How to Measure Windows for Shutters — And Why You Probably Should Not Do It Yourself

Window measurement for shutters sounds like a straightforward task. You measure the width and height of the window, send the dimensions to a manufacturer and the shutters arrive ready to fit. It is how most online shutter retailers present the process — and it is why incorrect measurement is one of the most consistent causes of shutters that do not fit correctly.

The reality of accurate window measurement for bespoke shutters is more involved than measuring width and height at a single point. Period properties, older windows and the natural variation that exists in every domestic window opening require measurement at multiple points, assessment of the reveal depth and conditions, evaluation of frame condition and a judgement about how the shutter should be specified to fit the window as it actually exists rather than as it theoretically should be.

This guide from Miavalentina Interiors explains what accurate measurement actually involves, when self-measurement is and is not appropriate, and why professional survey almost always produces a better result.

What does accurate window measurement for shutters involve?

Accurate measurement for bespoke shutters requires measuring the window width at three points — top, middle and bottom — and the height at three points — left side, centre and right side. It requires measuring the reveal depth at multiple points across the reveal face. It requires assessing the squareness of the frame and the degree of any out-of-square variation. And it requires a judgement about how the shutter specification should account for the actual condition of the window rather than simply recording dimensions.

Why windows are not simply a width and a height

The assumption that a window is a consistent rectangle — the same width at top and bottom, the same height at left and right — is incorrect for most windows in most properties. It is especially incorrect for any window in a property built before the twentieth century.

Windows settle with the building. Frames shrink, expand and move with seasonal temperature and humidity changes over decades or centuries. Repainting fills corners and changes the effective dimensions of the opening. In older properties the original frame was often not perfectly square when it was fitted — the craftsmanship of earlier centuries was skilled but not machine-precise.

The practical consequence is that a Victorian sash window in Bury St Edmunds that measures eight hundred and forty millimetres wide at the top may measure eight hundred and fifty-two millimetres wide at the bottom. A window that measures one thousand one hundred millimetres high on the left side may measure one thousand and eighty-five millimetres on the right. These variations are invisible to the eye and would not be noticed on casual inspection — but they are immediately visible if a shutter panel is manufactured to one dimension and fitted to a window with different actual dimensions.

A shutter panel specified to the top width measurement that is twelve millimetres narrower than the bottom of the window will have a visible gap at the bottom of the reveal. A panel specified to the taller measurement will not close fully against the shorter side of the frame. In a Victorian sash window in a well-maintained period property where the finish quality is part of the appeal of the room, these fitting errors are unacceptable.

The reveal depth measurement

Beyond the window dimensions, the reveal depth — the distance from the face of the wall to the face of the window frame — determines which shutter frame profile can be used and how the shutter will sit within the window.

The reveal depth must be measured at multiple points across the reveal face because it is rarely consistent. A window in a Suffolk period property may have a reveal that is deeper at one corner than another, or where the plaster has built up over decades to reduce the depth at one side. The minimum depth at any point determines the maximum shutter frame profile that will fit.

The reveal depth also determines the air gap between the back of the shutter panel and the face of the glass — which affects both the thermal insulation performance of the installation and the clearance available for the window to open behind the shutter.

When self-measurement might be appropriate

Self-measurement for shutters is most likely to produce a correct result in the following specific circumstances:

Modern new build windows with consistent geometry — A contemporary new build window in a post-2000 property is likely to be genuinely square and consistent in dimension. The window frame was manufactured to precise tolerances and the reveal was built to a consistent depth. In this context, careful measurement at a single point for width and height, plus a reveal depth measurement, is likely to produce accurate dimensions.

Standard aluminium or uPVC replacement windows — Modern replacement window frames are manufactured to precise dimensions and rarely have the variation of original period frames. Self-measurement is more reliable for these windows than for original period frames.

Even in these cases, a professional survey will produce more accurate results and identify any variations that self-measurement might miss — but the risk of a significant error is lower than with original period windows.

When self-measurement is most likely to go wrong

Self-measurement is most likely to produce incorrect dimensions in the following situations — all of which are extremely common in Suffolk's housing stock:

Any original period window frame — Victorian, Georgian, Edwardian or older original timber frames have variation that single-point measurement does not capture. The out-of-square errors in older frames are the most common cause of shutters that do not fit correctly.

Cottage and rural property windows — The organic geometry of cottage windows — as discussed in our guide to shutters for cottages — makes single-point measurement particularly unreliable. These windows need multiple measurements at every point.

Bay windows — Bay window measurement requires not just the dimensions of each panel but the angles between panels — measurements that most homeowners do not have the tools or experience to take accurately.

Windows with existing internal shutters or window boards — The presence of existing fixtures in the reveal affects the usable dimensions and the shutter specification. These need to be assessed and accounted for in the measurement.

Any window where the reveal depth is close to the minimum for a standard frame — If the reveal is just adequate for a standard frame at one point but shallower at another, a professional survey will identify this and specify accordingly. Self-measurement that takes one depth reading at the centre of the reveal may miss a shallower depth at the corner that would prevent the frame from fitting.

What happens when measurement goes wrong

The consequences of incorrect self-measurement range from minor inconvenience to significant cost.

If the shutter panel is too narrow for the window — specified to the narrowest measurement rather than accounting for the full width variation — there will be a gap between the panel edge and the reveal at the wider end. This gap is visible and unacceptable in a quality installation.

If the shutter panel is too wide for the window — an uncommon error but possible if measurement is taken at the widest point — the panel will not fit within the reveal and cannot be installed without adjustment or replacement.

If the reveal depth was underestimated and the shutter frame is too deep for the actual reveal, the frame will not fit flush and the shutter will sit proud of the wall — or in some cases cannot be fitted at all without adjustment to the reveal.

In each case the resolution involves either returning the shutters to the manufacturer for adjustment — possible but time-consuming and sometimes incurring additional cost — or having the installation adjusted on site, which may not be possible without remanufacture.

The cost of a professional survey is covered by Miavalentina Interiors at no charge. The cost of remanufacturing shutters because of a measurement error is not.

What a Miavalentina Interiors survey includes

Our free home survey covers every measurement and assessment needed to specify shutters correctly for any window type in any property.

Dimension measurement — width at three heights, height at three widths, for every window to be shuttered.

Reveal depth assessment — measured at multiple points across the reveal face to identify the minimum depth and any variation.

Frame condition assessment — the condition of the existing window frame is assessed to identify any issues that would affect the shutter specification or fitting method.

Squareness assessment — the degree of out-of-square variation is measured and factored into the panel specification.

Style and finish discussion — we discuss the style options, louvre sizes, paint finish and any other specification decisions with you in the context of your actual windows and your home.

Written specification — everything agreed at the survey is confirmed in writing in a full specification document before any order is placed.

The survey typically takes between one and two hours for a standard domestic property and covers every window you are considering. There is no obligation and no pressure — if at the end of the survey you decide not to proceed, there is no cost and no obligation.

We offer free no-obligation home surveys across Suffolk, including Southwold, Aldeburgh, Woodbridge, Bury St Edmunds, Walberswick and Lavenham. Book your free survey here and we will visit at a time that suits you, including evenings and weekends.