The catchment area is the area from which rainfall is collected. If you are using the roof of a building for this purpose, calculate the square footage of this area by taking the length of the building, including the overhang(s) and multiply this by the width measurement plus the overhang(s) of the building.

Example:

Rainfall = 2" per square foot
square footage of catchment area = 2000 sq ft
you won't be able to collect 100% of the water
this catchment area is 80% efficient, meaning you will lose 20% of the water
the amount of rain and the square footage has to be in the same measurements.

convert the area in square feet to square inches to be able to do the calculation

converting square footage to square inches: there are 144 sq inches in one square foot

2000 * 144 = 288000 sq inches = 288000 * 2 = 576000 cubic inches of water. There are 231 cubic inches in one US gallon -- 576000 / 231 = 2494 US gallons of water @ 100% efficiency @ 80% -- 2494 * (80 ÷ 100) = 1995.2 US gallons of water @ 80% efficiency

Calculation

1. rainfall amount, measured in inches per square foot
2. total square footage of the catchment area
3. efficiency (preset @ 80%)

Results

the amount of water collected from the catchment area in

1. cubic inches
2. US gallons
3. Imperial gallons
4. litres

Cisterns, Tanks and Rainwater Harvesting

• Capacity of a Round Cistern - Imperial measurements
• Capacity of a Round Cistern - Metric measurements
• Capacity of a Square or Rectangular Shaped Cistern - Imperial measurements
• Capacity of a Square or Rectangular Shaped Cistern - Metric measurements
• Collecting Rain Water from a Catchment Area/ Inch per Square Foot
• Rainfall per Unit Area, Inch per Acre
• Rainfall per Unit Area, Millimetres per Acre
• Rainfall per Unit Area, Millimetres per Hectare

Water Flow Rate Calculators

• Garden Hose Flow Calculator
• Measuring the Water Flow from a Tap in Gallons per Minute
• Measuring the Water Flow from a Tap in Litres per Minute
• Water Application Rate for an Area

Water Pressure and Friction Loss

• Pressure Loss in Pipes from Friction
• Valves and Fittings 1/2" to 24" diameter, equivalent length calculation

Conversions

• Decimal Foot to Decimal Inch - Decimal Inch to Decimal Foot
• Decimal Inch and Foot to Metres and Millimetres

New

• Cistern Fill and Empty Time
• Cistern Fill and Empty Time - Metric