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This french drain calculator turns a trench length, width, and depth into cubic yards of stone and a matching pipe length. Switch to the drainage calculator for peak runoff: coefficient times rainfall intensity times acres. Both are planning estimates, not a civil design.
Gravel volume
3.70cu yd
Planning estimate from the numbers you enter. Coverage, density, waste and price are assumptions, not a supplier quote or an engineering specification.
How it works
A 50 foot trench, 12 inches wide and 24 inches deep, is 50 times 1 times 2, divided by 27, or 3.70 cubic yards. The pipe length is the 50 feet you typed. The drainage calculator example, a 0.40 coefficient, 2 inches per hour, and 0.50 acres, is 0.400 cubic feet per second, about 179.5 gallons per minute. The rational method is Q = C × i × A, with A in acres and i in inches per hour. It is a peak-flow sketch. It does not route a pipe network or check a percolation rate.
Formula
Runoff in cubic feet per second = coefficient × inches per hour × acres. Gallons per minute are that flow times 448.8. The french drain calculator does not subtract the pipe from the stone.
Example
Gravel is 3.70 cubic yards and the pipe is 50 feet. The drainage calculator example on the other mode is 0.400 cubic feet per second.
Tips
A 4 inch pipe in a 12 inch trench still wants stone around it. If the spoils swell, use the excavation calculator's bulking factor for the haul volume. This page is the hole you fill.
Equipment
Dengaro arranges financing for an excavator or a trencher. Stone yards are not a loan amount.
Important questions
The trench volume is the whole hole. The pipe displaces a little stone. For a small pipe, that difference is usually left in as extra.
Type the one for the surface. A roof is high. A lawn is lower. This page will not assign a C factor for you.
No. It is a peak-flow estimate for the area and intensity you enter. A pipe size still needs slope and a friction check.
Not here. Take the cubic yards to the gravel calculator if you want tons and a price you enter.
Financing built into the sale