How To Measure Windows For Blinds

If you are standing in front of your window, holding a tape measure and feeling a knot of anxiety in your stomach, take a deep breath. You are not alone.

Our recent customer survey revealed a staggering statistic: Over 50% of homeowners cite “fear of incorrect measurements” as their #1 hesitation when buying blinds online. It makes sense—custom blinds are an investment, and nobody wants to be stuck with a shade that is half an inch too wide to fit the bracket.

But here is the secret: You don’t need to be a professional contractor to get professional results. You just need a steel tape measure and the “3-Point Method.” This guide will walk you through the process, step-by-step, ensuring a perfect fit for your home.

Step 0: The Golden Rules

Before you measure a single inch, follow these three non-negotiable rules to avoid disaster.

1. Steel Tape Only: Never use a cloth tape measure (like for sewing) or a ruler. Cloth stretches, and rulers slip. Use a sturdy steel tape measure for accuracy.
2. Measure Every Window: Even if your three living room windows look identical, they probably aren’t. Houses settle, and frames shift. Measure each one individually.
3. Round to the Nearest 1/8″: Precision matters. Don’t round to the half-inch. Read the little lines on the tape measure.

Step 1: The Big Decision – Inside vs. Outside Mount

The way you measure depends entirely on where you want the blind to sit.

Option A: Inside Mount (The Modern Look)

The blind sits inside the window casing.

• Why choose it: It provides a clean, built-in look and showcases your window molding.
• The Catch: Your window frame must be deep enough (usually at least 2-3 inches), and your measurements must be precise.

Option B: Outside Mount (The Problem Solver)

The blind mounts on the wall above the window or on the trim itself.

• Why choose it: It makes windows look larger, hides ugly molding, and blocks more light (great for bedrooms).
• The Catch: It covers the architectural details of the window frame.

Step 2: How to Measure for INSIDE Mount

This is the most common choice, but it requires the “3-Point Method” to account for windows that aren’t perfectly square.

1. Measure the Width (The Most Critical Step)

Measure the inside of the window frame in three places:

1. Top: Measure inside the frame at the very top.
2. Middle: Measure inside the frame in the center.
3. Bottom: Measure inside the frame at the bottom.

✅ The Rule: Circle the narrowest measurement. Why? If you use the widest number, the blind will get stuck in the narrow part of the frame. The factory will take a tiny deduction (usually 1/4 inch) from the number you provide to ensure smooth operation—so do not make your own deductions. Give them the exact size of the opening.

2. Measure the Height

Measure from the top inside jamb to the window sill in three places:

1. Left side
2. Center
3. Right side

✅ The Rule: Circle the longest measurement. Why? This ensures the blind is long enough to cover the entire window when fully closed.

Step 3: How to Measure for OUTSIDE Mount

Since there is no frame to restrict you, you have more freedom here.

1. Measure the Width: Measure the area you want to cover. We recommend adding 2 to 4 inches to each side of the window frame (total 4-8 inches extra). This overlaps the wall and prevents light gaps.
2. Measure the Height: Measure from where you plan to mount the headrail (usually 2-3 inches above the frame) down to the bottom sill (or lower if you want to cover the sill).

Step 4: The Hidden “Gotchas” (Don’t Skip This!)

Our survey showed that many frustrations come from “obstructions.” Before you order, check for these:

• Window Depth: For inside mounts, verify you have enough depth for the mounting bracket. Most blinds need at least 2 inches of flat space.
• The “Cranks” and Handles: Do you have casement windows with crank handles that stick out? If so, an inside mount blind might hit the handle when you try to lower it. You may need to switch to an outside mount or look for “slim profile” blinds.
• Tile or Trim: Check if there is tile or decorative trim at the bottom of the window that might interfere with the blind closing fully.

Measuring takes about 5 minutes, but the peace of mind lasts for years. By following the 3-Point Method, you eliminate the guesswork.

Still worried about getting it wrong? We understand. That is why we are developing solutions like LazBlinds—designed with higher tolerance and easier installation methods, so you don’t have to stress over every 1/8th of an inch.

But for now, grab that steel tape measure, follow the steps above, and get ready to transform your home!