, and anything else that might obstruct your tape measure. Check that you can see the full depth of the recess from front to back without anything blocking your line of sight.
Pro Tip: Run your hand along the inside of the recess before measuring. You will often feel protruding screws, uneven plaster, or hidden fixings that are invisible at a glance but will affect your depth reading.
| Preparation step | Why it matters |
|---|---|
| Remove window coverings | Gives unobstructed access to the full recess |
| Clear the sill | Prevents tape measure from catching on objects |
| Check with spirit level | Identifies uneven frames before ordering |
| Photograph the recess | Provides a visual record for your supplier |
How to measure shutter depth inside a window recess
Measuring recess depth is a three-part process: width, height, and depth. Each part requires multiple readings because very few windows are perfectly uniform.
Step 1: Measure the width
Measure width in three places: at the top of the recess, across the middle, and at the bottom. Record all three figures and note the smallest. Shutters are ordered to the smallest width to guarantee they will fit without forcing.
Step 2: Measure the height
Measure height on the left side, through the centre, and on the right side of the recess. Again, record all three and use the smallest figure. A difference of even 5mm between readings tells you the frame is not perfectly square, which affects how your shutters will sit.
Step 3: Measure the recess depth
This is the most critical reading for shutter operation. Place your tape measure at the front edge of the frame and extend it to the first point of obstruction. Measure at several positions across the width of the recess because depth can vary, particularly near window handles or tilt cranks. Record every reading in millimetres without rounding up or down.
Standard interior-mounted shutters require specific minimum depths depending on louvre size: a 64mm louvre needs at least 60mm of depth, a 76mm louvre requires 70mm, an 89mm louvre needs 75mm, and a 114mm louvre calls for 85mm minimum. These figures are not suggestions. If your recess falls short, the louvres will not tilt fully and the shutter will not function correctly.
Step 4: Check for square
Measure both diagonals of the window opening, from corner to corner. If the two diagonal readings match, the window is square. A difference of more than 5mm means the opening is out of square, and your supplier needs to know this before manufacturing begins.
The full sequence in order:
- Measure width at top, middle, and bottom. Note the smallest.
- Measure height at left, centre, and right. Note the smallest.
- Measure depth at multiple points, especially near handles. Note the smallest.
- Measure both diagonals and compare.
- Record everything in millimetres on your notepad.
- Photograph the recess from the front and from the side.
Pro Tip: Photograph the window recess in the evening when interior lighting is on. The light from inside the room reveals the depth of the recess and highlights any obstructions far more clearly than daytime photography.
What obstructions affect shutter depth, and how do you adjust?
Obstructions are the most common reason a shutter depth measurement needs adjusting. Identifying them before you order saves time and avoids the need for remedial work after delivery.
The most frequent obstructions inside a window recess include:
- Window handles and espagnolette locks, which often protrude 30mm or more into the recess
- Tilt and turn cranks on continental-style windows, which can extend significantly depending on the mechanism
- Ventilation slots and trickle vents built into the top of the frame
- Sash cords and pulleys on older timber sash windows
- Uneven plaster or render on the reveals, which creates variable depth across the recess
When the recess depth is too shallow for your chosen louvre size, two practical solutions exist. The first is an extended reveal fit, where the shutter panel is mounted proud of the window frame rather than inside the recess. This eliminates the depth constraint entirely. The second is the use of spacer blocks or build-outs, which are timber or composite strips fixed to the front face of the frame to bring the shutter forward and create the clearance the louvres need to tilt. Both methods are standard practice in the industry and do not compromise the finished appearance when fitted correctly.
For guidance on clearance and fit challenges, Shutterworld’s homeowner resource covers the most common fitting scenarios in detail.
Pro Tip: If a window handle is the only obstruction, measure its exact protrusion from the frame face and add 10mm to that figure. That total is the minimum depth your shutter panel must clear to operate without catching.
How do you measure shutter depth for out-of-square windows?
Non-standard windows require additional care during the measuring process. The step-by-step shutter measuring guide from Shutterworld covers these scenarios in full, but the core principles are straightforward.
Diagonal measurements are the primary tool for detecting an out-of-square opening. Measure from the top-left corner to the bottom-right corner, then from the top-right corner to the bottom-left corner. A difference of more than 5mm confirms the opening is a parallelogram or trapezoid shape rather than a true rectangle. This matters because a shutter panel built to the stated width and height will not sit flush against all four sides of the frame.
