Expert Guide: Site Measurement for Custom Blinds (What Professionals Don’t Tell You) 

Measuring for custom blinds might feel daunting, but most homeowners get it right on their first try. With accurate measurements, you’ll avoid gaps, cut energy costs, and ensure a polished look. This guide breaks down the process step by step, so your blinds fit perfectly every time. 

Decide on Mount Type First 

Before grabbing your measuring tape, you must first determine how your blinds will be installed. The mount type is the foundation of your entire project and directly impacts both the measuring process and final appearance of your custom blinds. 

Inside mount vs outside mount: what’s the difference? 

Inside mount blinds fit neatly within the window frame, creating a clean, built-in appearance that showcases your window trim. The brackets attach to the “ceiling” or sides of the window opening, allowing the blinds to sit flush with the wall or trim when properly installed. 

Outside mount blinds, conversely, are installed either on the wall above the window or directly on the window trim. These blinds extend beyond the window opening, typically overlapping the window frame by several inches on all sides for complete coverage. 

How mount type affects your measurements 

The mount type changes how you measure for custom blinds. For inside mounts, measure the exact window opening size from edge to edge. At Newlines, we make the necessary adjustments during production to ensure a precise, smooth fit. 

For outside mounts, the process is different. Measure the size you want your blinds to cover, usually adding 2 to 3 inches on each side of the window opening for better light control and privacy. Accuracy is especially important with inside mounts, since even the smallest variation in width, height, or depth can affect the fit. 

When to choose inside or outside mount 

Most homeowners choose an inside mount because it provides a sleek, built-in look that highlights the window frame. At Newlines, we usually recommend this option whenever the window has enough depth, as it ensures a neat fit and modern finish. 

 Inside mount works best when: 

• Your window frame has sufficient depth (typically at least 2-2.5 inches) 

• You want to showcase decorative trim 

• Your window has a clean, even surface 

Outside mount is the better option when: 

• Window frames are too shallow for hardware installation 

• Obstructions like cranks, handles, or alarm sensors exist 

• You need maximum light blockage and privacy 

• Your window opening isn’t perfectly square (more than ½ inch difference in diagonal measurements) 

• You want to make small windows appear larger 

First-time buyers often worry about making the wrong choice. Rest assured, there’s no universally “better” option, the right mount type depends entirely on your specific windows and preferences. 

Essential Tools for Accurate Custom Blind Measurement 

Gathering the right tools is the initial step towards successful site measurement for custom blinds. Without proper equipment, even the most careful person might make errors that lead to ill-fitting window treatments. 

Steel tape measure vs cloth tape 

The single most important tool for custom blind measurement is a steel tape measure. Unlike cloth or fabric alternatives, steel tapes provide significantly greater accuracy. This isn’t a minor difference, cloth tapes stretch over time, potentially leading to measurement errors that can make your custom size blinds unusable. 

Steel tape measures hold their shape without sagging or bending while measuring awkward angles or recesses. This rigidity ensures much greater precision, particularly important since you’re often dealing with millimetres rather than centimetres. When mounting blinds inside window frames, place the base of the tape measure on one side, then extend the metal tip to the other remembering to add the size of the tape base to your overall measurement. 

Why a level and ladder might help 

For taller windows or high-mounted frames, a step ladder becomes essential. Rather than balancing precariously on furniture (which is neither safe nor precise), a sturdy ladder provides stable access to all parts of your window. 

A spirit level or digital level serves as another valuable ally. This tool helps verify whether your window frame is perfectly horizontal or vertical, especially important for inside mounts where slight variations can dramatically impact the final fit. By checking for plumb lines, you’ll know if adjustments are needed to ensure your blinds hang straight. 

Recording tools: pen, paper, or phone 

Never trust your memory when taking measurements. While some people prefer recording dimensions on their phones, a physical notepad offers distinct advantages. It allows you to quickly sketch window layouts and reduces the risk of accidentally deleting crucial information. You can also cross-check measurements at a glance. 

