Window Well Calculator
— How Much Do You Need?

A window well is a curved or rectangular barrier installed around a basement window that sits below ground level. It holds back the surrounding soil so the window stays clear, functional, and able to let in natural light. Without a window well, the earth would press directly against the window frame, leading to moisture damage, cracked glass, and blocked light. Gravel is a critical part of every window well setup because water naturally collects in that excavated space. Rain, runoff, and groundwater all flow toward your foundation and into the well. Without a coarse gravel layer at the bottom, that water has nowhere to go. It pools against the window frame, seeps through gaps, and can eventually cause basement leaks, rot, and mold. Gravel bed lets water percolate down and away from the window rather than rising up against it. Think of it as the foundation of your window well's drainage system. Without gravel, even a well-built window well will eventually cause you problems.

The best gravel for a window well is clean, coarse, and washed. You need material with very few fine particles, meaning minimal dust, clay, or silt. Fine particles clog the spaces between stones over time and slow down drainage, which defeats the whole purpose of putting gravel there in the first place. Two of the most reliable choices are pea gravel and clean washed crushed stone in the 3/4 inch range. Pea gravel is rounded, easy to work with, and has a tidy appearance that looks good if your window well is visible from a patio or walkway. Washed crushed stone in the 3/4 inch size creates excellent drainage because its angular shape leaves plenty of open space for water to move through quickly. In both cases, the word "washed" matters. Washed gravel has had the fines rinsed away, so it stays open and free-draining for years. If you are not sure which product best fits your drainage setup, reach out to the Hello Gravel team and we will help you find the right match.

Soil holds water. Gravel drains it. That difference is the entire reason gravel belongs at the bottom of a window well and soil does not. When soil gets wet, it compacts and becomes dense. Water stops moving through it and instead sits against your foundation wall and window frame. That trapped moisture works its way into your basement, encourages mold growth, and causes long-term structural damage. Using dirt in a window well is one of the most common and costly mistakes homeowners make. Gravel works the other way. Its open, porous structure allows water to pass through almost immediately and percolate down toward the soil below the well or into a drain pipe. It does not compact the way soil does, and it stays effective through many seasons of rain and snow. If you currently have soil or compacted fill in your window wells, replacing it with clean drainage gravel is a straightforward fix that can make a noticeable difference in how dry your basement stays.

Most building codes and installation guides recommend a minimum of 6 inches of gravel at the bottom of a window well. That gives you a solid drainage buffer for typical rain events. In areas with heavy rainfall, high water tables, or clay-heavy soil that drains slowly, going to 12 inches of gravel gives you extra capacity and peace of mind. If your window well connects to a drain pipe or a larger drainage system, 6 inches of gravel over the drain inlet is generally enough to filter sediment and keep the drain flowing freely. If there is no dedicated drain and you are relying entirely on the gravel bed to absorb and slowly release water, the deeper you go the better. A good rule of thumb is this: more gravel depth means more storage capacity during a heavy downpour. When in doubt, add a few extra inches. It is inexpensive insurance against a wet basement.

The total amount depends on the number of window wells you have, their width and depth, and how thick you want the gravel layer to be. A standard window well is roughly 3 to 4 feet wide and extends 18 to 24 inches out from the foundation wall. With a 6 to 12 inch gravel layer at the bottom, each well takes a relatively modest volume of material. That said, most homeowners order window well gravel alongside other materials for a broader project. If you are working on foundation drainage, a French drain, or landscaping at the same time, ordering a bulk truckload through Hello Gravel covers all of it in a single delivery and saves you the hassle of multiple orders. The easiest way to get a precise number is to plug your window well dimensions and desired gravel depth into the Hello Gravel calculator. It will give you a clear material estimate based on your actual project. If you have questions about quantities or want help planning an order that covers your full list of drainage work, our team is always glad to help.