Rain garden calculator

Rain garden sizing chart

The below form will help you properly size your rain garden

What type of soils are you using?

Amended soils or Bioretention media Native soils

What is the amended or replacement soil infiltration rates
Between 45-100mm/hr (1 ¾ in. /hr – 4 in./hr)? 100mm/hr (4 in./hr) or higher

What is your infiltration rate?

See Chapter 4 Site Inventory and Analysis Subsection 4.4.5 Growing Medium for instruction on calculating infiltration rates
15mm/hr (1/2in./hr) or less 15mm/hr – 45 mm/hr (1/2in./hr – 1 ¾ in./hr) 45mm/hr – 100 mm/hr (1¾ in. /hr – 4 in./hr) 100 mm/hr (4 in./hr) or higher

To calculate rain garden size:
Enter your Drainage Area (m² or ft.²) x

(m² or ft.²) Rain Garden Footprint

Note: Calculation for rain garden size is a ratio derived from the Toronto Region Conservation Authority and Credit Valley Conservation LID Design Guide. It factors in a fixed depth of the rain garden, infiltration rates of native soils, void space ratio of growing medium and 24 hr period for runoff to be absorbed by the rain garden. For more details see Chapter 4 Section 4.5 Bioretention in the LID Design Guide.