How to Measure Window Well Cover Size | Get It Right The First Time

Measure window well cover size by taking the well’s widest width and deepest projection, plus clearance if the window sits above the lip.

For the full breakdown, see our best Basement Well Covers guide.

An undersized cover leaves gaps that let in rain, leaves, and pests. An oversized one won’t sit flush against the foundation. The fix is simple: measure the well, not the window, at its widest points. This guide walks through exactly what to record so the cover you order actually fits.

What Measurements Do You Need?

For most standard wells, two numbers cover it: width and projection. Width is the side-to-side opening measured at the foundation wall. Projection is the distance from the wall out to the front edge of the well.

Beyond those basics, three more details matter depending on your setup:

• Height above grade — the distance from the well’s lip down to the ground, relevant for metal wells and low-profile covers.
• Window clearance — if the window sits above the well lip, measure from the lip up to the bottom of the window frame. This prevents the cover from hitting the sash or crank mechanism.
• Wall thickness — for concrete, brick, or wood wells, manufacturers often want inside and outside dimensions because rim thickness changes how the cover sits.

For metal wells specifically, measure outside edge to outside edge, side-to-side and front-to-back. Record to the nearest 1/8 inch — covers mount tight, and a quarter-inch error can mean a gap.

How to Measure Different Well Types

Not every well is a simple rectangle. How you measure depends on the shape and material you’re working with.

Metal Wells

Measure the outer flanges, not the inside opening. Corrugated metal wells are usually wider at the top than at the bottom, and the flanges are what the cover attaches to. Run the tape across the outside edges at the point where the well meets the house for width, then from the wall to the outer front edge for projection.

Concrete, Plastic, Wood, or Brick Wells

For these, both outside and inside dimensions matter because the rim can be thick. Measure the outside-to-outside width where the well touches the foundation, then the inside width. Do the same for depth. AIL’s 2024 v5 sell sheet also asks for the distance from the well lip to the top of the window frame on both the left and right sides, so grab both.

Round, Semicircular, or Irregular Wells

Measure at multiple points and use the widest readings. The Conquest Steel quotation form uses three distinct values for custom covers: Length (the opening where the well attaches to the house), Projection (wall to the outside front), and Front Length (the flat section between the front corners). If your well has a rounded front, note that and add a sketch.