Drainage Calculator
— How Much Do You Need?

Drainage gravel is a clean, washed stone with no fine particles, dust, or clay mixed in. That single distinction separates it from most other aggregates. Base gravels and compactable fills are designed to pack tightly; fines fill the voids and help them harden. Drainage gravel stays loose and porous, so water moves through the gaps between the stones quickly. Common options include #57 crushed stone (about 3/4 inch to 1 inch), #89 stone (around 3/8 inch), and washed pea gravel. The right choice depends on how fast you need water to move, how deep the system runs, and whether it needs to support weight above it. Using the wrong material can make a drainage system slow or ineffective. Choose the right stone from the start for decades of reliable performance.

The most obvious sign is standing water. Puddles that last more than 24 hours after a rain indicate your soil is not draining quickly enough. Ground that stays soft or soggy between rain events is another indicator. Water stains or damp spots on basement walls suggest water is pooling against the home rather than draining away. Erosion channels or gullies in the yard show where runoff is moving too fast. Mulch washing out of beds and soil pulling away from the foundation are also signs. If you see these, a drainage fix with bulk gravel can help redirect water where it belongs.

Several effective systems depend on clean bulk aggregate. A French drain uses a perforated pipe surrounded by gravel buried in a sloped trench. Water filters through the gravel into the pipe and flows to a safe outlet. A gravel swale is a shallow, sloped channel filled with stone that guides runoff to a lower outlet. A dry creek bed channels water across a yard with rounded gravel for a natural look. Downspout drainage systems use gravel filled trenches or dry wells to absorb roof runoff. Perimeter drains around foundations also rely on coarse drainage stone. All of these require clean, washed aggregate to function well.

Move water away from the foundation by intercepting it before it reaches the building. A common approach is a sloped gravel trench drain along the house, lined with filter fabric, and filled with drainage stone. Water then flows into the trench and away from the foundation. For downspouts, bury a perforated pipe underground, surround it with drainage gravel, and direct water to a yard outlet or dry well. Swales or dry creek beds can carry runoff across the yard, but slope is key. Aim for at least a 1 percent grade, which is about 1 inch of drop per 8 feet of run, so water keeps moving.

A French drain is a buried, sloped trench that carries water away from a problem area. It uses a perforated pipe at the bottom, surrounded by clean drainage gravel, and wrapped in filter fabric to keep soil out. Water seeps into the trench, enters the pipe, and moves downhill to a daylight outlet or other discharge. Typical residential trench is 12 inches wide and 18 to 24 inches deep. For a 100-foot run, expect roughly 4 to 6 tons of clean 3/4-inch crushed stone, depending on pipe space. Longer runs or deeper trenches require more material. The standard choice for most French drains is #57 stone, which is 3/4 to 1 inch and stays open for water flow.