Shutter sizes and fit: measure right, first time

Woman measuring window recess for shutters

For most UK recessed windows, the correct approach is an inside-mount (in-frame) fit measured to the smallest of three width readings and three height readings, recorded to the nearest millimetre. Get that single rule right and the rest of the process follows naturally.

Before you pick up a tape measure, run through this quick checklist:

Check squareness first. Measure both diagonals of the recess. If they differ by 15mm or more, the window may need a Z-frame or a professional survey.
Always use the smallest reading. Take width at the top, middle, and bottom; take height at the left, centre, and right. Order to the smallest in each direction.
Note every obstruction. Handles, tilt mechanisms, deep sills, and internal beading all affect which fit type is possible.
Measure recess depth. In-frame shutters need adequate depth; if the recess is too shallow, face-fit or Perfect Fit (no-drill) shutters may be the only workable option.
Consider a professional survey for anything complex. Shutter World offers an in-home survey with measured templates and a workmanship guarantee, removing the guesswork entirely.

Is your window suitable for Perfect Fit, in-frame or face-fit shutters?
How to measure for shutters: inside-mount, face-fit and Perfect Fit
How do panels, panel widths and louvre sizes affect your shutters?
Frame depth, brackets, handles and hardware: what you need to measure
Perfect Fit, in-frame or face-fit: which installation should you choose?
When should you book a Shutter World professional survey?
Common measuring mistakes and how to avoid them
Key takeaways
Why a professional survey often saves more than it costs
Shutter World’s survey and installation service: how it works
Further reading and Shutter World resources
FAQ

Is your window suitable for Perfect Fit, in-frame or face-fit shutters?

Choosing the right fit type before you measure saves you from capturing the wrong dimensions entirely. Each installation method has specific requirements, and your window’s physical characteristics will often make the decision for you.

Perfect Fit (no-drill) shutters clip directly into the window frame without screws or brackets. They suit uPVC and aluminium frames with a standard rubber bead, but the frame must pass a few checks:

Run a credit card around the rubber bead where it meets the glass. If the bead overlaps the frame by less than the minimum clearance specified by the manufacturer, Perfect Fit is not suitable.
The frame must be square and plumb. Use a spirit level on both vertical sides.
Tilt-and-turn or top-hung windows with inward-opening sashes are generally incompatible with Perfect Fit systems because the shutter would obstruct the opening arc.
Deep sills or projecting handles can prevent the Perfect Fit bracket from seating flush.

In-frame (rebate) shutters sit within the recess and are the most popular choice for UK timber and uPVC windows with adequate depth. The recess must be deep enough to accommodate the frame and panel without fouling the sash when it opens. Measure recess depth at the left, centre, and right of the reveal; if readings vary significantly, note the shallowest point.

Face-fit shutters mount on the wall or window board outside the recess. They work where the recess is too shallow for in-frame fitting or where the homeowner wants to cover an oversized or irregular opening. The trade-off is a more prominent profile that sits proud of the wall.

Pro Tip: If your diagonal measurements differ noticeably, or if the reveal tapers from top to bottom, book a professional survey rather than attempting to compensate with DIY adjustments. A Z-frame can accommodate moderate run-off, but a surveyor will confirm whether it is the right solution for your specific window.

How to measure for shutters: inside-mount, face-fit and Perfect Fit

Accurate window shutter measurements are the foundation of a good fit. Follow these steps for each installation type, and record every figure in millimetres.

Inside-mount (in-frame) shutters

Measure width at three points. Hold a metal tape measure horizontally across the recess at the top, middle, and bottom. Record all three readings.
Use the smallest width. This is the figure you submit when ordering.
Measure height at three points. Measure vertically on the left side, the centre, and the right side of the recess.
Use the smallest height. Again, the smallest reading protects against a panel that will not close.
Check squareness. Measure both diagonals (corner to corner). A variance of 15mm or more signals a non-square window requiring a Z-frame or survey.
Measure recess depth. Take three depth readings across the reveal at left, centre, and right, and note the shallowest.
Record mid-rail position. If you want a mid-rail (a horizontal divider that allows the top and bottom louvres to operate independently), measure from the sill to the proposed mid-rail height and record it separately on your order form.
Note handle position. Measure from the sill to the centre of the handle and record the handle projection from the frame face.

