How to Measure Windows for Blinds & Shades

Tools You Will Need

Before you begin measuring, gather the following tools. Having everything ready will make the process faster and more accurate.

• Steel measuring tape (not cloth) — a 25-foot tape with 1/8-inch markings is ideal
• Pencil — for marking measurements directly on the window frame
• Notepad or phone — to record each measurement as you go
• Step ladder — to safely reach the top of taller windows

Inside Mount Measurements

An inside mount installs the blinds within the window frame opening, creating a clean, built-in appearance. Follow these steps for precise inside mount measurements.

Width

1. Measure the width of the window opening at three points: the top, the middle, and the bottom of the frame opening.
2. Record the smallest width measurement. This ensures the blinds will fit inside the opening without binding.

Height

1. Measure the height of the window opening at three points: the left side, the center, and the right side.
2. Record the longest height measurement. This ensures full coverage of the window opening.

Depth

1. Measure the depth from the front edge of the frame opening to the glass at three points along the frame.
2. Use the smallest depth measurement to determine whether your chosen product will fit as a flush inside mount.
3. Check the minimum depth requirement for your product type:
   • Standard blinds: typically 1.5 to 2 inches
   • Cellular / honeycomb shades: 0.75 to 1.5 inches
   • Roller shades: 1.5 to 2.5 inches

Always measure to the nearest 1/8 inch. Precision is critical for a proper inside mount fit.

Outside Mount Measurements

An outside mount installs the blinds above and outside the window frame, covering the entire opening and overlapping the surrounding wall or trim. This is ideal for shallow window frames or when you want maximum light blocking.

Width

1. Measure the width at three points: the top, middle, and bottom of the area you want to cover.
2. Use the largest measurement to ensure full coverage.
3. Add 2 to 3 inches on each side (4 to 6 inches total) for light gap coverage. This overlap prevents light from leaking around the edges.

Height

1. Measure the height from your desired top mounting point to your desired bottom point (typically the window sill or below).
2. Ensure there is a minimum of 2 inches of vertical space above the window for mounting brackets. This space is needed regardless of wall or trim mounting.

Inside vs Outside Mount Comparison

Choosing between inside and outside mount depends on your window frame depth, desired look, and light control needs. Use the table below to compare.

Specialty Windows

Not all windows are standard rectangles. Here is how to approach measuring for the most common specialty window types.

Arched Windows

Arched windows require custom blinds that match the exact curvature of the window. Standard rectangular blinds will not fit. Because of the complexity involved, professional measurement is strongly recommended. A certified installer will create a precise template of the arch to ensure a perfect fit.

Bay Windows

Bay windows consist of multiple sections or panes set at angles. Measure each section or pane separately — do not measure the entire bay as one unit. For complex angles, create cardboard templates of each pane to verify your measurements. Install individual blinds on each pane for the best fit and operation.

Skylights

Skylights are mounted overhead and are difficult to reach, so motorized or remote-controlled blinds are strongly recommended. Measure the exact opening of the skylight frame. Consider solar-powered motors, which eliminate the need for electrical wiring to the ceiling and are easy to install on retrofit projects.

French Doors

For French doors, measure the glass area only — not the full door dimensions. You will need shallow-profile blinds or shades that do not interfere with the door operation. Be sure to account for handle clearance: measure the distance from the glass to the door handle and choose a product with a headrail and bottom rail that fit within that space.

Common Measuring Mistakes

Avoid these seven common mistakes that lead to poorly fitting blinds and costly returns.

1. Using a cloth tape measure — Cloth tapes stretch over time and produce inaccurate readings. Always use a steel tape measure.
2. Measuring only once — Always take measurements at three points (top, middle, bottom for width; left, center, right for height). Windows are rarely perfectly square.
3. Rounding measurements — Record every measurement to the nearest 1/8 inch. Rounding to the nearest half or whole inch is the single most common cause of fit problems.
4. Not checking frame depth for inside mount — Each product type requires a minimum depth for flush mounting. If your frame is too shallow, switch to an outside mount.
5. Measuring frame-to-frame instead of opening width — For inside mount, measure the clear opening between the frame surfaces, not the outer frame edges.
6. Not accounting for obstructions — Check for handles, cranks, trim pieces, and other hardware that may interfere with the blinds. Note these on your measurement worksheet.
7. Assuming all windows are the same size — Even windows that look identical can differ by 1/4 inch or more. Measure every window individually.

Measurement Worksheet

Use this worksheet to record your measurements for each window. Keeping organized records prevents ordering errors and makes reordering easy in the future.

For each window in your home, record the following:

• Window name / location — e.g., "Master Bedroom Left," "Kitchen Above Sink"
• Width — three measurements: top, middle, and bottom
• Height — three measurements: left, center, and right
• Depth — from frame edge to glass (for inside mount)
• Mount type chosen — inside or outside
• Any obstructions noted — handles, cranks, trim, sensors, or other hardware

Label each window clearly and double-check your numbers before placing an order. A few extra minutes of verification can save weeks of waiting for replacement blinds.