Measuring Bay Windows for Plantation Shutters

Bay windows combine several shutter faces, so the key is to take each section accurately while also planning how the frames meet at the internal corners. We use special bay posts to join the panels together.

In this article

• What is a bay window?
• Measuring a corner window
• Inside L-frame
• Windows with a sill or full-length windows
• Inside Z-frame
• Outside L-frame
• Multiple panels
• Custom panel widths

What Is a Bay Window?

A bay window is made up of three window sections that project out from the room, with the side sections meeting the centre section at approximately 45° angles . Use that result for this step.

Because all three sections connect together, they need to be measured and planned as one coordinated shutter arrangement, so the frames, bay posts and panels meet correctly. Use that result for this step.

For measuring, divide the bay into three sections: A to B = Left Window (L) , B to C = Centre Window (M) and C to D = Right Window (R) . Use that result for this step.

Determine if your corner window is 45 degrees

Check that your bay corner is in fact 45 degrees by placing a folded a4 paper in or against the corner. Use that result for this step.

Measuring for a Corner Window

Corner windows need more care than a single rectangular opening, but the process is easier if you treat each face as a separate window and always work from left to right.

Before taking readings, select whether the shutters is inside mounted or outside mounted . You will need a metal tape measure, something to note the figures and a pencil for marking the corner reference points.

Measuring for an Inside L-Frame: Recess-Fit Guide

For the dimensions used in the order, for this step, for an Inside L-frame , readings are taken inside the window recess , using the front edge of the recess rather than measuring back at the glass. Use that result for this step.

For this shutter measurement, at this stage, as a simple clearance rule, aim for approximately 70mm of clear recess depth . If the depth is tighter or there are handles, winders or other obstructions, you may still be able to mount the shutter inside with less, check Handles, Winders & Other Shutter Obstructions for more information. Use that result for this step.

1. Measure the width of the left window (A)

• Begin at the inside edge of the left-hand recess. Take note of the architrave lip in illustrations below if your window has architraves. Use that result for this step.
• Take the width through to the corner where the two recess faces intersect.
• Take this width in two positions (Top and Bottom of your window) as windows can vary. Work from the smallest of your readings for each section. Use that result for this step.
• Label that left corner reference as Measure Point A (Left).

2. Measure the width of the right window (B)

• For the adjoining section, begin at the right-hand end of Measure Point L (A), where A and B meet through the centre.
• Take to the inside edge at the far end of the right-hand recess. Take note of the architrave lip in illustrations below if your window has architraves. Use that result for this step.
• Take this width in two positions (Top and Bottom of your window) as windows can vary. Work from the smallest of your readings for each section. Use that result for this step.
• Label the right corner reference as Measure Point B (Right).

3. Measure the drop

Run the tape from bottom to top in three different positions across each opening.

4. Record the smallest drop

Use the smallest of the three drop readings. Enter the measured figure only—do not make your own manufacturing deduction.

Windows With a Sill or Full-Length Windows

A projecting window sill , or a full-height opening where there is no simple front corner edge to work from, means you first need to establish a consistent measuring point through the corner. Use that result for this step.

1–4. Establish the corner measuring point

1. Start from the left-hand recess.
2. Stretch a straight piece of string along the sill or lower reference line toward the opposite pane and hold it in place.
3. Repeat the process from the right-hand recess using a second straight string line.
4. Where the two string lines cross becomes the corner reference for the left- and right-hand width measurements.

If measuring a full length window to the floor, use the same premise as above, and imagine the window sill is the floor. Use that result for this step.

5. Check the measuring point

Check the clearance to the window in four positions around the reference point. The clearances should agree. If they do not, adjust the string position slightly and check again until the reference is consistent. Use that result for this step.

6. Measure the left and right widths

Once the reference point is confirmed, follow the Inside L-frame width method above for Window L and Window R, using this point as the shared corner reference. Use that result for this step.

7. Ordering

To order , enter your readings for each separate window section that makes up the corner window (A + B) on the ordering page and tick the “Bay / Corner” window option. You will then have A and B as separate items in your cart, enter the same room name and which side the window is so we can match them. Use that result for this step.

Measuring for an Inside Z-Frame: When & Why to Use It

At this point in the shutter measure, as you work through the guide, an Inside Z-frame wraps around the front edge of the recess, so the corner measuring points are determined by the actual Z-frame profile rather than simply using the recess intersection. Use that result for this step.

As a simple clearance rule for a Z-frame, aim for approximately 65mm of clear recess depth . If the depth is tighter or there are handles, winders or other obstructions, you may still be able to mount the shutter inside with less, check Handles, Winders & Other Shutter Obstructions for more information. Use that result for this step.

1. Measure the width of the left window (A)

• Begin at the inside edge of the left-hand recess. Take note of the architrave lip in illustrations below if your window has architraves. Use that result for this step.
• Follow the face edge of the architrave and measure through to the corner where the two recess faces meet.
• Take this width in two positions (Top and Bottom of your window) as windows can vary. Work from the smallest of your readings for each section. Use that result for this step.
• Label that left corner reference as Measure Point A (Left).