Outside-mount (face-fit) shutters

Measure the full width of the area you want to cover, including any overlap onto the wall or window board.
Measure the full height from the top of the intended coverage area to the sill or floor, again including any desired overlap.
Note the distance from the wall face to any obstructions (radiators, shelves, furniture) that could prevent the shutter from opening fully.

Perfect Fit (no-drill) shutters

Measure the visible glass width and height within the frame rebate, not the full frame.
Check the rubber bead clearance on all four sides.
Confirm the frame is plumb and square using a spirit level.

Measurement	Where to take it	Which reading to use
Width	Top, middle, bottom of recess	Smallest of the three
Height	Left, centre, right of recess	Smallest of the three
Depth	Left, centre, right of reveal	Shallowest reading
Mid-rail height	Sill to proposed divider	Exact figure, noted separately

Pro Tip: Use a rigid metal tape rather than a fabric or retractable cloth tape. Metal tapes hold straight across wide openings and give consistent readings. Stick a small piece of masking tape at each measurement point to mark where you took the reading, so you can re-check quickly if a figure looks wrong.

For arched, bay, triangular, and skylight windows, the measuring process differs considerably. Bay windows require individual measurements for each facet, including the angle between sections. Arched windows need a height measurement to the apex and a width at the widest point, plus a template in most cases. For these shapes, a professional survey is strongly recommended.

How do panels, panel widths and louvre sizes affect your shutters?

The number of panels and the size of the louvres shape how your shutters look, how much light they let in, and how stable they feel in use. These are not purely aesthetic choices.

Louvre sizes in the UK market typically run from 47mm (roughly 1.9 inches) up to 114mm (4.5 inches), with 89mm (3.5 inches) and 114mm (4.5 inches) being the most widely specified. Here is how they compare in practice:

89mm (3.5") louvres give finer light control and suit smaller windows well. When closed, they block more light and offer greater privacy because the blades overlap more completely.
114mm (4.5") louvres open to a wider angle, giving a clearer view through the glass and better airflow. They suit taller windows where the larger blade scale looks proportionate. When open, the view is noticeably less obstructed.
Smaller louvres (47mm–64mm) are typically used on café-style or tier-on-tier shutters for smaller panes, period properties, or where a traditional cottage look is the goal.

Matching louvre size to window height keeps the proportions balanced. As a general guide, choose louvre size to complement the window’s scale: taller windows carry larger louvres well, while compact windows look better with 64mm or 89mm blades.

Maximum panel widths matter for structural stability. A single shutter panel that is too wide will bow, warp over time, or feel flimsy when operated. When a window exceeds the recommended single-panel width, the solution is to split into two panels with a central stile, or to add mid-stiles for very wide openings. This is standard practice for bay windows and wide picture windows.

The number of panels also affects how the shutters fold back when open. A four-panel configuration on a wide window folds into a compact stack at each side, keeping the glass clear. Two panels on the same window would project further into the room when open.

Frame depth, brackets, handles and hardware: what you need to measure

Hardware details are where many DIY measurements fall short. A shutter that fits the opening perfectly can still fail to function if a handle projects into the panel’s path or if the recess is shallower than the frame requires.

Minimum recess depth for in-frame shutters varies by frame profile and manufacturer specification. Measure the depth at three points across the reveal (left, centre, right) and use the shallowest reading as your working figure. If any point is too shallow for in-frame fitting, face-fit or Perfect Fit becomes the appropriate choice.

Face-fit clearance requires enough wall depth between the shutter frame and any adjacent obstruction (architrave, radiator, furniture) to allow the panels to open fully to at least 90 degrees.

Hardware checklist to photograph and share when ordering:

Handle type (lever, espagnolette, tilt bar, or cockspur) and its projection from the frame face in millimetres
Sill projection: how far the sill extends into the room beyond the frame face
Window bead type: flat bead, sculptured bead, or Georgian bar, and whether it is internally or externally beaded
Any internal beading that reduces the usable recess depth
Tilt-in or tilt-and-turn mechanism: note the arc of travel so the shutter frame does not obstruct it
Restrictor arms or child safety locks fitted to the frame

Providing photographs of each of these details alongside your measurements gives the manufacturer everything needed to produce a shutter that works first time. Noting handle projection on the measurement sheet avoids fit clashes that commonly cause last-minute onsite adjustments.

