Rain Garden Size
150 sq ft
Plants Needed
172
Drain Time
11.5h
Total area of roof, driveway, or patio draining to garden
1" captures ~90% of storms in most US regions
Recommended: 6" for loam soil (range 3"–6")
Rain Garden Size
150
square feet
Water Captured
561
gallons
Drain Time
11.5h
Within 48h limit
Total: 172 plants across 3 moisture zones
DIY: $450–$1,200 ($3–$8/sqft)
Pro: $1,500–$3,000 ($10–$20/sqft)
Design Tips
Inputs
Result
A 1,000 sq ft roof with 0.90 runoff coefficient in loam soil needs a 150 sq ft rain garden with 6-inch ponding depth. The garden captures 562 gallons per 1-inch storm.
Inputs
Result
A 500 sq ft driveway on sandy loam needs only 75 sq ft of rain garden. Fast drainage means the garden empties in under 6 hours.
Inputs
Result
Clay soil requires a much larger garden with shallower ponding. At 3-inch depth, the 600 sq ft garden still drains within the 48-hour limit despite slow clay infiltration.
A rain garden typically needs to be 5-10% of the drainage area it serves. For a 1,000 sq ft roof draining to sandy soil with 6 inches of ponding depth, you need about 150 sq ft of garden. Clay soils with 3-inch ponding require larger gardens.
| Soil Type | Infiltration Rate | Recommended Ponding | Garden Size Factor |
|---|---|---|---|
| Sandy | 8.27 in/hr | 6 inches | ÷ 20 |
| Loam | 0.52 in/hr | 6 inches | ÷ 10 |
| Clay | 0.09 in/hr | 3 inches | ÷ 5 |
A runoff coefficient measures what fraction of rainfall becomes runoff rather than soaking into the ground. Hard surfaces like roofs (0.90) send 90% of rainfall as runoff, while lawns on sandy soil (0.10) only contribute 10%.
| Surface | Coefficient | Runoff from 1" Rain (1000 sqft) |
|---|---|---|
| Roof | 0.90 | 562 gallons |
| Driveway | 0.90 | 562 gallons |
| Lawn (clay) | 0.30 | 187 gallons |
| Lawn (sandy) | 0.10 | 62 gallons |
Plant density varies by moisture zone. The wet center needs 1.5 plants per sq ft, the middle zone needs 1.0, and the dry edges need 0.75. A 150 sq ft garden needs about 165 plants total.
| Zone | Area Share | Density | Plants for 150 sqft Garden |
|---|---|---|---|
| Wet Center | 40% | 1.5/sqft | 90 plants |
| Middle | 35% | 1.0/sqft | 53 plants |
| Dry Edge | 25% | 0.75/sqft | 28 plants |
DIY rain gardens cost $3-$8 per square foot for materials (soil amendments, plants, mulch). Professional installation runs $10-$20 per sq ft. A typical 150 sq ft residential garden costs $450-$1,200 DIY or $1,500-$3,000 professionally installed.
| Garden Size | DIY Cost | Professional Cost |
|---|---|---|
| 100 sq ft | $300–$800 | $1,000–$2,000 |
| 200 sq ft | $600–$1,600 | $2,000–$4,000 |
| 300 sq ft | $900–$2,400 | $3,000–$6,000 |
Most rain gardens are designed to capture 1 inch of rainfall, which handles approximately 90% of storm events in the US. In wetter climates like the Pacific Northwest, you may want to size for 1.5–2 inches.
| Region | Design Rainfall | % Storms Captured |
|---|---|---|
| Most US | 1.0 inch | ~90% |
| Arid West | 0.75 inch | ~90% |
| Pacific NW | 1.5 inches | ~85% |
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Last Updated: Mar 9, 2026
This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.