Measuring for Outside Mount Window Treatments

Measuring for Outside Mounts require less precision than for Inside Mounts, although it’s still best to use a metal tape measure or yardstick to ensure accurate measurements.

Window blinds using an Outside Mount

Modern Bathroom by Salt Lake City Architects & Designers Alice Lane Home Collection

Since Outside Mounts are more “forgiving”, they are the preferred choice for inexperienced DIY-ers. But they also provide more complete light blockage and privacy.

Although each manufacturer may have specific instructions regarding how the dimensions are to be calculated, the following provides a general overview of what’s needed.

Step-by-Step Instructions

Measure width at window center

up to the nearest 1/8 inch. This will be your WIDTH measurement.

Be sure to follow the manufacturer’s instructions carefully: some manufacturers want the specified width to include the overlap, while others will add a pre-specified amount to the opening width that you provide.

Measure height at center of window up to the nearest 1/8 inch. This will be your HEIGHT measurement.

Traditional Bedroom by Denver Interior Designers & Decorators Karen White Interior Design

Measure for Inside Mount Window Treatments

Traditional Roman Blinds by San Francisco Window Treatments Stitch Custom Furnishings

Inside mounted window blinds require more precise measurements, so always use a metal tape measure or yardstick to ensure the accuracy of your measurements.

First measure the window opening on the diagonals. If the two diagonal dimensions are not identical, the window is out of plumb (e.g. it’s skewed).

This is frequently the case, so you instead may want to use an Outside Mount if maximum window coverage for privacy and light blockage is an important consideration.

Measuring to ensure that window is plumb

picture from diy network

Result of using an Inside Mount on an out-of-plum window

Step-by-Step Instructions

First measure width in three places

down to the nearest 1/8 inch. This will be your WIDTH measurement.

Measure height in three places

down to the nearest 1/8 inch. This will be your HEIGHT measurement.

Repeat the process for each window, even if they are supposed to be the same size – they probably aren’t.

Traditional Roman Blinds by San Francisco Window Treatments Stitch Custom Furnishings

Be sure to follow the manufacturer’s instructions carefully: some manufacturers want the specified width to include the overlap and the height of the headrail, while others will add a pre-specified amount to the opening length that you provide.