Why Accurate Window Measurements Matter
Measuring your windows correctly is the single most important step before ordering new blinds. A measurement that is off by even one eighth of an inch can leave gaps that let in unwanted light, cause the blind to rub against the frame, or prevent it from operating smoothly. According to the Window Coverings Manufacturers Association (WCMA), improper measuring is the leading cause of returns and exchanges in the window treatment industry. Taking the time to measure properly the first time saves you money, frustration, and weeks of waiting for replacement blinds.
At Wildrose Blinds, we see measurement mistakes from homeowners across Calgary, Okotoks, and the wider Foothills region every week. Most of these errors come down to a handful of common habits, like measuring only one spot instead of three, using a flexible tape measure, or measuring the old blinds instead of the window opening. This guide walks you through the correct process step by step so you can order with confidence or simply be better prepared for your free in-home consultation.
Tools You Need Before You Start
Gather these supplies before you measure a single window:
- A steel tape measure at least 25 feet long
- A pencil and a notepad for recording each measurement
- A step ladder for taller windows
Avoid using fabric measuring tapes, rulers, or your phone. Steel tape measures stay rigid inside the window frame and give you readings accurate to the nearest one eighth of an inch. For a detailed overview of window treatment standards and best practices, the Consumer Reports window treatments guide offers reliable guidance on choosing and measuring coverings. This level of precision matters for every type of blind, from roller shades and cellular blinds to plantation shutters. For more on how window treatments affect your home comfort, see our energy-efficient window coverings guide for Alberta winters.
Inside Mount vs Outside Mount
Before you pick up your tape measure, you need to decide whether your blinds will mount inside the window frame or outside it on the wall or trim. This decision changes how you measure and how much overlap you need.
When to Choose an Inside Mount
An inside mount fits the blind within the window frame. This option works well when your window frame has enough depth to accommodate the blind hardware. Most standard blinds need between one and three quarters of an inch and two and three quarters of an inch of depth, depending on the product type. Inside mounts give your windows a clean, built-in look and preserve the look of decorative trim around the opening.
When to Choose an Outside Mount
An outside mount places the blind on the wall or trim above the window opening. This is the better choice when your window frame is too shallow for an inside mount, when the window is not perfectly square, or when you want maximum light blockage. Blackout roller shades are a popular choice for bedrooms where light control is essential. Outside mounts add two to three inches of overlap on each side, which helps cover gaps and reduce light bleed around the edges.
How to Measure for an Inside Mount
Step 1: Measure the Width in Three Places
Measure the width at the top of the window opening, then at the middle, then at the bottom. Windows are almost never perfectly square, and drywall or trim can create slight variations. Write down each measurement to the nearest one eighth of an inch. Use the narrowest of the three widths when you place your order. This ensures the blind fits without binding or rubbing against the frame.
Step 2: Measure the Height in Three Places
Measure the height on the left side, in the center, and on the right side. For the height, use the longest of the three measurements. The blind manufacturer will make a small deduction from this number to allow clearance for the hardware, so you want to give them the tallest measurement to avoid leaving a gap at the bottom.
Step 3: Check the Window Depth
Measure from the front edge of the window frame back to the glass. Take this measurement at the left, center, and right, and use the shallowest depth. Compare this number to the minimum depth required for the blind type you plan to order. If the frame is not deep enough, you will need to use an outside mount instead.
Step 4: Check for Obstructions
Look inside the window frame for anything that might block the blind. Window cranks, locks, handles, and security sensors can all interfere with an inside mount. If an obstruction sits more than half an inch inside the frame, note its position and measurement. You may need a shallow-mount bracket or an outside mount to clear it.
How to Measure for an Outside Mount
Step 1: Measure the Total Width with Overlap
Measure the full width of the window opening from one side to the other. Then add at least two inches on each side for a total of four inches of overlap. This overlap blocks light from leaking in at the edges and gives the blind a proportional, finished appearance. For wider windows, you can increase the overlap to three inches per side.
Step 2: Measure the Total Height with Overlap
Decide where the top of the blind will sit. For most installations, the headrail mounts at least three inches above the window opening. Measure from that point down to the windowsill. If you want the blind to extend below the sill for extra coverage, add one to three inches to the bottom. Record the total height to the nearest one eighth of an inch.
Step 3: Confirm the Mounting Surface
Check that the wall or trim above the window can support the blind brackets. You need at least two inches of flat, solid surface for the bracket mounting screws. If you are mounting into drywall without a stud behind it, plan to use wall anchors rated for the weight of your blinds.
Measuring Special Window Types
Bay and Bow Windows
Bay and bow windows require individual measurements for each section. Measure each flat section as a separate window, and also measure the angles between sections with an angle finder or a protractor. For these windows, professional measuring is strongly recommended because small angle errors compound across multiple panels and can leave noticeable gaps.
Sliding Glass Doors
For patio doors, measure the width of the glass area and add overlap on each side. Vertical blinds and panel track blinds are common choices. You might also consider automated window blinds for hands-free operation of large patio door coverings for sliding doors. Measure the height from the mounting point above the door frame to the floor, and add at least one inch of overlap at the bottom so the blind clears the floor track.
Arched and Specialty Windows
Arched windows need a template. Trace the curve of the arch onto a piece of cardboard or paper, mark the width and height, and send the template to the manufacturer with your order. Most blind companies, including Wildrose Blinds, can fabricate custom arch treatments from a template.
Common Measuring Mistakes to Avoid
Measuring Only One Point
The most frequent mistake is measuring the width or height in just one spot. Even new homes have windows that vary by a quarter inch or more between the top and bottom. Always measure in three places and use the correct extreme: narrowest width, longest height for inside mounts.
Measuring the Old Blinds Instead of the Window
Your existing blinds may have been cut to fit an imprecise measurement or may have shifted over years of use. Always measure the window opening itself, not the blinds that are currently hanging in it.
Using a Flexible Tape Measure
Fabric or flexible tape measures bend inside narrow frames and give inaccurate readings. Use a rigid steel tape measure for every measurement.
Forgetting to Account for Handles and Locks
Window handles and locks protrude into the frame. If you do not account for them, the blind will hit the hardware when you try to lower it. Either plan for an outside mount or choose a blind with enough depth clearance.
Not Labelling Each Window
If you are measuring multiple windows, label each measurement clearly. Write down the room, the window position, and whether it is an inside or outside mount. Mixing up measurements is a surprisingly common way to end up with blinds that do not fit.
When to Call a Professional
Measuring is straightforward for standard rectangular windows with clear frames. But some situations call for professional help. If your home has bay windows, arched windows, or windows that are significantly out of square, a professional measurement ensures accuracy and saves you from costly mistakes. Professional installers also account for ceiling height, wall irregularities, and trim details that DIY measurements often miss.
At Wildrose Blinds, every in-home consultation includes professional measuring at no charge. We bring samples directly to your home in Calgary, Okotoks, and across the Foothills region so you can see how different materials and styles look with your existing decor. Our team handles the entire process, from precise measurements to expert installation, so you never have to worry about whether your blinds will fit.
Ready to Get Started?
Accurate measuring is the foundation of a great-looking window treatment installation. Whether you plan to measure and order yourself or prefer hands-on guidance, Wildrose Blinds is here to help. Explore our full range of window blind types to find the right style for your space, or book a free consultation and let our team handle the measuring for you. Call us at +1 587 332 5566 to schedule your appointment today. For more tips on choosing the right products for your Calgary home, check out our guide to blinds in Okotoks and Southern Alberta.
