The Complete Guide to Measuring Windows for Motorized Blinds

When ordering custom motorized blinds, your measurements determine everything. Unlike off-the-shelf window treatments, custom shades are fabricated to your exact specifications — measured to 1/8 of an inch. A measurement error of even 1/4" can mean a shade that won't fit, gaps that leak light, or a return that costs you time and money. The good news: measuring is straightforward if you follow a systematic approach.

Tools You'll Need

• Steel tape measure (25 ft) — never use a cloth or plastic tape, which can stretch up to 1/2" over 36 inches
• Pencil for marking reference points on the window frame
• Paper or phone to record measurements immediately (label each window by room and position)
• Step stool for windows above 5 feet

Inside Mount vs. Outside Mount: Which Should You Choose?

Definition — Inside Mount: The shade is installed inside the window frame, sitting flush with the wall for a clean, built-in look. Requires a minimum frame depth of 1.5 inches (2.5" recommended for motorized shades with a larger headrail). Definition — Outside Mount: The shade mounts on the wall or trim above the window opening. Ideal when frame depth is under 1.5", when you want to block maximum light, or when you want windows to appear larger. Factor Inside Mount Outside Mount AppearanceSleek, built-inBold, makes window look larger Min. Frame Depth1.5" (2.5" for motorized)No requirement Light BlockageSmall light gaps at edgesSuperior — overlaps frame Best ForStandard windows, modern lookShallow frames, bedrooms, home theater

Step-by-Step Measuring Instructions

Step 1: Measure the Width

Take three width measurements across the window opening:

1. Top: Measure the width at the top of the window frame, from inside edge to inside edge.
2. Middle: Measure at the center of the window.
3. Bottom: Measure at the bottom of the frame.

For inside mount: Use the narrowest of the three measurements. Record to the nearest 1/8".
For outside mount: Use the widest measurement, then add 2–4 inches on each side (4–8" total) for full light coverage.

Step 2: Measure the Height

Take three height measurements:

1. Left side: Measure from the top of the frame to the sill.
2. Center: Measure at the middle.
3. Right side: Measure at the right edge.

For inside mount: Use the longest measurement to prevent gaps at the bottom.
For outside mount: Add 3–4 inches above the frame and 2–3 inches below the sill for optimal coverage.

Step 3: Double-Check Everything

Repeat all measurements a second time. If your two sets don't match, measure a third time and use the median. Professional installers follow this exact protocol — it takes 2 extra minutes and prevents costly errors.

Measuring Special Windows

• Arch windows: Measure the width at the widest point and the height from the base of the arch to the peak. Provide a photo — most motorized arch shades require a template.
• Bay windows: Measure each panel separately. Note the angle between panels (typically 120° or 135°). Consider individual shades for each section rather than one continuous treatment.
• Skylights: Measure width and length of the glass area. Add 1" to each dimension. Motorized skylights require a side-channel track system — note the depth of the frame recess.

Common Measuring Mistakes to Avoid

1. Using a cloth tape measure — fabric tapes stretch and flex. A steel tape is accurate to 1/32".
2. Rounding measurements — never round to the nearest inch. Custom shades need 1/8" precision. 36-3/8" is not the same as 36".
3. Measuring only once — windows are rarely perfectly square. Three measurements at different points catches variations that a single measurement misses.
4. Forgetting to check frame depth — a shade that physically won't fit inside a shallow frame is the #1 return reason for inside-mount orders.
5. Confusing inside vs. outside mount dimensions — if you provide inside-mount measurements but select outside mount, your shade will be too small.

Frequently Asked Questions

What if my measurements are wrong?

Most custom shade manufacturers, including WindowShades360, have a tolerance of ±1/8". If your shade arrives and doesn't fit due to a measurement error greater than 1/4", you may need to reorder. Some companies offer a measurement guarantee program — if you follow their measuring guide and the shade doesn't fit, they'll remake it free of charge. Always save your measurement records.

How do I measure for no-drill shades?

No-drill motorized shades use tension brackets or adhesive mounts that attach to the inside of the window frame. Measure the inside width at three points (just like an inside mount) and use the narrowest measurement. Also measure the frame depth — most no-drill brackets need at least 1.25" of depth. For adhesive-mount options, ensure the surface is flat, clean, and non-porous.

Can I measure myself or do I need a professional?

For standard rectangular windows, DIY measuring is perfectly reliable if you follow the three-point method described above. Over 85% of our customers measure successfully on their own. Consider professional measurement for specialty shapes (arches, angles, skylights), whole-home orders of 10+ windows, or if your home has older construction with significantly out-of-square frames.