Replacing a window sounds simple. But if your measurements are even slightly off, your new window won’t fit. That means extra costs, delays, and frustration. So before you order anything, you need to know exactly how to measure windows the right way. Moreover, you can also consult Trade UPVC to help you in this process.
So, this is the perfect guide for you to understand every detail about the measurements.
What Do You Need Before You Start Measuring?
Many people think that they need only a tape measure for taking measurements. This is not right, you have to gather the right tools.
Here are the tools that you need:
- A steel tape measure (never use a fabric one because it stretches)
- A pencil and a notepad to write down measurements
- A spirit level to check if the opening is straight
- A step ladder for windows that are high up
- A helper for large windows (two people = more accurate readings)
Should You Measure from the Inside or Outside?
Measure from the outside whenever possible. This gives you the most accurate reading of the full opening. When you measure from outside, you can see the complete structural gap where the window sits.
However, if outside access is difficult, measuring from the inside also works. Just make sure you are measuring the frame opening, not the window itself.
And here is the most important rule: never measure the old window frame. Old frames can warp, shift, or shrink over time. Always measure the actual opening in the wall from brick to brick or stud to stud.
Does Window Measurement Differ for Full-Frame and Pocket Replacement?
Yes, it does, and it is important to understand it too. There are two types of window replacement:
- Full-frame replacement: The entire window, including the old frame, is removed. Here, you measure the rough opening (brick to brick or stud to stud).
- Pocket/insert replacement: This is when the installer removes and replaces just the glass and the sash. The frame remains intact. For this, you measure the inside of the frame as it is.
Knowing what type of window replacement you have will help ensure your window measurements are accurate.
How Do You Measure a Window Step by Step?
Follow these instructions closely, and you will measure windows correctly.
Step 1: Measure the Width
Take your tape measure and place it horizontally across the opening. Measure at least three times:
- One at the top
- One in the middle
- One at the bottom
Openings are rarely perfectly straight, which is why three horizontal measurements are necessary. The three readings show you the narrowest point. Always use the smallest measurement of the three. This ensures your new window will fit even in the tightest spot.
Step 2: Measure the Height
Repeat the process above, now in a vertical position, with the tape measure. Measure at least three times:
- One on the left side
- One in the center
- One on the right side
Again, use the smallest reading. This is the standard rule for how to measure windows for replacement windows: always go with the smallest number.
Step 3: Check If the Opening Is Square
This step is often skipped, but do not skip it. Measure diagonally from the bottom-left corner to the top-right corner. Then measure from the bottom-right corner to the top-left corner.
If the measurements are equal, the opening is square.
If one measurement is larger than the other, the opening is considered racked, a phenomenon common in older houses. Let your window fitter know if your opening is racked before the order is placed. A professional can help advise on how to properly address this issue.
Step 4: Subtract the Fitting Allowance
Once you have your smallest width and height measurements, subtract a small amount for fitting. This is typically 1/4 inch to 3/8 inch from both width and height. In metric, this is around 10mm.
This small gap is necessary. It gives the installer room to level the window, add sealant, and make small adjustments. Because if the gap is too little, the window won’t fit, and if the gap is too much, you’ll get drafts and energy loss.
How to Measure for New Windows Based on Window Type?
The fundamental measurement process is the same, but a few styles require special attention. Here is a quick description of measuring for different types of replacement windows.
Double-Hung Windows
These are the most common in homes. Measure the rough opening width and height using the three-point method. Subtract the fitting allowance, and you are good to go.
Casement Windows
Casement windows are side-hinged windows. The width and height are measured using the same three measurement methods. It is vital that when placing an order, you record the direction that the window opens to, whether to the left or the right.
Sliding Windows
For sliding windows, use the same three-point method. Also, check that the opening is level, as sliding windows need a flat track to operate smoothly.
Bay Windows
Bay windows are more complicated as there are many sections that are joined together at different angles. These need to be measured separately, panels need to be recorded separately, and each panel needs to be measured once using the three measurement methods. Because of the high level of difficulty for these windows, it is worthwhile to have a professional from Trade UPVC to verify your measurements.
What Is the Standard Window Height and Why Does It Matter?
Knowing the height of a standard window helps you cross-check your measurements. The most common window heights are:
- 24 inches (small bathroom or basement windows)
- 36 inches (common in bedrooms)
- 48 inches (popular in living rooms)
- 60 inches (larger living spaces)
Standard window widths fall somewhere between 24 and 48 inches. If the measurements fall very far outside the typical range, a mistake was likely, and it is worth measuring again. The majority of houses (especially older ones) have window openings that are not standard, and therefore non-standard sizes are common.
What Are the Most Common Mistakes When Measuring Windows?
Here are the most common errors people make when learning how to measure for new windows:
- Measuring the old frame instead of the wall opening
- Only measuring once instead of taking three readings
- Forgetting the fitting deduction causes the windows to not fit
- When measuring at an angle, always keep the tape measure straight and level
- Mixing up width and height, most suppliers ask for width first, then height
A simple way to avoid all of these is to measure twice, record clearly, and always double-check before submitting your order.
FAQs
How do you measure a window for replacement?
You measure the width in three spots: the top, the middle, and the bottom. You then measure the height in three new locations: the left, the center, and the right. You take the smallest measurement in each of the instances. Then subtract 1/4 to 3/8 inch for fitting allowance.
How do you measure for replacement windows if the opening is not square?
Take your diagonal measurements. If they do not match, the opening is out of square. Use the smallest width and height readings and inform your installer so they can plan accordingly.
Should I let a professional measure my windows?
For a basic replacement, you can save money by measuring yourself, but for the final order, especially complicated designs like bay windows or full frame replacements, always have a professional double-check your measurements. If they are the ones doing the measuring, they will take responsibility for any mistakes.
Conclusion
The most critical step in window replacement is measuring correctly. Fortunately, the process of measuring for replacement windows is not difficult; you simply need to know and follow the right steps.
It is advised to measure three times, take the smallest reading, check for squareness, and subtract your fitting allowance. It is also important to know whether you are doing a full-frame or a pocket replacement. And of course, when in doubt, you should consult a professional, and Trade UPVC is a recommended one.
Take your time with the measurements now, and your new windows will fit perfectly the first time.
