How to measure windows for blinds
Accurate measurements are the difference between blinds that fit cleanly and blinds that rub, gap or hang crooked. Here is the method, the tools and the pitfalls, whether you measure yourself or not.
Measuring for blinds is not difficult, but a few millimetres of error is enough for a blind to rub on the frame, leave light gaps or overhang the window. This guide covers how to measure windows for blinds, which mount to choose and when it makes sense to let an advisor do it.
Step 1: choose an inside or outside mount
Decide where the blind will be fixed before you pick up the tape. It changes how you measure.
Inside mount
The blind sits within the window recess. The look is tidy and the trim stays visible. You need:
- enough recess depth for the headrail or mechanism (this varies by blind type);
- a frame that is reasonably square;
- clear space around cranks, handles or trim.
Outside mount
The blind is fixed above or outside the frame, on the wall, trim or ceiling. You measure the area to be covered and add an overlap on each side. It is often the better option when:
- the recess is too shallow;
- you want to limit light leaking around the edges;
- you want the window to look wider or taller;
- the frame is uneven.
Step 2: gather your tools
- a rigid steel measuring tape (not a soft tape);
- a pencil and notebook, or one sheet per window;
- a level, to spot a frame that is out of square;
- a stable stepladder for tall windows.
Label each window (for example “living room 1”, “bedroom 2”) and keep the same labels on your sketch and your notes.
Step 3: take the measurements
Follow the same sequence each time:
- Measure the width at three points: top, middle and bottom of the opening.
- Measure the height at three points: left, centre and right.
- For an inside mount, record the smallest figure in each set. The blind has to fit the tightest point.
- Measure the depth of the recess, from the glass to the front edge of the frame.
- Note obstacles: handles, cranks, heating, outlets, trim.
- For an outside mount, measure the area to cover and plan an overlap on each side and above. Your advisor can tell you the right allowance for the product.
Measure in inches, to the nearest 1/8 inch. Do not subtract “a bit for clearance” yourself: the necessary clearances are handled in production, depending on the product.
What to record for each window
| Item | Where to take it | Why it matters |
|---|---|---|
| Width (top, middle, bottom) | Between the sides of the recess | The smallest figure sets the fit for an inside mount |
| Height (left, centre, right) | From the top of the opening to the sill | Avoids a blind that is too short or that hits the sill |
| Depth | From the glass to the front edge of the frame | Confirms whether an inside mount is possible |
| Mount type | Your choice | Changes how dimensions are calculated |
| Obstacles | Handles, cranks, radiators | May call for an outside mount |
| Room and use | Bedroom, kitchen, office | Guides the choice of fabric or mechanism |
Common mistakes
- Measuring only once. A frame that looks straight often varies by a few millimetres from one point to another.
- Using a soft tape. It sags and skews readings on wide windows.
- Forgetting depth. If a blind will not fit in the recess, it has to go on the wall instead.
- Rounding down “to be safe”. You end up with a blind that is too narrow and lets light slip through the gaps.
- Ignoring handles and cranks. They can block the blind or stop you turning the crank.
- Mixing up windows. Without labels, it gets confusing fast once you have more than two openings.
A few time-saving tips
- Measure all the windows in a room on the same day, with the same tape.
- Measure twice: if both sets agree, your readings are probably right.
- Take a photo of each window, with the tape in place for the depth.
- Note which way the window opens and whether there is a ledge or caulking.
- Decide which side you want the control (cord or bead chain) on, left or right.
Special cases: sliding doors and large windows
For a sliding patio door, measure the full width of the opening and the height down to the floor, and allow for the handle and space to walk through. Wide spans are easy to misread with a tape, and a small error shows more. This is where professional measuring is especially reassuring.
When to have an advisor measure
You can measure yourself to get a feel for sizes or to prepare a quote request. For production, though, it is better to have the dimensions confirmed, especially when:
- windows are large, corner units or an unusual shape;
- your three measurements do not agree;
- you are torn between an inside and outside mount;
- you are ordering for the whole house.
On request, an advisor from Stores d’Aujourd’hui comes to measure each window to the 1/8 inch, and this is included in the quote. Our blinds are made in our Gatineau workshop and installed by us.
What comes after measuring?
Once you have your dimensions, the next step is choosing the product. For a comparison of two popular styles, read our guide to Roman shades vs roller shades, or browse our solar, blackout and translucent roller shades and vertical blinds.
Ready for the next step? Request a free quote or visit our showroom at 865 boulevard Maloney Est, Gatineau.
What we get asked most
Should I choose an inside mount or an outside mount?
An inside mount sits within the window recess for a clean, tailored look, but it needs enough depth and a reasonably square frame. An outside mount goes on the wall or trim, and suits shallow recesses, stronger light blocking at the sides, or making a window look larger.
Do I only need to measure the width once?
No. Windows and recesses are rarely perfectly square. Measure the width at the top, middle and bottom, and the height at the left, centre and right. For an inside mount, you generally use the smallest figure in each set.
What tools do I need?
A rigid steel measuring tape, a pencil and paper are enough. Avoid a soft sewing tape, which sags and distorts. A level helps you spot a frame that is out of square. Record every measurement in inches, to the nearest 1/8 inch.
Can you come and measure my windows?
Yes. On request, an advisor comes to measure each window to the 1/8 inch, and this measuring visit is included in the quote. You get confirmed dimensions before anything is made.
How do I measure a sliding patio door or a large window?
Measure the full width of the opening and the height down to the floor, and note the handle and the clearance needed to use the door. For these large formats, having an advisor take the measurements is often the safest choice.
What if my three measurements are all different?
That is common, especially in older homes. Write down all three without rounding them yourself and share them with your advisor. They can recommend the mount that works best, often an outside mount, rather than forcing a blind into an uneven recess.
