How to Choose the Right Louvre Size for Your Shutters

Louvre size is the shutter specification decision that most buyers do not know they need to think about — and one of the most visible when it is wrong. A shutter with louvres that are too large for the window looks heavy and out of proportion. A shutter with louvres that are too small for a large window looks fussy and restless. Getting it right is the difference between shutters that look like they were made for the window and shutters that look like they were made for a different window.

This guide from Miavalentina Interiors explains the available louvre sizes, what each one suits and how to choose correctly for your specific windows and property type.

What louvre sizes are available?

The three standard louvre sizes used in the shutter industry are forty-seven millimetres, sixty-three millimetres and eighty-nine millimetres. These refer to the width of each individual louvre blade — the horizontal slat that rotates to control light and privacy. A forty-seven millimetre louvre is the narrowest standard option, an eighty-nine millimetre louvre is the widest. Some manufacturers offer intermediate sizes or custom options, but these three cover the vast majority of domestic shutter installations.

Forty-seven millimetre louvres — when to use them

Forty-seven millimetre louvres are the smallest standard size and suit smaller, more intimate window proportions. They create more louvres per panel height than larger sizes — a full height shutter panel on a standard window might have fifteen to eighteen forty-seven millimetre louvres compared to ten to twelve sixty-three millimetre louvres and seven to nine eighty-nine millimetre louvres.

The visual effect of forty-seven millimetre louvres is fine-grained and detailed — the horizontal lines are closely spaced and the overall impression is one of delicacy and refinement. This suits specific contexts well and looks wrong in others.

Best suited to:

Cottage windows — the intimate scale of a Suffolk cottage window in Aldeburgh, Walberswick or Lavenham suits the fine grain of forty-seven millimetre louvres well. A larger louvre in a small cottage window looks disproportionate — too few louvres across too small a panel height creates a heavy, coarse appearance.

Small casement windows — Edwardian and some Victorian casement windows with a total height below nine hundred millimetres generally benefit from the finer proportion of forty-seven millimetre louvres.

Bathroom and kitchen windows — Smaller functional windows in any property type suit forty-seven millimetre louvres where the window height is less than a metre.

Less suited to:

Large Victorian or Georgian sash windows — forty-seven millimetre louvres in a full-height Victorian sash window create a very high louvre count that can look restless and over-detailed against the bold glazing bars and proportions of the period window.

Contemporary large windows — modern windows with expansive glazed areas look better with bolder louvre sizes that suit the scale of the opening.

Sixty-three millimetre louvres — the versatile middle ground

Sixty-three millimetre louvres are the most widely used size across the shutter industry and the default recommendation for the majority of domestic windows. They suit a broad range of window sizes and property types and very rarely look wrong — which is why they are the starting point for most specifications.

The visual effect of sixty-three millimetre louvres is balanced and proportionate in most contexts. The horizontal lines are clearly visible as a design element without dominating the overall appearance of the shutter. When open they allow good light transmission without the very wide gaps of the eighty-nine millimetre option.

Best suited to:

Standard Victorian sash windows — the sixty-three millimetre louvre suits the proportions of the typical Victorian sash window well. It creates a louvre count that reads as considered and architectural rather than either fussy or heavy.

Edwardian wider sash windows — the slightly wider Edwardian window benefits from sixty-three millimetre louvres in most cases, though the larger eighty-nine millimetre option should also be considered for the grandest Edwardian windows.

Standard bedroom and living room windows in any property type — sixty-three millimetre is the safe and correct choice for any window between approximately nine hundred millimetres and one thousand five hundred millimetres in height.

New build windows — contemporary new build windows typically suit sixty-three millimetre louvres across most standard window sizes.

Less suited to:

Very small windows — where forty-seven millimetre would be more proportionate.

Very large windows and bay windows — where eighty-nine millimetre makes a stronger, more appropriate statement.

Eighty-nine millimetre louvres — bold and architectural

Eighty-nine millimetre louvres are the largest standard size and the one that makes the strongest visual statement. Fewer louvres per panel, wider individual blades and a more dramatic horizontal emphasis — eighty-nine millimetre louvres suit large windows and spaces where a bold, architectural appearance is appropriate.

