Rain to Snow Calculator
Convert a rainfall amount into the snow depth it would produce at a given temperature, using standard snow-to-liquid ratios.
🌍 What is Rain to Snow Conversion?
Rain to snow conversion answers a question every winter forecast has to answer: if this much precipitation falls as liquid water, how deep will the snow be? The link between the two is the snow-to-liquid ratio, usually written as SLR and quoted as something like 10 to 1 or 20 to 1. It is the depth of fresh snow divided by the depth of water that snow melts down to. Multiply the liquid amount by the ratio and you have the snow depth. Divide instead, and you go the other way, from a measured snow depth back to its water content.
This conversion turns up constantly in practical winter work. Broadcast meteorologists use it to translate a model's quantitative precipitation forecast into the snow totals viewers actually care about. Highway and airport crews use it to plan plough routes and de-icing chemical volumes, since 30 cm of light powder and 30 cm of wet cement snow need very different equipment. Roof engineers use the reverse direction to convert an observed snow depth into a structural load, because load depends on water mass, not on depth. Hydrologists tracking snowpack use it to estimate how much spring runoff is stored in a mountain basin, and ski resorts use it to judge whether an incoming storm will deliver skiable powder or a heavy base layer.
The biggest misconception is that the familiar 10 to 1 rule is universal. It is not. Ten to one is a reasonable approximation only close to the freezing mark, where partly melted crystals pack together densely. Analyses of long-term United States snowfall records find an overall average nearer 13 to 1, and individual events span roughly 3 to 1 for sleet-contaminated wet snow up to well over 50 to 1 for very cold continental powder. A second misconception is that surface temperature alone determines the ratio. Crystal habit in the cloud, wind speed at the surface, and the depth of the dendritic growth zone all matter, which is why this calculator also lets you enter a ratio directly when you have a better estimate.
This calculator gives you both routes. Leave it on the temperature tab and it selects the ratio from the standard band table used in operational forecasting, or switch to the custom tab and supply your own SLR. Either way it reports the snow depth in centimetres and inches, the ratio it applied and the liquid water equivalent, plus a chart showing how the snow depth for your rainfall amount would change across the whole temperature range.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — Wet Snow Near Freezing
10 mm of rain at −1°C
Example 2 — Cold Powder Snowfall
25 mm of rain at −12°C
Example 3 — Imperial Units, Very Cold Air
0.4 inches of rain at 5°F
Example 4 — Custom Measured Ratio
20 mm of rain with a measured 12:1 ratio
❓ Frequently Asked Questions
🔗 Related Calculators
How much snow does one inch of rain make?
It depends on temperature. Near freezing, around 28 to 34 degrees Fahrenheit, one inch of rain equals roughly 10 inches of snow. At 10 to 15 degrees Fahrenheit the ratio rises to about 30 to 1, so the same inch of liquid would produce about 30 inches of snow.
What is the snow-to-liquid ratio?
The snow-to-liquid ratio, or SLR, is the depth of freshly fallen snow divided by the depth of water it melts down to. A 10 to 1 ratio means 10 cm of snow melts to 1 cm of water. It is the single number that converts a precipitation forecast in liquid terms into a snow depth.
What temperature gives a 10 to 1 snow ratio?
Roughly 28 to 34 degrees Fahrenheit, or about minus 2 to plus 1 degrees Celsius. This is the wet, heavy snow regime where crystals partly melt and pack together tightly, giving the lowest ratios and the heaviest shovelling.
Why does colder air produce more snow from the same rainfall?
Colder air produces smaller, drier crystals that interlock loosely with a great deal of trapped air, so the same mass of water occupies far more depth. Warm snow near freezing has a wet surface film that lets crystals collapse together into a dense layer instead.
What is the snow-to-liquid ratio table used here?
34 to 28 F gives 10 to 1, 27 to 20 F gives 15 to 1, 19 to 15 F gives 20 to 1, 14 to 10 F gives 30 to 1, 9 to 0 F gives 40 to 1, minus 1 to minus 20 F gives 50 to 1, and below minus 20 F gives 100 to 1. Above 34 F precipitation stays liquid and no snow accumulates.
Can I enter my own snow-to-liquid ratio?
Yes. Switch to the Custom ratio tab and type any ratio you like. Use this when a forecast product publishes an SLR directly, or when you have measured the ratio yourself by melting a snow core of known depth.
How do I measure snow-to-liquid ratio at home?
Push a straight-sided container down through fresh snow to collect a core of known depth, melt it indoors, then measure the water depth in the same container. Divide the original snow depth by the melted water depth to get the ratio.
Is the 10 to 1 rule accurate?
Only near the freezing mark. Studies of United States snowfall observations find average ratios closer to 13 to 1 overall, with individual events ranging from about 3 to 1 for sleet-laden wet snow to over 50 to 1 for very cold interior powder. Treating 10 to 1 as universal badly underestimates cold-region snowfall.
Does wind change how much snow accumulates?
Yes. Wind breaks falling crystals into smaller fragments and packs them down, which lowers the effective ratio, often by a third or more in an exposed location. The same storm can leave deep drifts in a sheltered yard and a thin wind-packed crust on an open field.
What is snow water equivalent?
Snow water equivalent, or SWE, is the depth of water you would get by melting a snow column. It is the liquid figure this calculator starts from, and hydrologists track it because spring runoff depends on the water stored in the snowpack, not on how deep the snow looks.
Why does no snow show above 34 degrees Fahrenheit?
Above about 34 F the near-surface air is warm enough that falling crystals melt on the way down and any that reach the ground melt on contact, so nothing accumulates. The calculator reports no snow rather than a misleading small depth.
Can I use this to convert snow back to rainfall?
Indirectly. Divide your measured snow depth by the ratio for that temperature to get the liquid equivalent. For example 60 cm of snow that fell at 5 degrees Fahrenheit, a 40 to 1 regime, corresponds to only 1.5 cm of liquid water.