Perfect Fit, in-frame or face-fit: which installation should you choose?

Each installation type has a distinct set of advantages, and the right choice depends on your window’s physical characteristics, your aesthetic preference, and how permanent you want the installation to be.

Perfect Fit (no-drill)

Pros:

No drilling into the frame; fully reversible
Clean, integrated look that sits flush with the frame
Fast to install and remove

Cons:

Only compatible with uPVC and aluminium frames with a standard rubber bead
Not suitable for tilt-and-turn or inward-opening windows
Limited to frame sizes and profiles the system accommodates

Best for: modern uPVC windows in good condition where a non-permanent, tidy solution is the priority.

In-frame (rebate) fit

Pros:

Sits neatly within the recess for a built-in appearance
Suitable for timber, uPVC, and most standard window types
The most popular choice for UK homes

Cons:

Requires adequate recess depth
Non-square windows may need a Z-frame, adding cost
More complex to install than Perfect Fit

Best for: standard rectangular recessed windows with sufficient depth, where a permanent, high-quality finish is the goal.

Face-fit

Pros:

Works regardless of recess depth
Can cover oversized or irregular openings
Useful where the reveal is too shallow or damaged for in-frame fitting

Cons:

Sits proud of the wall, which some homeowners find less elegant
Requires wall fixings and careful alignment

Best for: shallow reveals, non-standard openings, or where in-frame fitting is not possible.

Typical timeline from measure to installation: bespoke shutters are made to order, so lead times from confirmed measurement to delivery and installation typically run several weeks, depending on the complexity of the order and the manufacturer’s current schedule. Face-fit and Perfect Fit installations are generally quicker to complete on site than in-frame fitting, which may require more precise carpentry.

When should you book a Shutter World professional survey?

Some windows are straightforward to measure yourself. Others are not, and the cost of getting it wrong on a bespoke order is significant. Here are the decision rules:

Book a professional survey if:

Your diagonal measurements differ by 15mm or more
The window is arched, triangular, circular, or part of a bay
The reveal depth varies by more than a few millimetres across the width
There are complex obstructions (deep sills, projecting handles, tilt-in mechanisms) you are unsure how to record
You have low confidence in your measurements after re-checking
The window is a skylight or roof light requiring specialist templates

DIY measurement is usually sufficient if the windows are standard rectangular, the recess is square and consistent, and you are confident taking three-point width and height readings with a metal tape.

What Shutter World’s professional survey includes: an experienced fitter visits your home, takes precise on-site measurements using professional tools, creates accurate templates for any complex shapes, checks frame depth and hardware compatibility, and produces a full specification for manufacture. Every installation backed by Shutter World comes with a product and workmanship guarantee, giving you confidence that the fit will be right.

Before your surveyor arrives:

Open and close every window to be fitted so the fitter can check the full range of movement
Remove curtains, blinds, and any temporary coverings from the windows
Clear the area around each window for easy access
Note any concerns or preferences (mid-rail position, louvre size, finish) to discuss on the day

For unusually shaped or tricky windows, a survey is not just convenient; it is the reliable path to a shutter that fits and functions as intended.

Common measuring mistakes and how to avoid them

Most measurement errors are simple and preventable. Catching them before you submit an order saves time, money, and frustration.

Frequent mistakes:

Using a fabric or retractable cloth tape. These sag across wide openings and give readings that can be several millimetres out. Always use a rigid metal tape.
Not measuring to the nearest millimetre. Rounding to the nearest 5mm or 10mm introduces errors that compound across width, height, and depth.
Ignoring run-off. A reveal that is wider at the top than the bottom is not square. Ordering to the average rather than the smallest reading produces a panel that will not close properly.
Forgetting to record mid-rail position separately. The mid-rail height is not derived from the overall height; it must be measured independently from the sill.
Mis-noting handle projection. Recording that a handle exists is not enough. The projection distance in millimetres determines whether the panel will clear it.
Measuring only once. Always re-measure at least one reading independently to confirm it.

