How to Measure Windows for Blinds: Complete Canadian Guide

Why accurate measurements matter

Getting your window measurements wrong is the number one reason blinds don't fit properly. Even a 1/4-inch error can mean visible light gaps, crooked hanging, or blinds that won't operate at all. Custom blinds are built to your exact specs and can't be returned for sizing errors.

At Blinds Planet, we offer free professional measurement with every order. But whether you're getting a head start before your consultation or ordering standard sizes, this guide covers everything you need to know.

Tools you'll need

Before you start, grab these items:

- Steel tape measure (cloth tapes stretch and are inaccurate)

- Pencil and paper or a phone to record measurements

- Step stool or ladder for high windows

- Level (optional but helpful for checking window squareness)

Pro tip: Always use a steel tape measure. Cloth and plastic tapes can stretch by 1/8 to 1/4 inch, which is enough to ruin a custom blind order.

Inside mount vs outside mount: which should you choose?

This is the first decision you need to make, and it affects every measurement you take.

Inside mount

The blind sits inside the window frame for a clean, built-in look.

Choose inside mount when:

Minimum depth requirements:

Outside mount

The blind mounts on the wall or trim above the window, overlapping the frame.

Choose outside mount when:

How to measure for inside mount

Step 1: Measure the width

Measure the width at three points:

1. Top of the window opening (inside the frame)

2. Middle of the window opening

3. Bottom of the window opening

Record the narrowest measurement. This ensures the blind will fit at the tightest point without binding.

Measure to the nearest 1/8 inch. Do not round up.

Step 2: Measure the height

Measure the height at three points:

1. Left side of the window opening

2. Centre of the window opening

3. Right side of the window opening

Record the longest measurement. This makes sure the blind covers the full window height.

Step 3: Measure the depth

Measure from the front edge of the window frame to the back (where the glass is). This tells you whether your chosen blind type will fit inside the frame.

A note for Canadian homes: Many older Toronto homes and GTA properties have frames that aren't square due to settling. If your width measurements differ by more than 1/4 inch across the three points, go with outside mount instead.

How to measure for outside mount

Step 1: Measure the width

Decide how far past the window frame you want the blind to extend on each side. We recommend:

- Standard: 2 inches of overlap on each side (total width = window width + 4 inches)

- Blackout: 3 inches of overlap on each side for maximum light blocking

- Decorative: 4+ inches for a dramatic, statement look

Measure the total width you want the blind to cover.

Step 2: Measure the height

Decide where you want the blind to start (above the window) and end (below the window sill or at the sill).

Recommended overlap:

- Top: Mount 3-4 inches above the window frame. This stops light from leaking over the top and makes the window look taller.

- Bottom: Extend 1-2 inches below the window sill, or to the floor for full-length coverage.

Step 3: Mark your mounting points

Use a pencil to mark where the brackets will go. Check with a level to ensure the marks are even.

Room-by-room measurement tips

Condos and high-rise units (common in Toronto and Mississauga)

Floor-to-ceiling windows are standard in GTA condos. Special considerations:

Patio and sliding doors

Bay windows

Arched and specialty windows

These need a template. Use a large piece of cardboard or paper to trace the exact window shape. Our installation team handles these during the free in-home consultation.

Common measurement mistakes

Mistake 1: Using a cloth tape measure

Cloth tapes stretch over time. Always use a rigid steel tape for accuracy.

Mistake 2: Rounding to the nearest inch

Custom blinds are built to 1/8-inch precision. Rounding up by even 1/2 inch means the blind won't fit inside the frame.

Mistake 3: Measuring only once

Always measure at three points for both width and height. Windows are rarely perfectly square, especially in older GTA homes.

Mistake 4: Forgetting obstructions

Check for handles, cranks, locks, and trim that could get in the way. Measure the clear space available, not just the frame dimensions.

Mistake 5: Not checking the depth

If you want inside mount but your frame is too shallow, the blind will stick out past the frame. Check depth before committing to inside mount.

Measurement checklist

Use this checklist for each window:

When to call a professional

Measuring is straightforward for standard rectangular windows, but some situations really do call for professional help:

- Specialty shapes (arches, circles, triangles)

- Very large windows (over 96 inches wide)

- Multiple windows that need to align precisely

- Motorized installations that require electrical planning

- Bay windows with complex angles

Blinds Planet offers free professional measurement across the Greater Toronto Area, including Toronto, Mississauga, Brampton, Vaughan, Oakville, and Richmond Hill. Our team measures windows across the GTA every day and catches issues that DIY measurements commonly miss.

Ready to get started?

Whether you measure yourself or use our free measurement service, getting the numbers right is what makes the difference between blinds that fit and blinds that don't.

Contact Blinds Planet at (416) 890-4554 or request a free quote online. We'll confirm your measurements during the in-home consultation before placing any order.