To figure out the square footage of a surface, multiply the width x length. The square footage of a roof is the same whether it is pitched or flat. Assuming a depth of 12” to your absorption area, divide the total gallons captured by 7.48 (gallons in a cubic foot of area).

## How is roof rain runoff calculated?

The basic calculation is (a X r)/231=g where “a” is the area of your roof in square feet, “r” is the amount of rain in inches, and “g” is the amount of runoff in gallons.

## How do I calculate how much water is collected from my roof?

For calculation we take the following formula: mean annual rainfall in mm x area in m² x runoff factor = collected rainwater in litres. In our example this means: 450 x 120 x 0.9 = 48 600 litres.

## How do you calculate rainwater volume?

Formula: Area (Length x Width) x Rainfall

- A = Length of the roof area.
- B = Width of the roof area.
- C= The amount of rainfall in inches.
- The formula is A x B x C = Water Volume.

## How do you calculate rainwater harvesting potential?

Rooftop RWH potential is estimated by multiplying the average annual rainfall, roof area and runoff coefficient. Runoff coefficient of the concrete roof is considered in the calculation which typically varies from 0.70-0.80.

## How do you calculate runoff?

Simple, straightforward methods of calculating runoff can tell you the amount of water that storms bring to the earth. For a given surface area such as a roof or yard, multiply the area by the inches of rainfall and divide by 231 to obtain the runoff in gallons.

## How much rain water comes off a roof?

Every square foot of roof space collects . 6 gallons of water in a 1 inch rainfall.

## How many Litres is 1mm of rain?

With a rainfall of 1 mm, every square metre receives 1 litre of rain water. A rainfall of 1 mm supplies 0.001 m3, or 1 litre of water to each square metre of the field. Thus 1 ha receives 10 000 litres.

## How do I calculate the square footage of my roof?

Multiply the length by the width to find the area of rectangular sections.

- If a section is 120 feet (37 m) x 100 feet (30 m), its total square footage would be 12,000 square feet (1,100 m2).
- Be sure to find the area of any dormers on your roof, as well.

## How much rain does it take to fill a rainwater tank?

An average 4 bedroom house has a roof surface area of approx. 200 square metres. So, if you have an average 3 bedroom house and a 3000L tank, it would take 20mm of rain to fill your tank. On average each of us uses 147 litres of water per day.

## What is MM IN RAIN measure?

The most common rainfall measurement is the total rainfall depth during a given period, expressed in millimeters (mm). For instance, we might want to know how many millimeters of rain fell over the course of 1 h, 1 day, 1 month, or 1 year. You can easily get a rough measurement of rainfall depth at home.

## What is the volume of 1 inch of rain?

A standard Weather Service rain gauge is a cylinder eight inches in diameter, so one inch of rain would have a volume of about 28 ounces or about three cups. Measurements of very large volumes of water, such as lakes or reservoirs, are expressed in acre-feet.

## What is a simple method of rainwater harvesting?

Barrel harvesting

It is the simplest method of rainwater harvesting. There is generally a drain on the rooftop or terrace, to which you connect a strong pipeline. Let this pipeline be connected to a large barrel. You can also have multiple barrels if it is a high rainfall receiving area.

## How is rain water harvesting done?

How does rainwater harvesting work? Rainwater harvesting systems capture rainwater by directing it from large surfaces (e.g. roofs) to an underground or over-ground holding tank. The harvested rainwater is filtered and then pumped directly to the appliances or to a header tank.

## What are advantages of rainwater harvesting?

Advantages of Rainwater Harvesting

Decreases the demand for water. Reduces the need for imported water. Promotes both water and energy conservation. Improves the quality and quantity of groundwater.