Snow Water Equivalent Calculator
Snow water equivalent (SWE) is the depth of water you would get if a snowpack melted completely in place. It matters for flood forecasting, reservoir management, and avalanche work because two snowpacks of equal depth can hold very different amounts of water. SWE depends on snow density: light, dry powder might be a tenth the density of water, while old wet snow can be a third or more. This tool computes SWE from snow depth and either the snow density (as a fraction of water density) or the snow-to-liquid ratio. Both are user-editable so you can match a measured density or a forecast ratio.
Snow water equivalent formula
SWE = snow depth * snow density fraction
snow-to-liquid ratio = 1 / snow density fraction
Snow density as a fraction of liquid water (which is 1.00 g per cubic centimetre) tells you what share of the snow column is water. Multiply snow depth by that fraction to get the equivalent water depth in the same units. The reciprocal of the density fraction is the snow-to-liquid ratio: a density of 0.10 means a 10 to 1 ratio, where 10 units of snow melt to 1 unit of water.
Worked example
A snowpack is 50 cm deep with a measured density of 0.10 (ten percent of water density, typical of fresh dry snow). SWE = 50 * 0.10 = 5.00 cm of water. The snow-to-liquid ratio is 1 / 0.10 = 10.00 to 1. If that same 50 cm of snow were denser, say 0.30, the SWE would be 15.00 cm, three times as much water from the same depth.
Frequently asked questions
What is snow water equivalent?
Snow water equivalent is the amount of water contained in a snowpack, expressed as the depth of water that would result if the snow melted in place. A 50 cm pack at ten percent density holds 5 cm of water. SWE, not snow depth, drives runoff and flood forecasts because it measures the actual water stored.
How is snow density related to the snow-to-liquid ratio?
They are reciprocals. A snow-to-liquid ratio of 10 to 1 means ten units of snow melt to one unit of water, which is a density of 0.10 relative to liquid water. Fresh cold powder can exceed 20 to 1 (density 0.05), while compacted spring snow may be near 3 to 1 (density 0.33).
What density should I use if I have not measured it?
Fresh dry snow is often around 0.07 to 0.12, settled snow around 0.20 to 0.30, and old wet snowpack 0.30 to 0.50. The most reliable result comes from weighing a measured snow core, which is what snow surveys do. Enter your own measured density when you have it; it is a user-editable input.
Why does snow water equivalent matter?
Water managers and the NRCS snow survey program track SWE across mountain basins to predict spring runoff, fill reservoirs, and warn of floods. Avalanche forecasters use it to assess load on weak layers. For the same snow depth, a higher SWE means more water and more weight.
Official sources
- USDA Natural Resources Conservation Service: Snow Survey and Water Supply Forecasting.
- NOAA National Weather Service: snow and water resources.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.