Septic Drain Field Cost Calculator
— How Much Do You Need?

These two terms refer to the same thing. Drain field and leach field are used interchangeably across the country, and they describe the underground system of perforated pipes and gravel that receives wastewater from your septic tank and disperses it into the surrounding soil. Depending on your region, you might also hear it called a leach bed, an absorption field, or a soil absorption system. The name changes by location, but the function stays the same: the gravel around the pipes provides the drainage space that filters the effluent as it moves through the soil below. When you order septic drain field gravel from Hello Gravel, you are getting the same material no matter what your local contractor calls the system.

Clean, washed crushed stone is the standard material for a septic drain field and it must be washed. The gravel is usually in the 3/4 inch to 2.5 inch size range, and it must be free of fines, dust, silt, and clay. Those fine particles clog the gaps between the stones and prevent water from flowing through. The gravel layer should have open void space to allow drainage into the soil below. Angular crushed stone is most common, though some local codes specify rounded river gravel. Local codes vary, so check with your local code office or septic installer. Hello Gravel carries clean, washed stone suitable for drain field use, and if you’re unsure which product fits your project, the Hello Gravel team can help you choose.

The amount you need depends on the length of your trenches, their width, and how deep the gravel layer should be. A typical drain field trench is 18 to 36 inches wide. The gravel layer is usually 12 to 18 inches deep. A practical starting point is 2 feet wide with 12 inches of gravel, which uses about 7 to 8 cubic yards of stone per 100 linear feet. That comes to roughly 9 to 11 tons per 100 linear feet. For a 300 linear foot field, expect around 22 to 24 cubic yards, or about 28 to 34 tons. These are estimates; use the Hello Gravel calculator for a precise number based on your exact trench measurements. It is better to order a little extra than to run short during installation.

A common rule of thumb is 100 linear feet of drain field per bedroom. That suggests about 300 linear feet for a 3 bedroom home and about 400 linear feet for a 4 bedroom home. However, this is only a rough guide. The actual length is determined by a perc test that measures how quickly your soil absorbs water. Sandy or loamy soils absorb faster and may need less field length, while clay soils drain slowly and may require more or a different system design. Your local health department or a licensed septic designer uses the perc test results to size the field. Once you know the total footage required, you can use the Hello Gravel calculator to estimate gravel needs.

The most common cause of drain field failure is a biomat buildup. A slimy layer of bacteria and organic matter forms on the trench surfaces and slows or blocks drainage. This often happens when solids reach the field because the septic tank has not been pumped on schedule. Other causes include heavy equipment driving over the field, tree roots, hydraulic overload from excess water, and damage to pipes. Signs of trouble include slow drains, toilets that gurgle, sewage odors in the yard, soggy ground over the field, or unusually lush grass growing directly above the trenches. If you see these signs, have a licensed septic professional evaluate the system.