2. Measure the width of the left window (B)

• For the adjoining section, begin at the right-hand end of Measure Point L (A), where A and B meet through the centre.
• Take to the inside edge at the far end of the right-hand recess. Take note of the architrave lip in illustrations below if your window has architraves. This is along the edge of the face of the architrave. Use that result for this step.
• Take this width in two positions (Top and Bottom of your window) as windows can vary. Work from the smallest of your readings for each section. Use that result for this step.
• Label the right corner reference as Measure Point B (Right).

4. Measure the drop

• Measure bottom to top from inside the recess.
• Take the drop in three positions.
• Use the smallest of the three measurements.

Measuring for an Outside L-Frame: Face-Fit Guide with an Architrave

For this shutter measurement, at this stage, for an Outside L-frame fitted to an architrave, use the outside edges of the architrave as your measuring references. Use that result for this step.

1. Measure the width of the left window (L)

• Begin from the outside edge of the left architrave.
• Run the tape from that edge to the corner where the two architraves meet (A to B in the diagram).
• Take this width in two positions. (Top and Bottom widths). Work from the largest of the two as we want the frame to fully cover the architrave at all points when fitted. Use that result for this step.
• Mark the corner as Measure Point L (A).

2. Measure the width of the right window (R)

• Start the next reading at the right-hand end of Measure Point L (B).
• Continue from B to the outside edge of the right architrave (B to C).
• Take this width in two positions. (Top and Bottom widths). Work from the largest of the two as we want the frame to fully cover the architrave at all points when fitted. Use that result for this step.
• Mark the corner as Measure Point R (B).

3. Measure the drop

Run the tape from the outside edge of the bottom architrave to the outside edge of the top architrave in three positions. Work from the largest of your three readings on each section.

4. Record the largest drop

For this outside-mount architrave method, note the largest of the three drop readings. This is so we ensure the shutter will cover all parts of the architrave for aesthetic reasons.

5. Ordering

To order , enter your readings for each separate window section that makes up the corner window (A + B) on the ordering page and tick the “Bay / Corner” window option. You will then have A and B as separate items in your cart, enter the same room name and which side the window is so we can match them. Use that result for this step.

Measuring for an Outside L-Frame: Face-Fit Guide for a Square Set window

For an Outside L-frame fitted to a square-set window (no architraves), take the window opening first, then add the required allowances to these readings so the frame sits neatly around the outside of the opening. More details are provided below.

1. Measure the width of the left window (A)

• Begin at the outside edge of the window opening.
• Measure through to the corner where the two windows meet (A to B in the diagram).
• Take this width in two positions. (Top and Bottom widths). Work from the largest of the two as we want the frame to fully cover the architrave at all points when fitted. Use that result for this step.
• Add 42mm (X) to the width for this section so the shutter frame projects beyond the opening as required.
• Use Measure Point L (A) for this corner. The required reading is (A to B) + 42mm.

2. Measure the width of the right window (B)

• Begin at the outside edge of the window opening.
• Measure through to the corner where the two windows meet (B to C in the diagram).
• Take this width in two positions. (Top and Bottom widths). Work from the largest of the two as we want the frame to fully cover the architrave at all points when fitted. Use that result for this step.
• Add 42mm (X) to the width for this section so the shutter frame projects beyond the opening as required.
• Use Measure Point R (B) for this corner. The required reading is (B to C) + 42mm.

3. Measure the drop

Take the window opening in three positions.

4. Record the largest drop and add allowance for the frame

For this shutter measurement, at this stage, work from the largest of your three readings on each section on the step above. Then add 84mm to this reading.

4. Record the largest drop and add allowance for the frame

At this point in the shutter measure, for the order, work from the largest of your three readings on each section on the step above. Then add 84mm to this reading.

Multiple Panels

Shutter Panels

Plantation shutters are divided into individual panels. For windows wider than around 950mm , more than one panel will generally be required. Individual panels may be made up to approximately 900mm wide , with the surrounding frame adding a little extra overall width. Use that result for this step.

Where possible, plan the shutter panel layout so it follows the vertical divisions of the existing window. Use that result for this step.

What if the window panes are uneven?

If the existing panes are not evenly divided, custom panel widths may be achieved by placing the T-posts in custom locations to align more naturally with the window layout. Use that result for this step.

Multiple Panels for Corner Windows

The corner post extends slightly into both window faces. This affects the panels closest to the corner and needs to be considered when you want panel joins to line up with window mullions. Use that result for this step.

1. Equal-width panels suit layouts where only a small number of panels is needed on each side and precise alignment with the window mullions is not required.
2. Use custom-width panels when the T-posts or panel joins need to align with unequal vertical window divisions. It is normal for the panel closest to the corner to finish narrower than the others.

Measuring Custom T-Post locations

Take cumulative panel measurements from the left-hand side.

For the left section of your corner window:

• Inside mount: use the inside-left edge of the recess as the starting point.
• Outside mount with architrave: start at the outer-left architrave edge.
• Square-set outside mount: start from the outside-mount reference point created by the opening dimension plus 42mm.
• Run the tape from that same starting point to each vertical break where a T-post should sit.

For the right section of your corner window:

Begin your reading in the inner corner and stop to the centre point of each vertical break where a T-post should sit.