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Rainfall Volume Calculator
Enter the area and rainfall depth to calculate the total volume of water collected.
m²
mm
How rainfall volume is calculated
Because 1 millimeter of rain falling over 1 square meter deposits exactly 1 liter of water, total volume = area (m²) × rainfall depth (mm). This calculator applies that relationship directly, then converts the result to cubic meters and US gallons.
It’s useful for estimating stormwater runoff, rainwater harvesting potential, or how much water a roof or catchment area collects during a storm.
Last reviewed August 2026