Window blinds are a favorite among homeowners who want to add a little flair to their space. However, choosing the correct size isn't always second nature. If you want to learn how to measure your windows for blinds, continue reading this guide for easy-to-follow instructions.

Before You Begin

In order to purchase well-fitted blinds, you will need to measure your windows to obtain the correct dimensions. Start off with these tips and tricks to ensure you take all the measurements correctly.

• Only use a steel measuring tape. Any other tape measure might move, slip, or give inaccurate readings.
• Measure in inches not feet for the most precise measurements.
• Measure width from left to right and length from top to bottom.
• Always measure to the nearest 1/8". If your measurement falls on a 1/16" mark, round to the nearest 1/8". Do not round down or round up to a half or whole inch.
• Blind measurements are written in a specific order – width first then height. Make sure to mark your width and height measurements clearly to prevent accidentally transposing these numbers.
• Double-check all your measurements because window blinds are custom and cannot be returned.
• Measure the window opening and not for the size you want your window blinds to be; the factory makes all necessary deductions required for the correct sizing.
• Don't measure old window blinds as your measurements may end up being too narrow.
• Don't assume that all your window blind sizes are the same. Measure every window and take multiple measurements to ensure you get accurate numbers.

How to Measure Windows for Blinds

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What You'll Need

• Steel measuring tape (for the most accurate measurements)
• Step ladder
• Pen
• Paper

Step 1: Decide on a Mounting Style

Now that you have your tools and the helpful knowledge above, it is time to decide what type of mount you prefer. There are two options to choose from – you can mount your window blinds on the inside or on the outside of the window frame.

Note: Each mount type requires a different measuring technique. Once you've made your choice, you can move onto measuring the windows.

Inside Mount

Inside-mounted window blinds are installed on the interior of the window casing or frame. They provide a clean and streamlined look that emphasizes your window's size and molding. Inside-mounted blinds are often paired with outside-mounted curtains, though they also work well with windows that don't have a lot of surrounding wall space. Inside mounts do not offer as much light control as outside mounts do.

Outside Mount

Outside-mounted window blinds are installed in one of three places on the exterior of the window casing – on the window molding, the wall, or the ceiling above the window. These types of blinds are more forgiving with measurements than inside mounts, and they offer more light control thanks to the blinds extending beyond the window itself. Although outside-mounted window blinds are the most convenient choice – and, therefore, the most common – do be aware that they can conceal the window trim, which is not suitable if you wish to emphasize yours.

Step 2: Measure for Inside Mount Blinds

To accurately measure for inside-mounted window blinds you need to measure the following:

Measure the Width: For inside-mounted window blinds, measure the interior width of the window frame in three places: the top, the middle, and the bottom, measuring them all from left to right. You will want to use the narrowest width of the three measurements.

Measure the Height: To get the height, measure from top to bottom on the left, middle, and right side of the window. The longest length of the three is the one you want to use. To keep the blinds from resting on the window sill, subtract 1/4" from the height. If you don't have a sill, then measure to the point you want the window blinds to fall.

Measure the Depth: The depth of your window directly affects the types of blinds you can choose. For a flush installation, you need to make sure the recess meets the minimum depth requirement necessary. Otherwise, your blinds will project slightly from the window molding. It's best to refer to the minimum mounting requirements section of your window treatment, but as a good rule of thumb, allow 1" to 4" for horizontal blinds and 3" to 4" for vertical blinds.

Measure the Diagonal: Make sure to measure from both the upper left to bottom right corners and the upper right to bottom left corners. If your two measurements differ significantly, you may be better off with outside-mounted window blinds to get the most privacy and light control.

Step 3: … Or Measure for Outside Mount Blinds

Take these measurements to find the correct size for your outside-mounted blinds:

Measure the Width: For outside-mounted window blinds, you must measure the width of the space you want covered. Always record measurements down to nearest 1/8". Make sure to take three measurements (the top, middle, and bottom) and select the widest of them.

Measure the Height: Before you can measure the height of your outside mount, you need to ensure you have at least 2" of flat space on the molding or wall above the window to accommodate the mounting bracket and headrail. Once you have established the location of your headrail, you can measure down to where you want your window blinds to rest. Make sure to take three measurements (the top, middle, and bottom) and select the longest of the three.

Make Allowances: Be sure to make allowances for obstructions like molding, deadbolts, and doorknobs that might get in the way. If you encounter any obstructions, you can use extension brackets to resituate your blinds to where protrusions are no longer visible. For increased light control and privacy, consider adding an extra 3" to the width and length of your measurements.

Tip!

Now that you’ve measured your windows, it’s time to find the right blinds. Read our guide Types of Blinds and Shades to learn more about the different styles available.

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