For unusually shaped windows, record the following additional information:
- Both diagonal measurements and the difference between them
- Which corner is the widest and which is the narrowest
- Whether the frame leans to the left or right when checked with a spirit level
- Any visible gaps between the existing window frame and the surrounding wall
Annotate a simple sketch of the window with all measurements written clearly against each edge. Include this sketch with your order. A supplier working from annotated drawings can adjust the shutter panel geometry or plan for on-site trimming during installation. Minor trimming of shutter edges is standard practice and does not affect the structural integrity of the panel.
After installation, a spirit level check confirms whether any minor adjustment is needed. Small gaps at the frame edge can be addressed with timber strips or cover beads, which are widely available and easy to fit. For more detailed guidance on shutter space requirements, including how to account for unusual reveals, Shutterworld’s dedicated resource is worth consulting before you finalise your measurements.
Key takeaways
Accurate shutter depth measurement requires recording the smallest reading at multiple points across the recess, checking for square using diagonal measurements, and identifying every obstruction before placing an order.
| Point | Details |
|---|---|
| Minimum depth by louvre size | A 64mm louvre needs 60mm depth; an 89mm louvre needs 75mm; always check before ordering. |
| Measure in three places | Take width and height readings at three positions each and always use the smallest figure. |
| Check diagonals for square | A difference of more than 5mm between diagonals means the window is out of square. |
| Obstructions change the depth | Handles and cranks reduce usable depth; extended reveal fit or spacer blocks resolve shallow recesses. |
| Photograph everything | Photos of the recess and obstructions give your supplier the detail they need to manufacture correctly. |
Why measuring feels harder than it is
I have spoken with hundreds of homeowners who put off ordering shutters for months because the measuring step felt too technical. The honest truth is that the process is methodical, not complicated. The mistakes I see most often are not errors of skill. They are errors of habit: measuring once instead of three times, rounding figures to the nearest 5mm, and forgetting to check the depth near the handle.
The reassuring reality is that most fitting issues are correctable. A panel that arrives 10mm too narrow can be remedied with a timber strip. An edge that is fractionally tight can be trimmed with a fine saw blade. These are not failures. They are normal adjustments that experienced fitters make on almost every job.
The one area where I would urge you not to cut corners is the louvre size decision. Choose a louvre that your recess can actually accommodate. A 114mm louvre looks striking, but it needs 85mm of clear depth to tilt. If your recess only gives you 70mm, order the 76mm louvre instead. The visual difference is minimal. The operational difference is significant.
My strongest advice: spend twenty minutes measuring carefully, photograph everything, and annotate a sketch. That preparation is worth more than any shortcut. When you hand those measurements to a specialist like Shutterworld, you are giving them everything they need to build a shutter that fits the first time.
— Ken
Bespoke shutters built to your exact measurements
Getting your measurements right is the foundation of a shutter installation you will be proud of for years. Shutterworld’s plantation shutter service is built around exactly that principle: every panel is manufactured to your precise dimensions, with full account taken of your recess depth, louvre size requirements, and any obstructions or unusual window shapes.
Whether you have a standard bay window or an arched or angled opening that has defeated every off-the-shelf solution, Shutterworld’s team brings over 25 years of bespoke craftsmanship to the job. Every order comes with a product and workmanship guarantee. If you would prefer a professional to take the measurements for you, Shutterworld’s bespoke internal shutter service includes an in-home survey at no extra cost. Book your free consultation and take the first step towards shutters that fit perfectly.
FAQ
What is the minimum recess depth for interior shutters?
The minimum depth depends on louvre size. A 64mm louvre requires 60mm, an 89mm louvre needs 75mm, and a 114mm louvre calls for 85mm of clear recess depth.
How do I check if my window is square?
Measure both diagonals of the window opening from corner to corner. If the readings differ by more than 5mm, the window is out of square and your supplier needs to know before manufacturing.
What should I do if my recess is too shallow?
Use an extended reveal fit, where the shutter mounts proud of the frame, or fit spacer blocks to bring the panel forward and create the clearance the louvres need to operate.
How many times should I measure each dimension?
Measure width and height at three positions each: top, middle, and bottom for width; left, centre, and right for height. Always order to the smallest reading.
Do window handles affect shutter depth measurement?
Yes. Handles and cranks protrude into the recess and reduce usable depth. Measure the exact protrusion of any handle and add 10mm to determine the minimum clearance your shutter panel must provide.