Snow Water Equivalent
Calculator
Results
- Snow water equivalent (mm)
- 40
- Snow-to-water ratio
- 10
- Water per square metre (L/m²)
- 40
Weather results
| Snow water equivalent (mm) | 40 |
| Snow-to-water ratio | 10 |
| Water per square metre (L/m²) | 40 |
formula-map diagram
- Snow water equivalent (mm)
- 40
- Snow-to-water ratio
- 10
- Water per square metre (L/m²)
- 40
Weather relationship
Formula
SWE (mm) = depth (mm) × ρ_snow ÷ ρ_water, ρ_water = 1000 kg/m³= 40
Note
This is a simplified model: it applies the published standard formula to the numbers you entered and ignores local terrain, radiation, precipitation type and instrument error. Wind chill is the 2001 NWS/Environment Canada regression, valid at or below 10 °C with wind at or above 4.8 km/h; the heat index is the Rothfusz regression, reliable above about 27 °C; dew point uses the Magnus approximation (a = 17.27, b = 237.7 °C) over liquid water; wet bulb uses Stull's approximation at standard sea-level pressure; pressure and density altitude assume the International Standard Atmosphere and dry air. Do not use these results for aviation, structural or safety decisions without an official forecast or a qualified professional.
More in Weather and climate
See all →Frequently asked questions
What is snow water equivalent (SWE) and why is it more useful than snow depth alone?+
SWE is the depth of liquid water that would result if a given snowpack were completely melted. Snow depth alone doesn't tell you how much water is actually stored in it, since snow density varies enormously depending on how wet, compacted, or fresh it is.
How is SWE calculated from snow depth?+
SWE equals snow depth multiplied by the snowpack's density ratio relative to water (its specific gravity). Fresh, dry powder might have a density ratio around 0.05-0.1 (so 10 inches of powder yields roughly 0.5-1 inch of water), while wet, compacted, or old spring snow can be 0.3-0.5 or higher.
Why does snow density vary so much between storms?+
Snow density depends heavily on air temperature at the time of the snowfall (colder air generally produces lighter, drier flakes), wind (which can compact snow as it falls), and how much time has passed since the snow fell, since snowpack settles and densifies over time even without melting.
Why do water managers and forecasters care about SWE specifically?+
Reservoir and flood planning depends on how much actual water is stored in the mountain snowpack, not on how many inches or centimetres of snow are on the ground, since a shallow but dense snowpack can hold more water than a deep, fluffy one.
Can two locations with identical snow depth have very different flood risk when it melts?+
Yes, exactly because SWE, not depth, determines melt-driven water volume. A location with 50 cm of light, fresh powder and another with 50 cm of dense, wet spring snow can differ in stored water content by a factor of five or more.