BuildMeter guide · Excavation & Drainage
Window Well Drainage Gravel Guide
Measure a gravel bed and optional drain column while recognizing that gravel quantity alone cannot solve grading, drain connection or waterproofing problems.
Direct answer
What to know first
Calculate the gravel bed as length × width × depth and add any separately defined gravel-filled drain column. Keep the finished gravel below the window opening, but verify the complete drainage route, grading, cover, waterproofing and egress requirements before relying on the well.
Open Window Well Gravel CalculatorCalculate the defined gravel zones
Measure the gravel bed beneath the well as length × projection × depth. If the detail includes a gravel-filled vertical column, calculate that cylinder separately and add it. Multiply by the number of equal wells, then add a settlement and handling allowance.
| Element | Question to confirm |
|---|---|
| Surface gravel bed | What finished depth and elevation are specified? |
| Drain or gravel column | Where does collected water discharge? |
| Window sill clearance | Will gravel remain below the opening? |
| Well cover and grading | How is roof and surface runoff kept out? |
| Egress dimensions | Does the completed well preserve required access? |
Worked example
Four wells each have a 4 × 2.5 ft bed that is 6 in. deep. Bed volume is 20 ft³ total. Adding four gravel columns 8 in. in diameter and 2 ft deep adds about 2.8 ft³. With 12% allowance, the order is about 25.5 ft³, or 51 half-cubic-foot bags.
Gravel is only one part of drainage
A loose aggregate bed can temporarily receive water, but it does not create an outlet in slow-draining soil. The complete detail may connect to foundation drainage, a dry well or another approved discharge. Foundation waterproofing and surface grading remain critical.
Common mistakes
- Filling gravel above the window sill.
- Assuming gravel alone provides unlimited drainage.
- Directing downspouts toward the well.
- Blocking an egress route with a cover or deep fill.
- Ignoring inspection requirements before backfill.
Use the calculators
Use the Window Well Gravel Calculator for bags and weight, the French Drain Gravel Calculator for connected drain stone and the Excavation Calculator for the soil removal.