Sunny Shutter Support Centre
How to Measure Windows for Blinds & Shades
Measure the opening in multiple places, record exact dimensions as width x height and identify the mount type before ordering. For inside mounts, use the smallest width and the smallest height.
The short answer
Measure the opening. Do not guess the product deduction.
Use a metal tape, measure in at least three places and submit exact opening dimensions for an inside mount. Sunny Shutter applies the appropriate production deduction for the selected system.
Sunny Shutter inside-mount rule: measure the width at the top, middle and bottom and use the smallest result. Measure the height at the left, centre and right and use the smallest result. Record the exact opening size and do not take your own factory deduction.
Choose before measuring
Inside mount or outside mount?
Mount type determines which edges you measure, how the finished treatment looks and how much edge coverage it provides.
Measure the opening
The window covering sits inside the recess for a clean, built-in look. The opening needs enough unobstructed depth for the selected headrail, cassette or shutter frame.
- Measure exact inside edges
- Use the smallest readings
- Check the shallowest depth
- Do not deduct clearance
Measure the coverage
The window covering mounts to the trim or wall and covers the opening. It works well when recess depth is limited or additional privacy and light coverage is preferred.
- Measure finished coverage
- Confirm flat mounting space
- Account for trim and sill
- Record total width and height
Choose inside mount when the recess is deep, square and unobstructed. Choose outside mount when depth is limited, the opening is uneven or greater coverage is more important.
Inside mount
Measure the exact opening in three places.
The window recess, not the glass, is the measurement reference. Measure at the points where the treatment will actually sit and record every result before selecting the final width and height.
Record exact opening dimensions. Do not subtract a clearance allowance yourself. Sunny Shutter applies the appropriate production deduction for the selected product and mount.
Measure width at top, middle and bottom.
Measure from the inside edge on the left to the inside edge on the right. Record W1, W2 and W3, then use the smallest value.
Measure height at left, centre and right.
Measure from the top inside edge to the sill or bottom inside edge. Record H1, H2 and H3, then use the smallest value.
Measure unobstructed depth.
Measure from the front edge of the recess to the first obstruction near the mounting area. Check handles, locks, screens and inward-tilting sashes.
Check squareness and diagonals.
Measure corner to opposite corner in both directions. If the diagonals differ noticeably, around 1/4 in or more, send photos and ask whether an outside mount is safer.
Record control and room details.
Write the room name, mount type, preferred control or motor side, product type and any obstruction notes.
Repeat every number before ordering.
Read the tape again, confirm width x height order and make sure every fraction and window label is legible.
Outside mount
Measure the finished coverage - not only the glass.
For an outside mount, the ordered width and height describe the total product size or coverage area. Plan overlap for privacy and light control while preserving enough flat surface for the brackets.
Choose the mounting line.
Confirm whether the brackets will fasten to the trim or wall. Many cassette systems need roughly 2.5 in of flat surface, but the required space varies by product.
Set the finished width.
With trim, a common reference is outer trim edge to outer trim edge. Without trim, mark the desired overlap on both sides and measure between those marks.
Set the finished height.
Measure from the selected top edge to the sill or desired bottom edge. If the sill protrudes, stop at the sill; without a sill, include the intended bottom overlap.
Check surrounding clearance.
Confirm the cassette will not hit the ceiling, side wall, crown moulding, door lever, radiator or furniture during installation and operation.
Where space allows, up to 4 in total added width and approximately 4 in total added height can improve privacy and reduce light gaps. Final overlap depends on trim, sill and product.
Outside-mount products are generally ordered at the finished width and height you specify. Roller, solar and sheer systems can have internal fabric or hardware deductions; Sunny confirms these by product.
Do not add overlap twice. If you measure from the outer edge of existing trim, the trim may already provide the intended coverage. Record exactly which edges you used and include a straight-on photo.
Product-specific checks
One inside-mount rule. A few product details.
The smallest measurements determine the order size. Product type then affects depth, clearance and operating details, not the basic three-point rule.
Special windows
Some openings need more than width and height.
Send clear photos and ask before ordering when angles, multiple sections, doors, arches or obstructions affect the fit.
Bay and bow windows
Record each section, mullion location, approximate angles and projection. Do not divide a total width into equal shades without planning control clearance and gaps.
French and patio doors
Measure the desired coverage and note handle projection, glass trim, door swing and available mounting surface above the glass.
Multiple shades in one opening
Record total opening width, each mullion centre and the preferred shade split. Motor and control sides affect the meeting gaps.
Arched or non-rectangular windows
A simple width x height is not enough. Templates, detailed dimensions or professional measurement may be required.
Very large or high windows
Do not lean or improvise from an unsafe ladder. Large products also require hardware, access and lifting planning.
Record each opening
Make every measurement traceable.
Use one line per window and include enough information for someone else to understand exactly what was measured. Straight-on and side-angle photos help our team review depth, trim and obstructions during your consultation.
Window Measuring Worksheet & Guide
A practical printable reference you can keep beside you while measuring.
Free in-home consultation
Prefer us to measure?
For qualifying projects in Toronto and the GTA, Sunny Shutter can bring samples to your home, confirm the mount type, measure each opening and plan product-specific clearance before the order is finalized.
Sunny Shutter Inc.
690 Progress Avenue, Unit 7, Scarborough, ON
647-857-8669 / sales@sunnyshutter.ca
Recommended for shutters, bay windows, multiple aligned shades, very large windows and motorized systems.
After speaking with our team, share clearly labelled dimensions and photos so questions can be identified before production.
Custom-sized products depend on the confirmed dimensions. Stop and ask whenever the measurement reference is uncertain.
Measurement FAQ
Answers before you order.
The safest rule is to record exact, clearly labelled measurements and let the selected product determine the manufacturing deduction.
Do I deduct anything for inside-mount blinds?
No. Record the exact opening dimensions using the correct three-point rule. Sunny Shutter applies the product-specific production deduction. Taking your own deduction can make the finished product too narrow or short.
Which width measurement should I use?
For an inside mount, measure top, middle and bottom and use the smallest width. For an outside mount, record the total finished coverage width you want to order.
Which height measurement should I use?
For an inside mount, measure the height at the left, centre and right and use the smallest result for blinds, shades and shutters.
Should I measure to 1/8 inch or 1/16 inch?
Use a metal tape and record at least to the nearest 1/8 inch. If you can reliably read 1/16 inch, record the more precise fraction. Never round to the nearest whole inch.
How do I measure window depth?
Measure from the front inside edge of the recess to the first obstruction near the intended mounting area. Check several points and record the shallowest usable depth, including handles, locks, screens and tilt-in sash clearance.
How much overlap should an outside mount have?
A common starting point is about 2 inches per side and additional coverage above and below where space allows. Trim, sill, cassette size and desired light control can change the final overlap.
Can I measure a bay window myself?
You can record preliminary segment widths, mullion locations, approximate angles and photos, but the final layout must account for headrail depth, controls and meeting gaps. Professional measurement is recommended.
Can I share photos with my measurements?
Yes. After contacting our team, include a straight-on photo, a side-angle photo and close-ups of handles, locks, trim or other obstructions. Label the photos with the same room and window numbers used on the worksheet.