Quick fixes before you order:

Re-measure both diagonals and compare them. If they differ, re-measure the width and height readings too.
Photograph every obstruction (handle, sill, bead, restrictor) and attach the images to your order or survey booking.
Mark your measurement points with masking tape so you can return to exactly the same spot.
Run through the full three-point width and height checklist one final time, ticking off each reading.

Key takeaways

Getting shutter sizes and fit right comes down to one discipline: always measure width and height at three points each, use the smallest reading in every direction, and record depth and obstructions before you order or book.

Point	Details
Use the smallest reading	Measure width at top, middle, and bottom; height at left, centre, and right; always order to the smallest figure.
Check squareness before choosing fit	If diagonals differ by 15mm or more, a Z-frame or professional survey is needed before ordering.
Match louvre size to window scale	Taller windows suit 114mm (4.5") louvres; compact windows look better with 89mm (3.5") or smaller blades.
Record every obstruction in millimetres	Handle projection, sill depth, and bead type must be noted precisely to avoid fit clashes on installation day.
Shutter World survey for complex windows	For bay, arched, or non-square windows, Shutter World’s in-home survey with measured templates and a workmanship guarantee removes the risk.

Why a professional survey often saves more than it costs

There is a persistent assumption among homeowners that measuring for shutters is straightforward enough to do entirely alone, and for a standard rectangular uPVC window in good condition, that is often true. But the windows that cause problems are rarely the ones people expect.

On site, the surprises tend to be the same ones repeated: a reveal that looks square but tapers by 20mm from top to bottom, a handle that projects 35mm into the panel’s path, or an internal bead that reduces the usable depth by just enough to make in-frame fitting impossible. None of these are visible from a photograph or obvious from a basic tape measure. They only become apparent when someone who knows what to look for examines the window in person.

The financial logic is straightforward. A bespoke shutter order that has to be remade because of an incorrect measurement costs significantly more than a survey. Beyond the direct cost, there is the delay of waiting for a replacement and the frustration of living without window coverings in the interim. For a complex bay window or an arched frame, the gap between a good measurement and a poor one is the difference between shutters that sit perfectly and shutters that simply do not close.

Shutter World’s professional survey and installation service is built around eliminating that risk. Over 25 years of fitting experience means the team has encountered virtually every window type and obstruction combination. The workmanship guarantee is not a marketing phrase; it is the practical result of measuring correctly from the start.

Shutter World’s survey and installation service: how it works

Shutter World’s end-to-end service takes you from bare window to finished, guaranteed installation without the risk of a costly remeasure. An experienced fitter visits your home, takes precise measurements, checks frame depth and hardware compatibility, and produces the full specification for your bespoke shutters. There is no guesswork and no ambiguity in the order.

Once the survey is complete, your shutters are manufactured to those exact dimensions, whether you are ordering from the durable Seattle range or the premium hardwood Montana collection. Plantation shutters and bespoke shapes alike are covered under the same product and workmanship guarantee.

To book, have the following ready: the rooms and windows you want to cover, any preferences on louvre size or finish, and access to each window on the day of the survey. You can request a quote or book your survey online at shutterworld.co.uk or by phone. One supplier, one point of contact, from first measurement to final installation.

FAQ

How do I know what size shutters I need?

Measure your window recess width at the top, middle, and bottom, and height at the left, centre, and right. Order to the smallest reading in each direction, recorded to the nearest millimetre.

What is the difference between 3.5" and 4.5" shutters?

The figures refer to louvre width. The 89mm (3.5") blade gives finer light control and suits smaller windows; the 114mm (4.5") blade opens wider for a clearer view and better airflow, and suits taller windows where the larger scale looks proportionate.

Are shutters outdated in 2026?

Plantation shutters remain one of the most popular window coverings in UK homes, valued for their light control, privacy, thermal performance, and the clean, timeless look they bring to period and contemporary properties alike.

How do I measure and fit shutters correctly?

Use a rigid metal tape to take three width readings (top, middle, bottom) and three height readings (left, centre, right) of the recess. Order to the smallest in each direction, note recess depth and all obstructions, then choose your fit type: in-frame, face-fit, or Perfect Fit (no-drill) based on your window’s depth and frame type.