How to Measure Your Windows for Custom Blinds and Shades

Measuring your own windows is a good habit even when a professional will do the final measure. It helps you plan, it gives you a realistic sense of the project, and it means you understand the numbers on your quote instead of taking them on faith. The method is simple once you know the two things that actually matter: whether the covering sits inside the window opening or over it, and how square the opening really is.

Grab a steel tape measure, not a cloth one, and write everything down in inches to a sixteenth where you can. A pencil and a scrap of paper beat trying to remember four numbers per window. Then decide, window by window, between an inside mount and an outside mount.

Inside mount or outside mount

An inside mount sits the blind or shade inside the window frame, giving a clean, built-in look that shows off the trim. It needs enough depth in the frame for the headrail to fit, and it needs an opening that is reasonably square. An outside mount fixes the covering to the wall or trim above the window, covering the whole opening and a little beyond. It hides an out-of-square frame, blocks more light around the edges, and works when the frame is too shallow for an inside mount.

Neither is better in the abstract. The right choice depends on the window, the look you want, and how much light you need to keep out. A lot of homes end up with a mix.

Measuring for an inside mount

Measure the width in three places: across the top of the opening, across the middle, and across the bottom. Windows are rarely perfect, so these numbers often differ. Write down the narrowest of the three, because the covering has to clear the tightest point. Then measure the height in three places as well, from the top of the opening to the sill on the left, the centre, and the right, and record the measurements the fabricator asks for. Finally, check the depth of the frame from the glass to the front edge, since that tells you whether the headrail will fit flush or need a spacer.

Do not round your numbers or shave a little off to be safe. A custom shop makes the deductions it needs for clearance. Your job is to report the opening exactly as it is.

Measuring for an outside mount

Outside mounts are more forgiving. Decide how much of the wall you want the covering to overlap on each side and above, usually a few inches, so light does not leak around the edges. Measure the full width you want the covering to span, then the full height from where the headrail will sit down to where you want the shade to end, whether that is the sill, the apron below it, or the floor for a tall window or a patio door. Make sure there is a solid surface to fasten into above the window.

Where St. Catharines windows get tricky

This is where a self-measure and a professional measure tend to part ways, and it is worth knowing before you order anything sight unseen. St. Catharines has a wide range of housing, from heritage homes in older areas like Old Glenridge and Port Dalhousie to post-war and newer subdivisions that grew as the city expanded. The older stock is where measuring gets interesting.

Character homes settle over decades, and their window openings are often out of square by more than you would guess from looking. A frame that appears fine to the eye can be a half inch wider at the bottom than the top. Older windows also come in shapes a standard measure does not cover well: arched tops, bay and bow configurations, and deep or shallow casings that change what will mount cleanly. Getting any of these wrong on a custom order is an expensive lesson.

Climate adds a subtle wrinkle too. Niagara runs a borderline humid continental climate, moderated by Lake Ontario and sheltered by the Niagara Escarpment, with lake-effect snow and frequent winter thaws. Wood frames in particular move a little as humidity swings through the seasons, so a snug inside mount measured on a damp August afternoon behaves differently in a dry January. A professional accounts for that; a rushed self-measure usually does not.

Bay, bow, and specialty windows

Bay and bow windows deserve their own note, because they are common in the region's older homes and they are the easiest to get wrong. A bay is a set of flat windows that meet at angles; a bow is a gentle curve of several windows. Each section is measured as its own window, and the angles where they meet decide whether the coverings can sit side by side without colliding when they are lowered or tilted. That is genuinely hard to judge with a tape alone, and it is the case we most often suggest leaving to the professional measure. Arched tops and windows that run to the floor follow the same logic: measure each element on its own and note how it relates to the ones beside it.

Label everything as you go. Note the room, the window, whether you measured for an inside or outside mount, and the width and height readings for each opening. When you sit down with samples later, that sheet turns a vague plan into a real conversation, and it keeps two similar windows in the same room from getting mixed up. It also gives whoever does the final measure a useful starting point.

Common measuring mistakes

The errors that cost the most are easy to name. Measuring only once across a window and assuming it is square. Using a cloth tape that stretches. Guessing the depth for an inside mount and finding the headrail sticks out. Forgetting to check for obstructions like handles, cranks, and alarm sensors that sit in the path of the covering. Ordering to a rounded number instead of the true measurement. Each of these turns a custom covering into a return, and custom orders are not easy to return.

Why the final measure is worth handing off

You can absolutely measure your own windows to plan and budget, and doing so makes the whole process clearer. When it comes to the order, though, the measurement that matters is the one the installer stands behind. During a free in-home consultation we measure every window with you, account for out-of-square openings and specialty shapes, and confirm the mount that suits each room. Because the measure is ours, the fit is our responsibility, not yours. If you would rather skip the tape and have it done right, you can book a measure for custom blinds and shades in St. Catharines and we handle the numbers.

Want the measuring done for you? Book a free in-home consultation with Budget Blinds of Niagara. We measure every window, bring samples to your home, and give you a written quote with options at more than one budget. Call (905) 650-3210 or request a consultation online. Locally owned and operated in the Niagara region, rated 5.0 on Google.