Enter your Catchment Area, Rainfall Depth, and Runoff Coefficient into the Rainfall Volume Calculator to find your Total Rainwater Volume — plus a full breakdown across Cubic Feet, Liters, and Collection Efficiency so you know exactly how much water you're actually capturing.
Total Rainwater Volume
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Volume (Cubic Feet)
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Volume (Liters)
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Collection Efficiency
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Rainfall volume is calculated using the formula: Volume = Catchment Area × Rainfall Depth × Runoff Coefficient. This gives you the total amount of water collected from rain falling on a given area.
The runoff coefficient represents the efficiency of water collection from different surfaces. Smooth surfaces like roofs have coefficients around 0.8-0.9, while grass and soil have lower coefficients around 0.3-0.5.
For every inch of rainfall, you can collect approximately 0.623 gallons per square foot of roof area. A 1,000 sq ft roof can collect about 623 gallons from 1 inch of rain.
Key factors include catchment area size, rainfall amount, surface material, roof slope, and collection system efficiency. Losses occur due to evaporation, absorption, and system inefficiencies.
Meteorologists use rain gauges - cylindrical containers that collect rainwater. The depth is measured in inches or millimeters, representing how deep the water would be if it didn't run off.
Yes, adjust the runoff coefficient based on your surface: concrete/asphalt (0.9), metal roof (0.85), tile roof (0.8), gravel (0.6), grass (0.3), or forest (0.2).
Rainfall depth measures how deep water would be on a flat surface (inches/mm), while volume measures the total amount of water collected (gallons/liters) from a specific catchment area.