Measure the well’s outside edges at its widest point — never the window — because covers fit the well opening, not the glass.
The tape has to run along the well itself: outer edge to outer edge for width and length, foundation wall to front lip for projection, and grade to top rim for height on metal wells.
What Do You Measure On A Window Well Cover?
You measure the well opening plus its attachment points, not the window frame. The cover has to clear the full opening and land on whatever material surrounds it.
Work through these for any well:
- Width and length: outside edge to outside edge, at the widest point of the well.
- Projection: from the foundation wall out to the front or outer edge of the well.
- Height above grade: required for metal wells, since the cover often mounts to the rim rather than sitting flat.
- Overhang: mark about 4 to 6 inches of cover resting on the wall, so the panel has something solid to bear on.
For concrete, plastic, wood, and brick wells, measure the outside dimensions first, then check inside dimensions as a fit confirmation. Curved or warped wells get measured at the widest point, and the largest reading wins — a cover sized to the narrow side will not seat.
Where Most Measurements Go Wrong
The most common error is measuring the window opening instead of the well, which produces a cover that is too small in every direction. Three others show up just as often: ignoring attachment flanges and lips on metal wells, skipping projection entirely, and never checking height above grade or how square the well actually is.
Metal wells deserve extra attention. Their flanges and lips add real width, and a cover cut to the bare well body will not sit flush over them. Measure out to the flange edge, not the well wall.
One more check before you order: if the window sits above the well, measure from the top of the well to the top of the window frame on both the left and right sides. Uneven readings mean the well is not level, and that gap decides whether a flat panel can rest without rocking.
| Well Type | Measure This Way | Extra Check |
|---|---|---|
| Metal | Outside edge to outside edge, plus projection | Height above grade and flange lips |
| Concrete | Outside dimensions, then inside dimensions | Cover overhang of 4 to 6 inches |
| Plastic | Outside dimensions at the widest point | Warping or out-of-square corners |
| Wood | Outside edge to outside edge | Rot or sag along the rim |
| Brick | Outside dimensions plus projection | Protruding mortar and uneven courses |
| Curved or irregular | Widest point only, largest reading wins | Re-measure at two or three spots |
| Egress wells | Outside dimensions plus horizontal area | At least 9 square feet of clear area |
How Do You Size A Cover When You Land Between Sizes?
You round up to the next stock size, because a slightly large cover can be trimmed or shimmed while a small one cannot be stretched. Measure the well at its widest point, include the flanges, and buy the next size up whenever the numbers fall between two stock panels.
Manufacturers list covers by length and projection. So a well measuring 46 inches long with a 20-inch projection lands on a 48″L x 22″P panel. Materials in current catalogs include polycarbonate, steel, and aluminum, so confirm the size exists in the material you want before ordering.
Egress wells carry their own numbers. A cover that blocks or crowds that opening defeats the point of the well.
Once your numbers are down, the next decision is which panel to buy. Our tested roundup of the best basement window covers compares fit, materials, and egress compliance so you can match a cover to the dimensions you just took.
Frequently Asked Questions
Can I Measure A Window Well From Photos?
No. Photos distort depth and cannot show flange widths, projections, or how far a well sits out of square. Use a tape measure on the actual well, take each reading twice, and write the numbers down before you go inside. If something must be estimated, note it on the order and expect to confirm on delivery.
Should The Cover Overlap The Window Well Wall?
Yes. Plan on roughly 4 to 6 inches of cover resting on the wall, then mark that overhang before ordering or cutting. The overlap is what keeps rain, leaves, and snowmelt from running straight into the well. Without it, water sheds off the edge and down along the foundation.
Do Curved Window Wells Need A Different Approach?
Measure at the widest point and use the largest reading. Curved wells rarely hold a constant width, so a cover cut to a single centerline measurement will leave gaps along the outer bend. Take two or three readings across the curve and order to the biggest one, rounding up if you are between stock sizes.
References & Sources
- InterNACHI. “Window Well Inspection.” Supports egress area requirements and window well inspection guidance.
- Window Well Experts. “Measuring Guide for Covers.” Supports measuring method, flange handling, stock sizes, and material options.
- Lowe’s. “How to Install a Window Well Cover.” Supports overhang and installation fit checks.
