How to Measure Windows for Blinds

First, you’ll need to decide whether you want inside mount or outside mount blinds. Inside mount blinds, as the name suggests, mount inside your window frame, while outside mount blinds mount outside or over the window frame.

Next, check the casing depth. If it is less than 2 inches, an outside mount is required. Also check the squareness. Measure your window casing diagonally in two places. If the two diagonal dimensions are not equal, an outside mount is recommended for optimal function and aesthetics.

Inside mount blinds will give you the cleanest look overall, while outside mount blinds offer more variety, as the window frame size doesn’t matter when choosing them. They’re also a great choice if you’ve got obstructions inside the frame, such as window openers.

Shades and Horizontal Blinds

To measure accurately, use a steel tape measure and round to the nearest 1/8th-inch.  Measure the depth of your window frame to ensure you’ve got enough space for an inside mount. To measure for inside mount horizontal blinds and shades, you’ll need to take six measurements – 3 for the width and 3 for the height.

Measure in three spots for height - one on the left, then the middle and then the right side. Record the shortest height for roller shades. For all other shades and horizontal blinds, record the longest height.

Then measure three times for the width - across the top, middle and then bottom of the frame. Record the narrowest width. For roller shades, only measure the width at the top of each window.

Vertical Blinds

Measure the width of your window opening at the top of your window. Next, measure the height at the left, centre and right of your window, whichever is the shortest measurement is the number to go with.These measurements along with your window depth will give you the exact measurements for your inside mounted window covering.

Shades and Horizontal Blinds

Remember to use a steel tape measure and round to the nearest 1/8^th-inch. Measuring for outside mount window coverings is a bit easier. First, you’ll need to determine the headrail location, which typically sits 1 ½ - 3 inches above the window. Then measure the height and width of your window frame to the outer edges. If you’ve got trim, measure to the outside of your trim. If your window has no trim around it, consider adding 3-inches to your width measurement, which will allow your blinds to extend past the window a bit farther and block more light.

Vertical Blinds

Be sure that you have enough flat surface for the mounting hardware. If your window has no trim, to keep light out and add privacy, add at least 4 inches on each side of your window.

Then determine the height of the blinds you need. If you have a protruding windowsill, measure 3 inches starting at the sill and going upward, past the top of the window opening so you have enough room for hardware. If you do not have a protruding windowsill, start your measurement below the sill by about 2 inches and then measure 3 inches upward beyond the window opening.