Snow Water Equivalent Calculator
Calculate how much liquid water is contained in a given depth of snow.
Essential for hydrology, agriculture, and flood risk assessment.
What is Snow Water Equivalent (SWE)?
Snow Water Equivalent (SWE) is the depth of liquid water that would result if a column of snow were completely melted. It is one of the most important measurements in hydrology, water resource management, and flood forecasting — because snowpack stores large amounts of water that is released gradually during spring melt.
Why snow density varies
Not all snow has the same water content. The ratio of snow depth to water depth depends on the density of the snow, which varies with temperature, age, and weather conditions:
- Freshly fallen light snow (–10°C or colder): very low density, ratio approximately 20:1 (20 cm of snow = 1 cm of water)
- Average snow (–5°C to –10°C): ratio approximately 12:1 to 15:1
- Wet, heavy snow (near 0°C): ratio approximately 5:1 to 8:1
- Settled/compacted snow: ratio approximately 4:1 to 6:1
- Old granular snowpack: ratio approximately 3:1 to 4:1
The formula
SWE (mm) = Snow Depth (mm) ÷ Snow-to-Water Ratio
For example, 30 cm of fresh light snow at a 20:1 ratio contains only 15 mm (1.5 cm) of water. But 30 cm of wet heavy snow at a 5:1 ratio contains 60 mm (6 cm) of water — four times as much.
Practical applications
Farmers use SWE to estimate soil moisture and irrigation needs in spring. Emergency managers use it to forecast runoff and flood risk. Ski resorts use it to assess snow quality and base depth. Water utilities use seasonal snowpack SWE to predict reservoir inflows.