Figuring out how to measure a window well doesn't have to be a headache, even if you aren't exactly a pro with a tape measure. Whether you're looking to replace a rusted-out cover or you're installing a brand-new egress system for a basement bedroom, getting the right numbers is the difference between a perfect fit and a return shipment you'll have to haul back to the post office. Most people assume they can just eyeball it or take one quick measurement across the middle, but there's actually a little more strategy involved if you want things to line up right.
The goal here is to make sure your basement stays dry, your home stays safe, and you don't end up with a cover that wobbles or leaves giant gaps for critters to crawl through. Let's walk through the process step-by-step so you can get it done right the first time.
Grab Your Tools and Get Ready
Before you even step outside, make sure you have what you need. You don't need anything fancy, but a stiff metal tape measure is way better than a flexible fabric one. Fabric tapes can stretch or sag, and when we're talking about an inch or two making the difference between a cover fitting or falling into the well, accuracy matters.
You'll also want a notepad and a pen. I know it's tempting to just "remember" the numbers, but trust me, by the time you walk back inside, you'll be questioning if the width was 42 inches or 44 inches. If your window wells are a bit older and maybe a little overgrown, bring a broom or a small hand shovel to clear out any dirt or debris that might be hiding the edges of the well.
Measuring the Width of the Well
The first thing you need to find is the width. When you're learning how to measure a window well, the "width" usually refers to the distance along the house wall.
Stand inside the well if it's large enough, or just lean over the edge. You want to measure from the very outside edge of the well's rim on the left to the very outside edge on the right. If you have a corrugated metal well, don't just measure the inside opening; measure to the far edges of the "lips" or flanges where the metal attaches to the house.
Why the outside edge? Because most covers are designed to sit on top of the well wall, not inside it. If you measure the inside, your cover might be too small and could slip right through the middle. If the well is slightly warped (which happens a lot with older metal ones), take a couple of measurements—one right against the house and one a few inches out. Use the largest measurement to ensure the cover actually covers the whole thing.
Measuring the Projection
Next up is the projection. This is just a fancy word for "how far does it stick out from the house?" This is probably the most important measurement for getting a cover that doesn't leave a gap.
Place the end of your tape measure firmly against the foundation of your house. Pull it straight out to the furthest point of the window well's curve or front edge. Again, make sure you're measuring to the outer edge of the rim.
If your window well is rectangular, this is pretty straightforward. If it's circular or U-shaped, make sure you're finding the very "peak" of that curve. Sometimes the well isn't perfectly centered on the window, so check the projection on both the left and right sides just to be sure it's even. If one side sticks out 36 inches and the other is 37, go with the 37. It's always better to have a slightly larger cover than one that leaves your basement window exposed to the rain.
Don't Forget the Height and Depth
While the width and projection tell you the size of the "lid" you need, the depth and height are crucial for safety and drainage.
First, measure the depth of the well. Stick your tape measure down into the well until it hits the gravel or the drain at the bottom. Measure up to the very top lip of the well. If you're planning on installing a ladder (which is often required by law for basement bedrooms), you need to know exactly how deep that hole is.
Next, check the height of the window relative to the well. Does the window stick up above the top of the well? This is super common. If your window frame or the "casement" sits higher than the metal or plastic well itself, you can't just use a flat cover. You'll likely need a "stand-off" or a "sloped" cover that accounts for that extra height. Measure from the top of the well wall to the top of the window frame so you know how much clearance you need.
Dealing with Different Well Shapes
Not all window wells are created equal. If you have a standard semicircle or U-shaped well, the width and projection method works perfectly. But if you have a rectangular well, you'll want to measure the width at the house and the width at the very front. Sometimes those walls can bow out or cave in over time.
For concrete wells, things can be a bit tricky because they aren't always perfectly level. Use a level if you have one to see if the top of the concrete is flat. If it's slanted away from the house, you might need to adjust how you mount your cover.
If you have a plastic or composite well, these often have very specific rounded corners. It's helpful to take a photo of the well from directly above so you can compare it to the shapes offered by manufacturers.
Why Accuracy is Such a Big Deal
You might think, "Hey, it's just a hole in the ground, why does it have to be perfect?" Well, there are a few reasons. First is safety. If a window well cover doesn't fit correctly, a child or a pet could step on it and have it flip over like a manhole cover in a cartoon. A well-fitted cover should be secure.
Second is moisture control. The whole point of a cover is to keep rain, snow, and leaves out of that well. If your measurement is off by two inches, you might have a gap that funnels rainwater directly toward your basement window. That's a recipe for a flooded basement and a very expensive repair bill.
Lastly, there are building codes. If your basement has a bedroom, that window is an "egress" point—an emergency exit. There are very specific rules about how much clear space needs to be in that well so a firefighter with an air tank can fit inside, or so you can get out in a hurry. If you buy a cover that's too small or the wrong shape, you might actually be violating local fire codes.
A Few Pro Tips for the Road
Before you go ordering parts, here are a few things I've learned the hard way:
- Measure twice. It's a cliché for a reason. Do the whole process, go get a glass of water, and then do it again. If the numbers match, you're golden.
- Check for obstructions. Is there a water spigot inside the well? Is there a gas line running nearby? Does the siding of your house overhang the well? These things can change how a cover sits.
- Account for the "lip." If your window well is made of plastic and has a thick 2-inch lip all the way around, make sure your width measurement includes that.
- Think about the "height above grade." If the top of your window well is level with the ground, you'll need a different style of cover than if it sticks up six inches.
Knowing how to measure a window well is really just about taking your time and being thorough. Once you have those three or four key numbers—width, projection, and depth—you're ready to shop with confidence. You'll save yourself the hassle of returns and, more importantly, you'll keep your basement dry and your family safe. It's one of those quick DIY tasks that feels great once it's done, mainly because you won't have to think about it again for another ten years.