How to Measure Windows for Blinds

When buying blinds in Canada—or anywhere else—you’ll come across two main installation methods: Inside Mount and Outside Mount.

With an inside mount setup the blinds or shades are installed within the window frame. This approach provides a streamlined, built-in look that showcases the window’s existing trim. Depending on the fit of the blinds, inside mounts can let in more natural light around the edges (provided there is a gap). With an accurate measurement however, the amount of light "leakage" is minimal. 

When opting for an inside mount, a minimum window depth of around xxx cm (xxx inches) is typically required so that there is sufficient space to accommodate the roller shade head rail or blind hardware.

An outside mount places the blinds or shades on the wall or trim surrounding the window.

The hardware thus extends beyond the window frame. While an inside mount is generally preferred by most people, for it is the cleaner and more aesthetically pleasing solution there are also scenarios where an outside mount is more appropriate: In cases where windows window sides are not perfectly straight, or if a window has tiles that run up part of the window recess. This results in an uneven window width (with the window being narrower at the section where the tiles are installed) and is common with kitchen or bathroom windows. 

If this is the case you can either opt for inside mounting by taking the measurement of the shortest width and accepting larger side-gaps the for parts of the window where no tiles are fitted, or by opting for an outside mount window blind installation. 

An outside mount is also the only solution when a window frame is not deep enough to accommodate an inside mount.

Check Window Depth: 
Before you measure anything, confirm the inside depth of your window frame. Roller shades and blinds typically need between 1 to 2 inches (2,5 to 5cm) of depth to fit properly, though this can vary based on product specifications.

Measure the Width:

• Take three separate measurements for width—one across the top, one across the center, and one across the bottom of the window opening.
• Record the smallest of the three measurements (to account for any slight window frame irregularities).
• Round down to the nearest 1/8 of an inch (0.32cm) if necessary.
  
  

Measure the Height (Length):

• Measure the vertical distance from the top of the inside opening to the window sill in three different spots: left, center, and right.
• Note the largest of these three measurements.
• Again, round to the nearest 1/8 of an inch (0.32cm) if you encounter slight variations.
  
  

Record Your Dimensions Clearly:

• Label each window with a unique code or name (e.g., “Living Room Window 1”) and keep track of your measurements in a table or spreadsheet.
• Always write “width x height” (W x H) in that order to avoid confusion.
  
  

Consider Any Obstacles:

• Check for window cranks, handles, or protruding hardware that could interfere with how the blinds operate.
• If necessary, measure around these obstacles or consider a different mounting style if space is too tight.

An outside mount can help accommodate for shallow window frames. Here’s how to measure:

Determine Desired Coverage:
Decide how far beyond the window opening you’d like the blinds or shades to extend. Typically, adding 2–3 inches (5 - 7.6cm) beyond the window’s width on each side provides better privacy and light control.

Measure the Width:

• Start from where you’d like the left edge of the blinds to be to where you’d like the right edge to end.
• For roller shades or blinds, it’s common to extend coverage above the window by at least 2–3 inches (5 - 7.6cm) as well.

Measure the Height (Length):

• Measure from the top of your intended mount (often 2–3 inches (5 - 7.6cm) above the window frame) down to where you want the bottom of the blinds to fall.
• For windows with a window sill that sticks out, measure until just below the sill or slightly beyond, depending on your preference.
  
  

Check for Obstacles and Hardware Placement:

• Ensure you have enough flat wall surface or trim area for brackets.
• Note any outlets, light switches, or molding details that might affect placement.
  
  

Record Your Dimensions:

• As with inside mount instructions, keep your notes consistent with W x H.
• Label these as “Outside Mount” so you don’t confuse them with inside mount measurements if you’re comparing both options.

While measuring windows is a straightforward task and virtually none of our customers manage to get it wrong, it is of course possible to make mistakes. So to caution you against these, here are potential sources for measurement errors:

1. Not Using a Steel Tape Measure: Cloth tapes can stretch, producing inaccurate results.
   
   
2. Not Measuring Each Window Individually: Never assume two windows are exactly the same size—even if they look identical, slight variations are common. And with custom size shades and blinds accuracy is key.
   
   
3. Not Keeping the Tape Level: Tilting the tape can add fractions of an inch. If you suspect your frame is crooked, measure in three places (top, middle, bottom) for inside mounts.
   
   
4. Not Rounding Down for Inside Mount Widths: If in doubt, pick the smallest measurement to ensure the blinds will fit within the frame.
   
   
5. Not Round Up for Outside Mounts: For outside mounts the opposite is true: choose a slightly larger size if you are in between measurements. This improves coverage and light blockage.
   
   
6. Not Noting the Location of Window Handles and Cranks: Interference from handles can affect how roller shades roll up and down. You might need a spacer or to opt for an outside mount if the handles protrude significantly.

Not every window is a perfect rectangle. Many Canadian homes feature bay windows, corner windows, arch-topped openings, or other unique shapes that add architectural interest but can complicate the measuring process. Here’s how to approach these scenarios:

Break It Down into Segments:

• For bay windows, treat each panel of glass as a separate “mini-window.” Measure each one using the standard inside or outside mount instructions.
• In corner window setups, measure each window section independently, taking extra care around the corner area to ensure accurate fit.

Account for Angles and Overlaps:

• Some bay windows have interior angles that might reduce the available space for mounting hardware. Verify the distance from each corner to the next to confirm hardware can fit, particularly if you plan an inside mount.
• If you’re using outside mounts, decide how far you want the blinds to overlap each window edge so the entire bay appears cohesive.

Consider Specialty Brackets or Custom Solutions:

• For highly angled or arched windows, you might need specialty brackets or curved track systems.
• Contact us to discuss the best options given your window shape.