How to Measure for Blinds and Shades

What you need

Record every measurement in inches to the nearest sixteenth. Always write width first and height second — the whole industry reads it in that order, and a reversed pair is the single most common cause of a wrong-size shade.

• A steel tape measure — never a cloth or fabric tape, which stretches
• A step ladder for anything above head height
• A pencil and a sheet of paper, one line per window
• A second person for wide openings and sliding doors

Inside mount: width, height and depth

An inside mount sits the shade inside the window opening, showing the trim around it. It gives the cleanest, most built-in look, and it needs enough depth for the headrail or cassette.

• Width: measure the opening at the top, the middle and the bottom. Write all three down. The narrowest is what governs an inside mount.
• Height: measure at the left, the center and the right. Write all three down. For an inside mount the longest usually governs, so the shade reaches the sill everywhere.
• Depth: measure from the face of the glass to the front edge of the opening. This is what decides whether the product physically fits inside the window.
• Do not deduct anything yourself. Record the exact opening; the fabricator applies the correct deductions for the product.

Outside mount: covering the opening

An outside mount fixes the shade to the wall or the trim above the opening, so the shade covers the window rather than sitting in it. It is the answer for shallow openings, for out-of-square windows and for any room that needs to be dark.

• Width: measure the opening, then add overlap on each side — more overlap means less light escaping at the edges.
• Height: measure from where the headrail will be mounted down to where the shade should finish, whether that is the sill, the apron or the floor.
• Check there is a solid, flat mounting surface at the intended height, and that trim, crown moulding or a curtain rod will not interfere.

Window depth and mounting clearance

Depth is the measurement people forget, and it is the one that most often forces a change of plan. Different products need different depths: a slim roller needs the least, a cassette zebra shade needs more, and a dual shade system with two tubes needs the most.

Measure the clear depth — the space with nothing in it. A window with four inches of reveal but a crank handle two inches in has two inches of usable depth, not four.

Obstructions: handles, cranks, trim and sills

Anything that projects into the opening changes the measurement. Note each one, its position and how far it projects.

• Window handles and crank arms — very common on casement and awning windows
• Alarm contacts and sensors fitted to the frame
• Deep tile sills that sit proud of the opening
• Applied trim, mouldings and shutter hardware left from a previous installation
• Air-conditioning grilles and outlets directly below the window

Out-of-square and uneven openings

Older South Florida homes, renovated units and homes with replacement impact windows very often have openings that are not square. That is why you measure three widths and three heights rather than one of each.

If the three widths differ by more than a small amount, an inside mount will show a visibly tapering light gap at one side. Where that will bother you, an outside mount hides the discrepancy entirely.

Large windows and sliding glass doors

For a sliding door, measure the whole opening — frame to frame and head to floor — rather than each panel of glass. Then decide whether the opening is covered by one shade or by several matched shades, and where the splits should fall so the door you actually use stays accessible.

For tall windows, measure the drop at both sides; a long drop magnifies any difference. Note whether the shade will be mounted at the ceiling line or at the window head, because that decision changes the height measurement completely.

Ceiling mount considerations

Mounting to the ceiling, or to a soffit above the opening, gives a full-height look on a wall of glass and removes the light gap above the shade. It requires structure to fix into and enough clearance so the shade hangs clear of the window head, the frame and any curtain track already in place.

The most common measuring mistakes

• Writing height before width
• Measuring the glass instead of the opening
• Taking one width and one height instead of three of each
• Making your own deductions for the product
• Forgetting to measure the depth
• Ignoring a handle, crank or sill that projects into the opening
• Using a cloth tape, or measuring alone across a wide slider

When DIY measuring is enough — and when it is not

DIY measurements are useful for planning and preliminary estimates. Final measurements for custom-made window treatments should be verified professionally before production.

That is not a sales line — a custom shade is fabricated to your numbers, so an error is not adjustable afterwards. Our in-home measure is free across Miami-Dade, Broward and Palm Beach counties, and it also settles the questions a tape cannot answer: which mount suits the opening, whether the depth carries the product you want, and how a wide run should be split.

Frequently asked questions

Related services

• Blinds Installation
• Custom Blinds for Specialty Windows

More guides

• Inside Mount vs Outside Mount
• How to Choose Window Shades
• Window Treatments for Large Windows
• Window Shades for Sliding Glass Doors