Rainfall Calculator

Calculate how much water falls on a roof or yard during rain.

How the Math Works

The Rainfall Calculator uses a straightforward volume formula where gallons equals depth in feet multiplied by the area in square feet, then multiplied by the conversion factor 7.48052. This conversion factor represents the number of gallons in one cubic foot of water, transforming the volume from cubic feet to gallons. When you input rainfall depth (converted from inches to feet by dividing by 12) and the collection area, the calculator determines the total water volume captured.

Practical Applications

To use this calculator practically, first measure or determine the area where rainfall collects - for example, your roof's catchment area or a rain barrel's collection surface. Measure the rainfall depth, converting inches to feet (1 inch = 0.0833 feet). Input these values directly into the calculator: multiply the depth in feet by your area in square feet, then by 7.48052 to get the total gallons collected. This helps you estimate how much water your rain collection system can capture.

Day-to-Day Use

This calculation helps you plan for water usage, determine if you need larger rain barrels, or calculate irrigation needs for gardens. Homeowners can estimate their water harvesting potential to reduce municipal water bills, while farmers and landscapers can determine irrigation volumes from seasonal rainfall. It's also useful for emergency preparedness, helping you understand how much stored rainwater you have available during droughts or water restrictions.

Worked example

1 in over 1,000 ft² → ~623 gallons.

FAQ