How to Measure for Blinds to Get the Perfect Fit

Mariel Loveland
Written by Mariel Loveland
Updated January 19, 2023
Mother playing with daughters in front of window with blinds
Photo: Zia Soleil / Getty Images

Let the sunshine in (but not too much)

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Adding blinds to windows is an easy way to limit the amount of light entering your space and complete the look of a room, and, luckily, learning how to measure for blinds is a snap. However, installing blinds that are too short or narrow may leave unwanted gaps, and blinds that are too long won’t sit flush with the window frame. Use this guide to measure for blinds accurately and get the perfect fit.

Why Do I Have to Measure for Blinds? 

Since windows come in all shapes and sizes, window treatments aren’t a one-size-fits-all solution. You need to measure for blinds because you want to ensure they’re long enough to cover the entire window but not so big that it causes issues.

If the width and length are too small, your blinds won’t sufficiently block out light or offer privacy. On the other hand, if the width and length are too large, your blinds will overhang, potentially protrude on obstructions like handles and window frames, or drag on the floor.

How Much Does It Cost to Measure Blinds?

Most homeowners can measure blinds for free if they have a measuring tape and a level. If you want to hire a professional, measuring blinds is wrapped into the cost of blind installation. Most homeowners spend $210 to $1,300 on professional blind installation, with the average homeowner spending around $750.

How to Prep For Measuring Blinds

Before you move ahead with your blinds project, you’ll need to pick the type of blinds. There are two types: inside-mount blinds and outside-mount blinds. Here are some key differences.

Inside-Mount Blinds 

Inside-mounted blinds attach inside the window casing, so they sit flush with the trim or wall. This feature provides a clean look, and is often the preferred choice for windows with decorative molding around them, as they won’t be covered by the blinds. Inside mounting is recommended in most cases, as long as the frame is deep enough. This is why it’s important to always refer to the manufacturer’s dimensions to ensure your windows have enough space to support the required depth. 

When you refer to the dimensions, there will be a minimum depth required and fully recessed depth requirements. If your windows meet the minimum depth requirements, you can still install the blinds using an inside mount, but keep in mind that they may protrude a bit. If your windows meet the fully recessed depth requirements, they’ll sit far enough back to be level with the wall or trim.  

Outside-Mount Blinds

Outside-mounted blinds are installed above the window frame, directly on the wall or trim. They’re usually wider than the windows, providing full coverage. That’s why they’re a popular choice for those looking to completely darken the room, as inside-mounted blinds can let some light in through the small gap between the frame and the blind. 

Moreover, outside mounting is a good choice for window frames with a shallow depth or for covering windows with surrounding obstructions, such as window cranks or handles.

How to Measure for Blinds: Inside Mounts

Man measuring for blinds using tape measure
Photo: JodiJacobson / Getty Images

Follow these steps to achieve the perfect fit for your inside-mounted blinds.

1. Measure the Width

Using your measuring tape, start from the top left corner of the inside of the window frame, and measure across the distance to the inside edge of the right corner. This measurement is the width. Repeat this process in the middle and bottom sections to get three total measurements. Take the smallest measurement of the three to get the total width.

Depending on the manufacturer, you may have to round the measurements down, so always refer to the measuring instructions. If needed, take the shortest of the three width measurements, then round it down to the nearest ⅛ inch. When taking measurements, it’s important to accurately read the measuring tape to get precise results. 

2. Measure the Height

To find the height, bring the tape measure to the top left corner of the inside of the window frame, and measure downwards. Repeat this process in the middle of the window, and from the far right corner, inside of the frame, to take three vertical measurements. Use the longest measurement of the three for the height.

Check the manufacturer to determine whether you need to round up to the nearest ⅛ inch when transferring the measurements to order the blinds.

3. Measure the Depth

To determine the depth of your windows, take the tape measure, and extend the hook to the back of the window, as far as it will go. Read the measuring tape to the nearest ⅛ inch to find the depth.

If you have any obstructions, like window cranks or handles, measure from the point of the obstruction to the edge of the window frame. Refer to the product specifications to determine the minimum inside depth requirement and the fully recessed requirement to mount the blinds of your choice.

4. Transfer Measurements

Once you have the window’s width, height, and depth, you can bring these measurements to your local home improvement store, or transfer them to the factory’s website to order them based on your dimensions.

How to Measure for Window Blinds: Outside Mounts

Man measuring for blinds using tape measure
Photo: Jupiterimages / Getty Images

Follow these steps to achieve the perfect fit for your outside-mounted blinds.

1. Determine the Headrail Mount Position

Before measuring for the outside blinds, pick the location for the headrail mount. This spot usually falls somewhere between 1 to 3 inches above the window, but it can be higher or lower, depending on the style of the blinds and your personal preferences. 

