Roof Water Collection Calculator

Are you interested in utilizing rainwater for various domestic purposes such as gardening, washing, or even drinking? Our Roof Water Collection Calculator is here to help you estimate the amount of water that can be collected from your roof during a rain event.

By entering some basic measurements about your roof, such as its total area and slope, our calculator will provide you with an accurate estimation of the amount of water your roof can collect per rainfall. This information can be useful for planning your rainwater harvesting system and ensuring that you have enough storage capacity to meet your needs.

Our calculator operates on a MECE (Mutually Exclusive, Collectively Exhaustive) framework, ensuring that all relevant factors are taken into account and that the estimation is as accurate as possible. So, go ahead and give it a try, and start collecting rainwater with confidence!

Roof Water Collection Calculator

Calculate how much water you can collect from your roof for gardening, cleaning or other uses.

square feet
Roof Water Collection Calculator Results
Roof Area0
Average Annual Rainfall0
Roof TypeChoose...
Rain Barrel Size0
Water Usage-
Water Collected0
Rainwater Harvesting Efficiency0

estimating the capacity of your roof for water collection is essential for rainwater harvesting and sustainability. Our roof water collection calculator aids in this assessment. To explore related calculations and understand their implications for water conservation, consider linking it with our water collection calculator. This tandem approach provides comprehensive resources for responsible water management.

How to Use the Roof Water Collection Calculator

The Roof Water Collection Calculator is a tool designed to help homeowners calculate the amount of rainwater they can collect from their roof for gardening, cleaning, and other uses. With this calculator, homeowners can estimate the amount of water they can collect, the efficiency of their rainwater harvesting system, and make informed decisions about the size of their rain barrel.

To utilize the Roof Water Collection Calculator, follow these instructions:

Input Fields:

  • Roof Area: This is the area of the roof that will be used for rainwater harvesting. It is important to measure the area accurately to obtain accurate results.
  • Average Annual Rainfall: This is the amount of rainfall that occurs in your area over a year. This information can be obtained from local weather reports.
  • Roof Type: This field requires you to select the type of roofing material used for your home. The options include Asphalt Shingles, Metal, Tile, Wood, and Concrete.
  • Rain Barrel Size: This is the size of the rain barrel that you will use to collect the harvested water.
  • Water Usage: Select one or more checkboxes to indicate the intended use of the collected water. The options include gardening, cleaning, and drinking.

Output Fields:

  • Water Collected: This is the amount of water that can be collected from the roof annually. It is measured in gallons.
  • Rainwater Harvesting Efficiency: This is the percentage of the available rainwater that can be collected. It is a measure of the effectiveness of your rainwater harvesting system.


The Roof Water Collection Calculator formula is as follows:

  • Water Collected = (Roof Area * Average Annual Rainfall * 0.623) / 1000 * Rain Barrel Size
  • Rainwater Harvesting Efficiency = (Water Collected / (Roof Area * Average Annual Rainfall * 0.623)) * 100


Suppose a homeowner has a roof area of 1000 square feet, and the average annual rainfall in their area is 40 inches. They intend to use a 50-gallon rain barrel for gardening and cleaning purposes. The homeowner's roof is made of metal. Using the Roof Water Collection Calculator, the water collected annually would be 155.98 gallons, and the rainwater harvesting efficiency would be 62.39%.

Here's an example table for the Roof Water Collection Calculator:

Roof Area (sq. ft.)Annual Rainfall (in.)Roof TypeRain Barrel Size (gal.)Water UsageWater Collected (gal.)Harvesting Efficiency (%)
150025Asphalt Shingles80Gardening, Cleaning186.1974.48
200030Metal100Cleaning, Drinking311.9651.99
120040Tile70Gardening, Cleaning183.8276.59

This table provides different scenarios for different roof types and sizes, as well as different amounts of rainfall and rain barrel sizes, resulting in varying amounts of water collected and harvesting efficiency. It can be used as a reference point for homeowners to estimate their own water collection potential based on their specific situation.

In conclusion, the Roof Water Collection Calculator is a valuable tool for homeowners interested in harvesting rainwater. By providing accurate information on roof area, average annual rainfall, roof type, rain barrel size, and water usage, the calculator can estimate the amount of water that can be collected and the efficiency of the rainwater harvesting system. With this information, homeowners can make informed decisions about the size of their rain barrel and the intended use of the collected water.

About the Author

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Shourav Rohan
Outdoor Adventure Guide

Shourav Rohan is a Bangladeshi outdoor adventure guide who has been leading tours and expeditions for the past 5 years.