Getting the measurement right is the entire ballgame with custom blinds. A shade that is a quarter inch too wide jams against the window frame. A shade that is a quarter inch too narrow leaves a visible light gap. A shade ordered at the wrong height hangs crooked or drags on the sill. There is no margin for error when your product is cut to order.
Here is the process our installers use every day across Brampton, Toronto, Mississauga, and the rest of Southern Ontario. If you follow it carefully, your measurements will be accurate enough to order from. If you skip steps or guess, you will end up paying to replace a shade that does not fit.
Before You Measure: What You Need
- A steel tape measure. Cloth or plastic tapes stretch and give bad numbers. Use metal.
- Pen and paper or notes on your phone. Write every measurement down. Do not try to remember them.
- A step stool for any window over eye level. Do not measure tall windows standing on your toes.
- A pencil for marking outside-mount boundaries on the wall.
Measure in the same unit throughout. If you start in inches, stay in inches. Do not mix metric and imperial on the same order. Converting between units at the end is where most mistakes happen.
Step One: Decide Inside or Outside Mount
Before any numbers get written down, pick your mount type. This determines how you measure.
Inside Mount
The blind sits inside the window recess, flush with the frame. This is the cleaner, more built-in look and it is the standard choice for newer homes across Brampton, Vaughan, and Markham where the trim is square and deep. Inside mount requires at least 2 inches of depth inside the frame for most roller and zebra blinds. Cellular and Roman shades may need more. Check the spec sheet for the specific product before ordering.
Outside Mount
The blind mounts on the wall or trim above the window, covering the frame entirely. Use outside mount when your window depth is too shallow for an inside mount, when the frame is uneven or damaged, or when you want maximum light blocking (outside mount overlaps the frame on both sides, so there is no light gap).
Step Two: Measure for Inside Mount
Width
- Measure across the inside of the frame at the top of the window.
- Measure across the inside of the frame at the middle.
- Measure across the inside of the frame at the bottom.
- Record the narrowest of the three. Round down to the nearest 1/8 inch or 1 mm.
Windows are rarely perfectly square. The three measurements will not match exactly. Using the narrowest width ensures your blind will slide into the opening without jamming.
Height
- Measure from the top of the recess to the sill on the left side.
- Repeat in the centre.
- Repeat on the right.
- Record the longest of the three if you want the blind to reach the sill. Record the shortest if you want the blind to stop above the sill.
Depth
Measure the depth of the window recess from the glass to the front edge of the frame. Compare this to the minimum depth requirement listed on the product you are ordering. If your depth is insufficient, either switch to an outside mount or choose a slimmer product.
Rule of thumb: measure, then measure again
Always measure every window twice, even if you think you nailed it the first time. A second measurement takes 30 seconds and catches transpositions (reading 36 as 63 is the single most common mistake).
Step Three: Measure for Outside Mount
Width
Measure the width of the window frame itself, then add at least 4 inches total (2 inches on each side) for proper light coverage. For high-privacy applications in bedrooms or street-facing rooms, add 6 inches total (3 inches on each side). Wider overlap means less light leakage at the edges.
Height
Measure from where you want the top of the shade to sit down to where you want the bottom of the shade to end. This is typically 3 to 4 inches above the top of the window frame and 2 to 3 inches below the sill, but it is purely a visual choice. Mark both positions on the wall with a pencil before you measure so you are recording a real number, not an estimate.
Skip the tape measure. We'll do it for you.
Our consultants visit your home across Brampton, Toronto, Mississauga, Oakville, Hamilton, and 7 other Southern Ontario cities. Exact measurements, written quote, no charge.
Book a Free MeasureThe Five Most Common Measurement Mistakes
1. Measuring the curtain or existing blind instead of the window
The existing blind might have been cut wrong by a previous owner. Always measure the raw window or recess, not what is currently hanging in it.
2. Forgetting to account for window cranks or handles
Crank-out windows and tilt-and-turn windows need clearance for the handle. Measure with the handle extended if it will interfere with the shade.
3. Ordering "window size" when the manufacturer expects "finished size"
Some manufacturers build a deduction into the order (they want you to send the window opening and they shrink it). Others expect you to send the exact shade size you want (no deduction). Confirm this in writing before you order. This is the single most expensive mistake people make with online-only custom blind sites.
4. Mixing imperial and metric
Stay in one unit through the whole process. A 40 mm conversion error on a 1.8 m window is barely visible on paper. It looks terrible when the shade arrives and hangs an inch too short.
5. Not checking for level and square
Many older homes in Toronto, Oshawa, and Hamilton have windows that are visibly out of square from house settling. If the top of your window is 36 inches wide and the bottom is 35.5 inches wide, that is a real half-inch difference you need to account for. Use the narrowest number.
When to Get a Professional Measure
For standard, straightforward rectangular windows in a newer home, a careful homeowner can measure their own blinds accurately. For anything beyond that, paying a professional to measure is cheaper than replacing a mis-cut shade.
You should get a professional measure if:
- Your windows are arched, angled, or an unusual shape. See our arched blinds guide.
- You are ordering motorized blinds, which have tighter tolerances and require power planning.
- The window is over 72 inches wide or 96 inches tall.
- You have multiple windows to cover and want consistent headrail heights.
- You are installing plantation shutters, which have zero error tolerance.
- The home is older and the windows are visibly out of square.
Luna's free in-home consultation includes a full professional measure of every window in your home. We bring the full sample collection, measure every opening, and leave you with a written quote the same day. If you are in Brampton, Mississauga, Toronto, Vaughan, or any of our 12 service cities, it is genuinely faster and more accurate than measuring yourself.
