Rain Garden Sizing Calculator
Rain Garden Size Calculator
Calculate the required rain garden size for your property
Overflow & Drainage
Calculate overflow volume for extreme rain events
Formula
Garden Area = (Roof Area x Rainfall / 12) / (Ponding Depth / 12) x Soil Factor | Water Volume = Area x Rainfall / 12
Frequently Asked Questions
How big should my rain garden be?
A rain garden should typically be 10-30% of the area draining into it. For a 1,000 sq ft roof, plan for 100-300 sq ft depending on soil type. Sandy soil needs less area (10-15%), clay soil needs more (25-40%).
Where should I place a rain garden?
Place it at least 10 feet from your house foundation, in a naturally low area, and away from septic systems and utilities. Ensure it gets at least partial sun. The garden should be downhill from the water source (roof downspout or driveway).
What plants work best in a rain garden?
Use native plants that tolerate both wet and dry conditions. Good choices include switchgrass, black-eyed Susan, cardinal flower, blue flag iris, and native sedges. Avoid invasive species and non-native plants that may not handle periodic flooding.
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