How to Measure Windows for Blinds: A Complete Step-by-Step Guide

How to Measure Windows for Blinds: A Complete Step-by-Step Guide

Choosing the perfect blinds starts long before installation. One of the most important steps is getting accurate window measurements. Even a small measuring mistake can affect how your blinds fit, operate, and look once installed.

Whether you're considering roller shades, zebra blinds, Roman shades, vertical blinds, or other custom window coverings, this guide will help you understand how to measure your windows correctly.

At Bellora Blinds, we also offer professional in-home consultation and measurement services throughout Toronto, Vaughan, and the Greater Toronto Area, so you don't have to worry about getting the measurements right on your own.

What You'll Need to Measure Your Windows

Before you begin, prepare a few simple tools:

A steel measuring tape A pencil or pen Paper or a phone for recording measurements A step stool or ladder for taller windows

For the most accurate results, we recommend using a steel measuring tape rather than a soft fabric measuring tape.

Measurements should also be recorded consistently. If you're ordering custom blinds, always confirm the measurement format required before placing your order.

Step 1: Decide Between Inside Mount and Outside Mount

Before measuring your window, you need to determine how you want your blinds installed.

There are two common installation methods:

Inside Mount

With an inside mount, the blind or shade is installed inside the window frame.

This creates a clean, streamlined appearance and allows the window trim to remain visible.

Inside mount blinds are a popular choice for modern interiors, but your window frame needs enough depth to accommodate the selected blind or shade.

Inside Mount Advantages Clean and built-in appearance Window trim remains visible Minimal projection from the wall Works beautifully with many modern window styles

However, inside mounting may not be suitable for every window. Shallow frames, handles, cranks, or other obstructions can sometimes interfere with installation.

Outside Mount

With an outside mount, the blind is installed on the wall or trim surrounding the window rather than inside the frame.

Outside mounting can be particularly useful when the window does not have enough mounting depth.

It can also provide additional window coverage.

Outside Mount Advantages Can cover the entire window opening Useful for shallow window frames Can help reduce light gaps around the window Creates the appearance of a larger window Offers more flexibility with installation

Your choice between inside and outside mounting will determine how your measurements should be taken.

How to Measure for Inside Mount Blinds

Accuracy is especially important with inside mount installations because the blind needs to fit within the available window opening.

Step 2: Measure the Width

Measure the inside width of the window opening in three different locations:

Across the top Across the middle Across the bottom

Do not assume that all three measurements will be identical.

Homes can settle over time, and window frames are not always perfectly square.

For many custom blind systems, the smallest width measurement is used when determining the appropriate finished size.

Do not automatically make your own deductions unless instructed by your blind supplier or installer.

Step 3: Measure the Height

Next, measure the inside height of the window opening.

Take measurements at:

The left side The centre The right side

Again, record all three measurements.

The measurement used can vary depending on the type of window covering being installed, so provide the exact measurements rather than estimating.

Step 4: Measure the Window Depth

Window depth is often overlooked, but it is extremely important for inside mount blinds.

Measure from the front edge of the window opening to the nearest obstruction.

Possible obstructions include:

Window handles Locks Cranks Screens Trim Other hardware

Different blinds require different mounting depths.

For example, a roller shade may have different installation requirements than zebra blinds or Roman shades.

If you're unsure whether your window has enough depth, a professional measurement can prevent installation problems later.

How to Measure for Outside Mount Blinds

Outside mount measurements work differently because the blind will extend beyond the window opening.

Step 5: Measure the Desired Width

First, measure the width of the area you want the blind to cover.

Instead of measuring only the glass, consider how much additional coverage you want around the window.

Adding coverage beyond the window opening can help minimize visible light gaps and create a more finished appearance.

Make sure there is enough flat mounting space for the brackets or headrail.

Step 6: Measure the Desired Height

Measure from the point where you want the top of the blind to be installed down to where you want the blind to end.

Depending on the window, this may be:

At the bottom of the window trim Slightly below the window At the windowsill Closer to the floor for larger windows or doors

The ideal position depends on the window style and the type of blinds being installed.

Measuring Large Windows and Patio Doors

Large windows and patio doors require additional planning.

