Window Well

This calculator treats an egress window well as a rectangular prism: it adds 12 inches of clearance to your Window Width to get the well's actual width, multiplies that by Projection and Depth, and converts the result from cubic inches to cubic feet. Because the well width is your Window Width plus a fixed 12-inch offset rather than a direct multiple of it, Window Width has slightly less leverage over the total volume than Projection or Depth do -- widening the window by 10% only widens the well by a bit less than 10%, since the added 12 inches stays fixed, while a 10% change in Projection or Depth passes through to volume at the full 10%. All three dimensions still increase volume when you increase them; the difference is only in how strongly each one moves the total.

Drainage Stone is a rough rule-of-thumb weight of 100 lbs per cubic foot of well volume, covering the crushed stone typically placed at the well bottom for drainage -- it scales in exact proportion to Volume, so anything that changes the well's volume changes the stone estimate by the same percentage. This is a simple prism approximation; it does not account for a curved or tapered well wall, nor for the additional stone some installers add beneath a drain line.