Step 1: Enter the length in feet of your drainage area Enter the width in feet of your drainage area Step 2:  Select the surface of your Drainage Area Concrete Asphalt Roof Top Gravel-Compact Clay-Bare Clay-Lt. Vegetation Clay-Dense Vegetation Gravel-Bare Gravel-Lt. Vegetation Gravel-Dense Vegetation Loam-Bare Loam-Lt. Vegetation Loam-Dense Vegetation Sand-Bare Sand-Lt. Vegetation Sand-Dense Vegetation Grass Area Step 3:  Select the material used as backfill Gravel-Compact Clay-Bare Clay-Lt. Vegetation Clay-Dense Vegetation Gravel-Bare Gravel-Lt. Vegetation Gravel-Dense Vegetation Loam-Bare Loam-Lt. Vegetation Loam-Dense Vegetation Sand-Bare Sand-Lt. Vegetation Sand-Dense Vegetation Grass Area Step 4:  Enter the diameter in feet of the backfill material Step 5:  Select the soil type under the Flo-Well Gravel-Compact Clay-Bare Clay-Lt. Vegetation Clay-Dense Vegetation Gravel-Bare Gravel-Lt. Vegetation Gravel-Dense Vegetation Loam-Bare Loam-Lt. Vegetation Loam-Dense Vegetation Sand-Bare Sand-Lt. Vegetation Sand-Dense Vegetation Grass Area Step 6: Press the Calculate button for results Step 7: View your results below   Formulas: Number of Flo-Wells to use per Drainage Area = [Water Runoff Volume into Flo-Well] X Coefficient of Ground Under Flo-Well] [Volume of Flo-Well (7.527ft3)] + Volume of Backfill Material] Water Runoff Volume = (Sq. Ft. Area X Coefficient of Runoff) 12 Volume of Backfill Material = 3.14/4 X (Diameter of Backfill Material2 - Diameter of Flow-Well2) X Depth of Flow-Well X (1-Coefficient of Runoff for Backfill Material)