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Rain is a natural phenomenon that everyone is familiar with, but have you ever considered the weight of the rainfall on a particular area? In engineering and environmental science, calculating the rain load – the weight of the rainfall per unit area – is crucial for planning and designing various structures, such as rooftops, canopies, and other structures subject to outdoor weather conditions. This article introduces the Rain Load Calculator, a handy tool to determine the rain load based on the rainfall rate and the area under consideration.

## What is a Rain Load Calculator?

A Rain Load Calculator is a tool that calculates the weight of rainfall on a specified area over a specific period. This tool utilizes the formula for determining rain load, which factors in the rate of rainfall (measured in mm/hr) and the area it falls on (measured in square meters, m²).

The formula used for the calculation of rain load (R) is:

R = Rainfall Rate (mm/hr) * Area (m²) * 1 kg/m³

The constant “1 kg/m³” is derived from the fact that 1 mm of rain falling over 1 square meter is equal to 1 liter of water, which weighs approximately 1 kilogram.

## Working Example

Suppose there’s a rainfall event with a rainfall rate of 20 mm/hr, and you’re interested in the impact on a rooftop that spans 50 m².

The rain load (R) would be:

R = 20 mm/hr * 50 m² * 1 kg/m³ = 1000 kg

This means that 1000 kg of rain is falling on that rooftop every hour during this rainfall event.