Whichever recording method you choose, maintain a systematic approach. Label each window clearly alongside its corresponding dimensions to prevent costly mistakes when ordering. For added confidence, many professionals recommend measuring twice, a few extra minutes spent double-checking can save hours of frustration later. 

Step-by-Step Guide to Measuring Your Windows 

Getting accurate measurements stands as the foundation of properly fitting custom blinds. With steel tape measure in hand, let’s tackle this process methodically. 

Step 1: Choose Mount Type 

Decide whether you want an inside mount or an outside mount. Inside mounts fit neatly within the window frame for a sleek look, while outside mounts cover beyond the frame for maximum light control and privacy. At Newlines, we guide you on the best option based on your window type and design preference. 

Step 2: Measuring for Inside Mount Blinds 

• Width: Measure across the top, middle, and bottom of the frame. Record the smallest measurement. Do not make deductions—Newlines will adjust for clearance. 

• Height: Measure from the top inside edge to the sill on the left, centre, and right. Use the longest measurement. 

• Depth: Check the depth of the window frame to confirm the blinds can fit, and look for obstructions such as handles or locks. 

Step 3: Measuring for Outside Mount Blinds 

• Width: Measure the exact width you want the blinds to cover, then add 2–3 inches on each side (4–6 inches total) for better coverage. For vertical blinds, add 3 inches on each side. 

• Height: Start measuring from the point where you plan to mount (often 3 inches above the frame) down to the sill or desired length. 

Step 4: Write Down Your Measurements 

Always write down width first, followed by height (e.g., 36″ W x 72″ H). Double-check your notes to avoid mistakes. 

Step 5: Choose the Side for Controls 

Decide whether you want the cord or wand on the left or right side. Choose based on convenience and accessibility in your room layout. 

Once you’ve got your measurements, share them with us at Newlines and our team will help you craft the perfect custom blinds for your home. 

What Professionals Don’t Tell You (But You Should Know) 

Many DIY enthusiasts encounter unexpected challenges when measuring for custom blinds that professional installers rarely mention. These insider secrets can make the difference between perfect-fitting treatments and costly disappointments. 

Why measuring each window separately matters 

Even windows that appear identical often vary by several millimetres due to settling, construction tolerances, and frame warping over time. Surprisingly, windows installed during the same construction project can differ by up to ¼ inch in width or height. Measuring each window individually prevents frustrating mismatches. 

How small errors can lead to big problems 

In reality, a measuring error as small as ⅛ inch can cause significant issues. Blinds that are even slightly too wide won’t fit into inside mounts, whilst too-narrow blinds create unsightly light gaps. Height measurement errors might mean blinds hitting windowsills or leaving large gaps at the bottom. 

Understanding manufacturer deductions 

Most manufacturers automatically subtract a small amount (typically ⅜ inch from width and ¼ inch from height) from inside mount measurements to ensure proper operation. Double-checking a company’s specific deduction policy prevents surprises when your blinds arrive seemingly “too small.” 

Tips for avoiding light gaps and poor fit 

For optimal results, measure to the nearest ⅛ inch rather than rounding up or down to whole numbers. Additionally, when ordering multiple blinds for adjacent windows, consider consistent outside mount dimensions for visual harmony. Finally, always note which measurement is width versus height, a commonly overlooked detail that causes most ordering errors. 

Conclusion 

Accurate measurement is the key to blinds that look great and work perfectly. With the right steps, you can avoid costly mistakes and achieve a professional fit on your own. Thousands of homeowners do it successfully, and you can too. 

At Newlines, we offer a full range of indoor blinds Roller, Vertical, Venetian, Zebra, Roman, Honeycomb, Panel, Ripple, and Sheer Shades as well as outdoor systems like Outdoor Roller Blinds and Zip Blinds. Whether you’re refreshing a single room or upgrading your entire home, our team is here to guide you from measurement to installation. 

Double-check your measurements, choose your preferred style, and let Newlines craft blinds that fit your windows flawlessly. Contact us today for personalised advice or to get started with your order. 

Frequently Asked Questions