Quick answer
Snow water equivalent SWE = snow depth × snow density ÷ water density. 12 inches of snow at 10% density holds 1.2 inches (30.48 mm) of water.
Enter the snow depth and its density as a percent of water. The calculator returns the water equivalent in inches and millimetres.
Related tools: Cooling Degree Days Calculator: Cooling degree days from daily high and low temperatures. Heating Degree Days Calculator: Heating degree days from daily high and low temperatures. Water Viscosity Calculator: Dynamic viscosity of liquid water at a temperature.
How to use the Snow Water Equivalent Calculator
- Enter snow depth (in) (above 0).
- Enter snow density (% of water) (%) (between 0 and 100).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Snow depth | A number, in in | > 0 |
| Snow density (% of water) | A number, in % | > 0, ≤ 100 |
Formula and method
Formula
SWE = snow depth × snow density ÷ water density
IEEE-754 double precision; shown to the decimals indicated.
Density as a percentage of water density; fresh snow is typically much lighter than old snow.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Snow depth = 12; Snow density (% of water) = 10.
| Result | Value |
|---|---|
| Snow water equivalent | 1.2 in |
| In mm | 30.48 |
Example 2
Inputs: Snow depth = 30; Snow density (% of water) = 15.
| Result | Value |
|---|---|
| Snow water equivalent | 4.5 in |
| In mm | 114.3 |
Example 3
Inputs: Snow depth = 8; Snow density (% of water) = 25.
| Result | Value |
|---|---|
| Snow water equivalent | 2 in |
| In mm | 50.8 |
The first line is the headline result (snow water equivalent). Below it the snow Water Equivalent Calculator lists in mm, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
The 10:1 rule
A common rule is 10 inches of snow per inch of water, a density of 10%. Wet, heavy snow may be 20 to 30% and dry powder 5%. Measuring a core sample gives a better density.
Why SWE matters
Hydrologists forecast spring runoff from SWE in the snowpack. 30.48 mm of water over a catchment becomes the same depth of meltwater. Density rises as snow settles.
How the result changes with snow depth
Holding every other input at the first worked example, this table changes only snow depth. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Snow depth | Snow water equivalent | In mm |
|---|---|---|
| 6 | 0.6 in | 15.24 |
| 12 | 1.2 in | 30.48 |
| 24 | 2.4 in | 60.96 |
| 48 | 4.8 in | 121.92 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Snow depth: entering "0" shows "Snow depth must be greater than 0." beside that field and no result.
- Snow density (% of water): entering "0" shows "Snow density (% of water) must be greater than 0." beside that field and no result.
Choosing between the Snow Water Equivalent Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Cooling Degree Days Calculator](/science/cooling-degree-days-calculator/) | base temperature, daily highs and daily lows | Cooling degree days |
| [Heating Degree Days Calculator](/science/heating-degree-days-calculator/) | base temperature, daily highs and daily lows | Heating degree days |
| [Water Viscosity Calculator](/science/water-viscosity/) | temperature | Dynamic viscosity |
| [Water Velocity Calculator](/science/water-velocity-calculator/) | flow and inside diameter | Velocity |
| [Water Runoff Calculator](/science/water-runoff-calculator/) | runoff coefficient, rainfall intensity and drainage area | Peak runoff |
Background: environment and acoustics
Decibels are a logarithmic scale, so sound levels cannot be added arithmetically: two equal sources raise the level by about 3 dB, not double it. Environmental and emissions results depend on the factors behind them (for example the US EPA's equivalency factors), which are averages for a country, fuel and year.
Use the result to compare scenarios rather than as a measured value.
Assumptions and limitations
- Measure density from a core sample
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for snow depth and snow density (% of water) to confirm this.
Frequently asked questions
How do I measure snow density?
Weigh a core of known volume.
What is typical fresh snow density?
Fresh snow is typically 5 to 15% as dense as water; wet, settled snow can be 30% or more.
How is SWE used?
In flood and water supply forecasts.
What does the Snow Water Equivalent Calculator calculate?
Depth of water in a snowpack from snow depth and density. It returns Snow water equivalent and In mm.
What formula does the Snow Water Equivalent Calculator use?
SWE = snow depth × snow density ÷ water density. Density as a percentage of water density; fresh snow is typically much lighter than old snow.
What do I need to enter in the snow Water Equivalent Calculator?
You enter Snow depth (in) and Snow density (% of water) (%).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Measure density from a core sample.
What is an example of a snow Water Equivalent result?
With snow depth 12 and snow density (% of water) 10, the snow water equivalent is 1.2 in.
Where does the method come from?
The method follows: Standard hydrology definition of snow water equivalent.
Related calculators
- Cooling Degree Days Calculator — Cooling degree days from daily high and low temperatures.
- Heating Degree Days Calculator — Heating degree days from daily high and low temperatures.
- Water Viscosity Calculator — Dynamic viscosity of liquid water at a temperature.
- Water Velocity Calculator — Water velocity in a pipe from flow and inside diameter.
- Water Runoff Calculator — Peak runoff by the Rational Method.
Sources
- Standard hydrology definition of snow water equivalent
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.