Calculate rain garden size, runoff volume, ponding depth, drainage area, soil infiltration time, plant count, mulch, amended soil, and estimated cost. Use this rain garden calculator for roof runoff, driveway runoff, yard drainage, stormwater control, native planting beds, and landscape water management.
Rain garden size:
The calculator estimates runoff volume from drainage area, rainfall depth, runoff coefficient, and capture goal, then divides by ponding depth.
Runoff volume:
Enter roof, driveway, patio, lawn, or mixed drainage area to estimate gallons of runoff from a storm.
Drain time:
Enter ponding depth and soil infiltration rate to estimate how long water may remain in the garden.
Materials:
Use the garden size to estimate plants, mulch, amended soil, and rough project cost.
A rain garden calculator helps estimate how large a rain garden should be to capture and infiltrate stormwater runoff.
It can be useful for roof downspouts, driveway runoff, patio runoff, low yard areas, landscape drainage, native plant beds, stormwater projects, and erosion control planning.
Your result shows estimated rain garden area, runoff gallons, runoff cubic feet, required ponding storage, planned garden area, drain time, plants needed, mulch volume, amended soil volume, and estimated material cost.
A simple estimate is to calculate runoff volume from the drainage area and rainfall depth, then divide that volume by the planned ponding depth.
Many rain gardens use a ponding depth of about 4 to 8 inches, but the best depth depends on site slope, soil drainage, plants, safety, and local guidance.
Rain gardens are commonly planned to drain within about 24 to 48 hours, but local conditions and design guidelines may vary.
Yes, roof runoff is a common rain garden source, but the garden should be placed where overflow will not damage the foundation, basement, neighbors, sidewalks, or utilities.