2. Calculate the Width

If your window has trim, start from the outside edge of the left side trim to the outside edge of the right side trim. If your window doesn’t have trim, measure from the edge of the opening of the window from left to right.

Add at least 3 inches to the final measurement to prevent light from coming in through the sides of the blinds.

3. Calculate the Height

If your window has a window sill, begin your measurements from the bottom of it and take the tape measure 3 inches above the top of the window frame to allow for the headrail mounts and hardware.

If there isn’t a window sill, or if it doesn’t protrude, begin the measurements from the bottom of the window frame, and bring the tape measure up to the designated headrail mount position (typically 1 to 3 inches above the window).

Keep in mind that you may want the blinds to fall lower than the window to add privacy, prevent light gaps, and overall styling purposes. If so, add this amount (typically 2 to 3 inches) to the total height.

4. Transfer Measurements

Once you have the width and the height of the window totaled, you can bring these measurements to the store or factory to order the outside-mounted custom blinds.

How to Measure Windows for Blinds: Special Circumstances

Some parts of the window may make it more challenging to get accurate measurements. Follow these guidelines for navigating around unique window challenges.

Measuring Valances

A valance is the top piece of the window treatment, typically made from wood, fabric, or metal, that is decorative in nature to top off the blinds and hide hardware or curtain rods. They can either be mounted inside the window frame, or outside of the window frame, depending on your needs.

  • Inside-mounted: If you’re mounting the valance inside the window (remember, it must have enough depth to keep the valance mounted flush inside), measure the width between the window frame on the uppermost edge. Then, round up to the nearest ⅛  inch to get the width of the inside-mounted valance.

  • Outside-mounted: Outside-mounted valances are typically installed over an existing window treatment to cover hardware or the headrail. To determine the measurement of an outside-mounted valance, measure the width of the existing window treatment, then add 2–3 inches on each side to get the total width. 

Measuring Rollers and Shades

Rollers and shades are different types of window treatments similar to traditional blinds. Like slatted blinds, they’re either inside- or outside-mounted, but you’ll need to approach measuring with a slightly different technique.

  • Inside-mounting: To measure for rollers or shades, you only need to measure once across the top section to get the total width. (You may need to round down to the nearest ⅛ inch, depending on the manufacturer.) Then, measure from the top of the window opening to the windowsill (or the desired endpoint if there isn’t a windowsill).

  • Outside-mounting: To measure for rollers or shades mounted outside the window frame, measure from the outermost points of the headrail, then add 2 to 4 inches to get the total width. The extra material will hide any potential light that may otherwise leak through the gaps. When measuring the length, use the shortest of the three measurements, if you want the blinds to sit flush with the bottom of the window frame or sill. Otherwise, measure to the endpoint where you’d like the blinds to sit to determine the total length.

French Doors

If you’re installing blinds over French doors, measure 2 to 3 inches above the top glass pane and 1 inch past the side glass panels—this is where you’ll begin your measurements. 

Measure the width from the left to right, an inch away from the glass window panes. Then, measure the height from the top point to 2 to 3 inches past the bottom panel to get your final measurements.

Tips for Measuring Blinds for Accuracy

Check out these tips and tricks for ensuring your blind measurements are spot on.

  • Use a steel tape measure rather than cloth to get the most accurate measurements.

  • If you’re replacing blinds, be sure to take measurements of the window, not the blinds, for the most accurate results.

  • Always measure to the closest ⅛-inch for accuracy and don’t transpose measurements.

  • Write down the width first, then the height.

  • To make a window seem taller, consider mounting the shades above the window opening.

  • You can layer draperies on top of shades to make a design statement in the room, while drawing the eye upward to make the windows seem larger than they actually are.

  • Consider using outside mounting shades to make off-center windows feel more centered. Take the measurements of all the windows in the space, then add a few inches to the outside-mounted treatments to create more balance in the room.

DIY vs. Hire a Pro

For most homeowners, measuring for blinds won’t cost a dime. All you need is a measuring tape and a level. That said, it does require accuracy or you might get stuck with blinds that don’t fit in your space. Then, you need to install them, which isn’t always straightforward.

If you’re planning to hire a blind installation company near you, measurements are often wrapped into the total cost of the job. Most people spend around $5 to $15 per square foot on their blinds, and professional installation usually only increases costs by $15 to $50 per window. You may find the extra cost worth knowing that the job will be done right the first time.

Frequently Asked Questions

Measuring is the best way to know what size blinds you need. To get the right dimensions, take three key measurements: the width, height, and depth of the window.  Sometimes windows are not completely level or plumb, so measurements will differ from point to point. To avoid issues, measure the width and height in three places. Use the narrowest width measurement and the longest height measurement (providing there is no significant obstruction).

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