Free rain to snow calculator
Enter the liquid precipitation and the surface temperature to get the snow depth in inches and centimeters — the snow-to-liquid ratio is picked from the temperature using the NWS table, updated live, as you type.
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An estimate for fresh snow — wind and compaction shift the real depth. How accurate is this?
Results are estimates. Consult a professional.
What the snow-to-liquid ratio is
The rain-to-snow calculator turns a liquid precipitation amount — the meltwater a storm drops, the number a rain gauge or forecast gives — into a snow depth. The bridge between the two is the snow-to-liquid ratio (SLR): how many inches of snow you get from one inch of melted water. A 10:1 ratio means one inch of liquid falls as ten inches of snow.
The familiar "ten inches of snow per inch of rain" rule of thumb is only a rough average. Real ratios swing from about 5:1 for heavy, wet, near-freezing snow to 30:1, 40:1, or higher for the dry, feathery powder that falls in deep cold. Because the same meltwater can produce very different depths, the temperature matters as much as the precipitation amount — which is why this tool picks the ratio from the surface temperature for you.
How the rain to snow calculator works
Snow depth is the liquid precipitation multiplied by the snow-to-liquid ratio. The calculator takes the meltwater amount and the surface temperature, looks up the ratio for that temperature from the National Weather Service conversion table, and returns the snow depth in both inches and centimeters along with the ratio it used.
Why temperature sets the snow-to-liquid ratio
Snow depth is mostly about how much air is trapped between the crystals, and that is set by their shape — which is set by the temperature the snow forms and falls through. Two inputs drive the result, and the temperature does the heavy lifting.
Liquid precipitation
This is the meltwater equivalent — what the snow would measure if you melted it down to water. It scales the result directly: double the precipitation and you double the snow depth at the same ratio. It is the number a rain gauge, a snow-water-equivalent reading, or a quantitative precipitation forecast gives you.
Surface temperature
This is the lever that sets the ratio. Near freezing, around 30 °F, snow crystals are simple and partly melted, so they pack densely at roughly 10:1. As the air gets colder, the crystals grow into intricate, branching dendrites that interlock and trap far more air — pushing the ratio to 15:1, 20:1, 30:1, and beyond. The dry, "champagne powder" prized by skiers forms in this deep cold.
Why cold powder piles deeper than wet snow
It is the same water either way — the difference is entirely how much air rides along with it. Wet snow that falls near freezing is dense and heavy: the crystals are blunt, partly melted, and pack tight, so an inch of meltwater barely makes ten inches of snow. Very cold snow is the opposite: delicate, feathery crystals stack loosely with huge air gaps between them, so the same inch of meltwater can pile up thirty or forty inches deep.
A worked example using the rain to snow calculator
A winter storm is forecast to drop 0.5 inches of liquid precipitation while the surface temperature holds around 25 °F. The forecast gives the meltwater, but you want to know how deep the snow will actually pile.
Step 1 — Find the snow-to-liquid ratio
A surface temperature of 25 °F falls in the National Weather Service 27–20 °F band, which carries a snow-to-liquid ratio of 15:1. The calculator selects this automatically from the temperature.
Step 2 — Multiply by the precipitation
Snow depth is the liquid precipitation times the ratio: 0.5 in × 15 = 7.5 in. In metric that is 7.5 × 2.54 ≈ 19.1 cm.
Step 3 — Read the result
The half inch of meltwater becomes about 7.5 inches (19.1 cm) of snow. Had the same storm fallen at 30 °F, the ratio would have been 10:1 and the depth only 5 inches — half again less snow from identical precipitation, purely because of the warmer air.
Snow-to-liquid ratio by temperature
This is the temperature-to-ratio table the calculator uses, from the National Weather Service. Find your surface temperature, read across to the ratio, and multiply your liquid precipitation by it. The last column shows the snow depth from 0.5 inches of meltwater, so you can see how steeply depth climbs as the air gets colder.
| Surface temperature | Snow-to-liquid ratio | Snow type | Depth from 0.5 in liquid |
|---|---|---|---|
| 34–28 °F | 10:1 | Wet, dense snow | 5.0 in |
| 27–20 °F | 15:1 | Settled snow | 7.5 in |
| 19–15 °F | 20:1 | Light, dry snow | 10.0 in |
| 14–10 °F | 30:1 | Fluffy powder | 15.0 in |
| 9–0 °F | 40:1 | Dry powder | 20.0 in |
| −1 to −20 °F | 50:1 | Very cold powder | 25.0 in |
| −21 to −40 °F | 100:1 | Extreme cold powder | 50.0 in |
Snow-to-liquid ratios from the NWS "New Snowfall to Estimated Meltwater Conversion Table" (Observing Handbook No. 7, Figure 11-8). Ratios apply to newly fallen snow only and do not account for wind packing, compaction, or melting. Above ~34 °F precipitation usually falls as rain.
These temperature bands and ratios are the NWS "New Snowfall to Estimated Meltwater Conversion Table" (Observing Handbook No. 7, Figure 11-8), reproduced in NOAA NCEI's "Estimating the Water Equivalent of Snow." At 25 °F, the table's 27–20 °F column gives 0.50 in of meltwater → 7.5 in of snow, matching the worked example above.How to use the rain to snow calculator
- Enter the liquid precipitation. Use the meltwater (rain-equivalent) amount in inches — from a rain gauge, a snow-water-equivalent reading, or a forecast's quantitative precipitation.
- Set the surface temperature. In "From temperature" mode, enter the air temperature in °F and the calculator picks the snow-to-liquid ratio from the NWS table automatically.
- Or enter your own ratio. Switch to "Custom ratio" mode to type a known local or observed value — for example 12:1 for a regional average, or 20:1 for known dry powder.
- Read the snow depth. The hero shows the depth in inches with the centimeter equivalent beside it, plus the ratio that was used.
- Compare scenarios. Hold the precipitation steady and slide the temperature colder to watch the snow depth climb — the clearest way to see how much the ratio matters.
Once you know the depth, the snow load calculator turns it into the weight on a roof, and the wind chill calculator tells you how cold that snowy air will actually feel.
How accurate is the rain to snow conversion?
This is a fast estimate, not a measurement. The snow-to-liquid ratio depends on far more than surface temperature alone — the temperature profile of the whole atmosphere the snow falls through, the crystal types that form, and humidity all shift it. Two storms at the same surface temperature can produce noticeably different ratios, which is why forecasters treat the table as a guide and adjust it.
The table also applies to freshly fallen snow only. Once snow is on the ground it compacts under its own weight, packs down further in wind, and can melt or refreeze — all of which reduce the depth below what the conversion predicts. Strong wind during the storm can also blow light powder into drifts, so the measured depth varies wildly from place to place. Treat the result as the order-of-magnitude depth for new snow, and rely on your local weather service for an actual forecast.
Frequently asked questions about the free rain to snow calculator
About this Rain to Snow calculator
This calculator runs entirely in your browser. Nothing you enter is sent anywhere — the snow depth and snow-to-liquid ratio are computed locally as you adjust the precipitation and temperature, using the National Weather Service conversion table.
It is one of our weather calculators. Browse the full set of free calculators for more snow, climate, and everyday tools.