Rain to Snow Calculator

What is the rain-to-snow ratio?

The snow-to-rain ratio (also called the snow ratio or snow liquid ratio) tells you how many units of snow depth result from one unit of liquid water. Fresh snow is mostly air, so a small amount of rain-equivalent water can pile up into a much deeper layer of snow. A ratio of 10 means that 1 mm of rain would fall as roughly 10 mm of snow — the common rule-of-thumb average.

This calculator takes a rainfall amount and a snow-to-rain ratio and returns the equivalent snowfall depth. Enter the rain in millimetres, centimetres, or inches; the snow output can be shown in any of the same units.

How does the calculator work?

Snowfall depth is simply the rainfall (the liquid-water equivalent) multiplied by the ratio. The calculator converts your rainfall to millimetres internally, multiplies by the ratio, and reports the result in your chosen snow unit.

The 10:1 ratio is only an average. In practice it varies with temperature and how the snow forms: cold, dry “powder” can exceed 20:1, while wet snow near freezing may be closer to 5:1 or 8:1. Adjusting the ratio lets you model these conditions.

Formula

$S = R \times r$

where $S$ is the snowfall depth, $R$ is the rainfall (liquid-water equivalent), and $r$ is the snow-to-rain ratio. Both $S$ and $R$ are expressed in the same length unit.

Worked examples

Example 1 — average conditions. With $R = 10\ \text{mm}$ of rain and a ratio $r = 10$:

$S = 10 \times 10 = 100\ \text{mm of snow}$

Example 2 — slightly fluffier snow. With $R = 5\ \text{mm}$ of rain and a ratio $r = 12$:

$S = 5 \times 12 = 60\ \text{mm of snow}$

Ratio reference

Notes and practical uses

• The snow-to-rain ratio depends strongly on air temperature; colder air generally produces fluffier, higher-ratio snow.
• Weather services often report snowfall alongside a “liquid equivalent” — this calculator moves between the two.
• The atmospheric conditions that shape the ratio are closely tied to humidity and temperature; the wet-bulb temperature calculator estimates a related quantity, and the Beaufort scale calculator describes accompanying winds.

FAQ

What ratio should I use? When in doubt, 10:1 is the standard average. Use a higher ratio for cold, dry snow and a lower one for wet snow near the freezing point.

Does 1 inch of rain really equal about 10 inches of snow? On average, yes, but the true figure can range from roughly 5 to over 20 inches of snow per inch of rain depending on conditions.

Can I go from snow back to rain? Yes — divide the snow depth by the ratio to recover the liquid-water (rain) equivalent.