The visual effect of eighty-nine millimetre louvres is striking and contemporary. The wide blades create strong horizontal lines that suit large windows, high ceilings and generous rooms. When open they allow excellent light transmission — the wider gaps between louvres admit more light than smaller sizes at the same louvre angle.

Best suited to:

Large Georgian sash windows — Georgian windows are typically larger than Victorian equivalents, and the bolder eighty-nine millimetre louvre suits the grander proportions of Georgian domestic architecture well. In a Georgian drawing room in Bury St Edmunds or Woodbridge, eighty-nine millimetre louvres make a strong, architecturally appropriate statement.

Bay windows — the scale of a bay window benefits from the bolder louvre size. Eighty-nine millimetre louvres across a three or four panel bay create a unified, architectural appearance that smaller louvres cannot match at that scale.

Contemporary large windows and bifold doors — the clean, bold lines of eighty-nine millimetre louvres suit the architectural language of contemporary buildings with large glazed areas. Tracked shutters across a wide contemporary opening look most impressive with the larger louvre size.

High-ceilinged period rooms — any room with ceiling height above three metres benefits from eighty-nine millimetre louvres that suit the vertical scale of the space.

Less suited to:

Small windows — eighty-nine millimetre louvres in a small window create very few louvres per panel and the result looks sparse and poorly proportioned.

Cottage properties — the intimate character of a cottage window is overwhelmed by the bold scale of eighty-nine millimetre louvres.

How to choose — a practical framework

If you are unsure which louvre size is right for your windows, the following framework covers most situations accurately:

Window height under 900mm — forty-seven millimetre louvres

Window height 900mm to 1,500mm — sixty-three millimetre louvres in most cases, forty-seven millimetre for cottage or intimate character windows

Window height 1,500mm to 2,200mm — sixty-three or eighty-nine millimetre depending on window width and room scale. Wider windows favour eighty-nine millimetre. Narrower windows favour sixty-three millimetre.

Window height over 2,200mm — eighty-nine millimetre louvres in most cases

Bay windows regardless of individual panel height — eighty-nine millimetre in most cases, sixty-three millimetre for smaller or more intimate bay windows

Cottage windows regardless of height — forty-seven millimetre in most cases

This framework covers the majority of decisions correctly. The cases where it needs to be refined are the ones where the room character, the architectural style or the overall design scheme pulls the specification in a different direction — and these are the cases that the survey stage is designed to address.

Why this decision matters more than people realise

The louvre size is one of those specification decisions that is invisible when it is right and immediately noticeable when it is wrong. Homeowners who receive shutters with the wrong louvre size often struggle to articulate exactly what looks off — they know the shutters look wrong but cannot identify why. In most cases the louvre size is the answer.

This is one of the arguments for professional survey over online ordering. A website cannot assess your specific window proportions, your ceiling height, your room character and your existing architectural details and make the right louvre size recommendation. A surveyor standing in your room with samples of all three sizes can make that assessment immediately and accurately.

We bring louvre samples to every survey we carry out across Suffolk — you can hold them against your window and your wall and see the difference directly before committing to a specification. It is one of the most useful parts of the survey process and one that consistently helps homeowners make a decision they are confident about.

Louvre size and light transmission

Beyond appearance, louvre size has a practical effect on light transmission that is worth understanding.

Larger louvres transmit more light when open because the gaps between the blades are wider relative to the blade width. An eighty-nine millimetre louvre at the same open angle as a forty-seven millimetre louvre lets in more light because more of the panel area is open space rather than blade surface.

For rooms where maximum natural light when the shutters are open is important — a north-facing room, a room with limited window area relative to floor space — larger louvres are worth considering on this practical basis as well as the aesthetic one.

For rooms where privacy at an angle matters — where the room is slightly below street level or where the window is very close to a public space — smaller louvres provide better privacy at equivalent open angles because the narrower gaps between blades reduce the diagonal line of sight into the room.

We assess louvre size at every survey we carry out across Suffolk, including Southwold, Aldeburgh, Woodbridge, Bury St Edmunds, Walberswick and Lavenham. Book your free survey here and we will bring samples so you can see all three sizes in your own home before making a decision.