What is Snow Water Equivalent?
Snow Water Equivalent (SWE) is the amount of liquid water contained within a snowpack. In simple terms, it is the depth of water you would be left with if you instantly melted all the snow in place. SWE is a critical metric for hydrologists, water-resource managers, avalanche forecasters and skiers, because two snowpacks of identical depth can hold very different amounts of water depending on how dense they are.
How to use this calculator
Enter three values: the measured snow depth (in centimeters), the snow density (in kg/m³), and the density of water (default 1000 kg/m³). The calculator multiplies the depth by the density ratio and returns the SWE expressed in centimeters, millimeters and inches, along with the snow-to-water ratio as a percentage. Typical snow densities range from about 50–70 kg/m³ for fresh dry powder up to 400–500 kg/m³ for old, settled or wet snow.
The formula explained
The governing equation is $$\text{SWE} = \text{Snow Depth (cm)} \times \frac{\text{Snow Density}}{\text{Water Density}}$$ Because water has a density of 1000 kg/m³, the term \(\frac{\text{snow\_density}}{\text{water\_density}}\) is the fraction of the snow column that is actually water. Multiplying that fraction by the snow depth collapses the airy snowpack down to its equivalent water depth.
Worked example
Suppose you measure a snow depth of 100 cm with a snow density of 250 kg/m³. The density ratio is \(250 / 1000 = 0.25\), so $$\text{SWE} = 100 \times 0.25 = 25\ \text{cm}$$ of water, which is 250 mm or about 9.84 inches. The snow-to-water ratio is 25%, meaning a quarter of that snow column is water.
FAQ
Why does depth alone not tell me the water content? Because snow is mostly air. A meter of light powder may hold less water than 30 cm of dense, wind-packed snow. Density is what links depth to water.
What density should I use? If you measured it directly, use that. Otherwise use a representative value: ~100 kg/m³ for fresh dry snow, ~250–350 kg/m³ for settled snow, and higher for wet or spring snow.
Can I keep depth in inches? The formula is unit-agnostic for depth — the SWE comes out in the same length unit as your depth input. This tool assumes depth in cm and also converts the result to mm and inches.