For wide openings, measurements should be taken carefully at several points because even small variations can become noticeable across a large installation.

You should also consider:

Door handles Opening direction Sliding door movement Furniture placement Available mounting space Desired privacy Light control Blind weight and operating method

For very large windows, dividing the opening into multiple blinds may sometimes provide easier operation and greater flexibility.

Professional measurement is highly recommended for oversized windows and patio doors.

Measuring Bay Windows

Bay windows can be more complicated because several blinds may need to meet at different angles.

Simply measuring the width of each window may not be enough.

You also need to consider:

Window angles Blind projection Headrail depth Handle clearance Gaps between adjoining blinds

Incorrect calculations can cause blinds installed on neighbouring windows to interfere with each other.

For this reason, professional measurement is usually the safest option for bay windows.

Measuring for Zebra Blinds

Zebra blinds combine alternating sheer and solid fabric sections, making proper positioning especially important.

Before measuring, determine whether you prefer an inside or outside mount.

For inside mounts, check the available window depth carefully.

For outside mounts, consider extending the blind beyond the window opening to improve coverage and reduce light gaps.

Because the fabric rolls around the upper mechanism, also make sure there is sufficient clearance around window handles and other hardware.

Measuring for Roller Shades

Roller shades offer a clean and minimalist appearance, but it's important to understand that the width of the fabric and the overall width of the roller mechanism may not always be identical.

This means measurements should be taken according to the manufacturer's specifications.

For bedrooms or rooms where stronger light control is desired, an outside mount may sometimes provide better coverage around the edges of the window.

Measuring for Roman Shades

Roman shades add softness and texture to a room while maintaining a sophisticated appearance.

For inside mount Roman shades, carefully check:

Window width Window height Mounting depth Window handles and hardware

For outside mounts, determine how far you want the shade to extend beyond the window opening.

Proper measurements help the shade hang evenly and maintain its intended folds.

Common Window Measuring Mistakes

Even seemingly small mistakes can affect the final installation.

Some of the most common problems include:

Measuring only once

Always measure the window at several points.

Assuming the window is perfectly square

Many windows have slight variations between the top, middle, and bottom.

Using a fabric measuring tape

A rigid steel measuring tape generally provides more reliable measurements.

Rounding measurements too aggressively

Small differences can matter when ordering custom window coverings.

Making deductions yourself

Manufacturers and installers may already account for necessary installation clearances.

Ignoring handles and window hardware

A blind that technically fits the opening may still interfere with the operation of the window.

Measuring the glass instead of the window opening

Unless specifically instructed otherwise, blind measurements are generally based on the mounting area rather than simply the visible glass.

Should You Measure Your Windows Yourself?

For simple windows, taking preliminary measurements yourself can help you explore options and estimate what type of blinds may work.

However, when ordering custom-made blinds, professional measurements can provide additional peace of mind.

This is particularly valuable for:

Large windows Bay windows Patio doors Motorized blinds Multiple-window installations Unusual window shapes Windows with limited mounting depth

Professional measurement also allows the installer to inspect mounting surfaces, window hardware, and potential installation challenges before the blinds are produced.

Professional Blind Measurement in Toronto, Vaughan & the GTA

Beautiful custom blinds start with the right measurements.

At Bellora Blinds, we help homeowners choose window coverings that complement their space while providing the privacy, light control, and functionality they need.

Our in-home consultation process allows us to evaluate your windows, take accurate measurements, discuss mounting options, and help you select suitable styles and materials.

Whether you're considering zebra blinds, roller shades, Roman shades, vertical blinds, motorized blinds, or custom window coverings, we'll help you find the right solution for your home.

Let Bellora Blinds Measure for You

Not sure whether you should choose an inside or outside mount?

Have an unusually large window?

Planning blinds for your entire home?

You don't have to figure everything out yourself.

Book a free in-home consultation with Bellora Blinds.

We'll measure your windows, discuss your options, and help you choose window coverings designed for your space.

Bellora Blinds Beautiful Windows. Beautiful Homes.

Serving Vaughan, Toronto and the Greater Toronto Area.

Call: +1 647-916-0864