Convert rainfall amounts to equivalent snowfall depth. Adjusts for temperature, snow density, and moisture content with detailed accumulation estimates.
The classic "10-to-1" rule—one inch of rain equals ten inches of snow—is a convenient approximation, but real snow-to-rain ratios vary dramatically with temperature and moisture content. At 28°F, the ratio might be 15:1 (fluffy snow), while near freezing at 34°F, heavy wet snow might accumulate at only 5:1.
This rain-to-snow calculator goes beyond the simple rule, adjusting the conversion ratio based on temperature, humidity, and snow type. It calculates the snow water equivalent (SWE), which is the standard meteorological measurement of how much liquid water is contained in a given depth of snow. SWE is critical for water resource management, flood forecasting, and agricultural planning.
The tool also estimates snow density, compaction over time, snow load on structures, and the range of possible accumulation given weather uncertainty. Whether you're a homeowner estimating how much shoveling awaits, a ski resort tracking base depth, a structural engineer calculating roof loads, or a water manager estimating spring runoff, this calculator provides practical answers from simple weather data.
Understanding the rain-to-snow relationship is essential in regions where both precipitation types occur. A forecast of "0.5 inches of liquid equivalent" can mean 3 inches of heavy slush or 10 inches of powder—the difference matters enormously for transportation, infrastructure, and daily life.
Use this calculator when a forecast gives liquid-equivalent precipitation and you need a rough snowfall depth estimate that accounts for snow type instead of assuming a flat 10:1 ratio. It is useful for travel prep, snow removal planning, roof-load checks, and comparing colder versus wetter storm scenarios. It also helps explain why the same liquid forecast can turn into very different snow totals.
Snow depth = rain_inches × snow_ratio. SWE = snow_depth / snow_ratio (or simply = rain amount). Snow density = 1000 / snow_ratio (kg/m³). Roof load (psf) = SWE_inches × 5.2. Snow ratios by temp: 34°F → 5:1, 30°F → 10:1, 25°F → 15:1, 20°F → 20:1, 15°F → 30:1, 0°F → 40:1.
Result: 15 inches of snow
At 25°F, the snow ratio is approximately 15:1. One inch of rain equivalent produces about 15 inches of fluffy snow with a density of about 67 kg/m³.
**Above 32°F (0°C):** Rain or freezing rain, ratio 1:1 to 3:1. **30–32°F:** Heavy wet snow, 5–8:1. **25–29°F:** Standard snow, 10–15:1. **20–24°F:** Dry fluffy snow, 15–20:1. **10–19°F:** Very light powder, 20–30:1. **Below 10°F:** Ultra-light powder, 30–50:1. **Below −20°F:** Diamond dust, 40–50:1.
These ratios assume calm wind conditions. Add wind and the snow compacts, reducing the ratio by 30–50%. Lake-effect and ocean-effect snow is typically wetter regardless of temperature.
Fresh snow loads on flat roofs range from 1 psf (light powder) to 12+ psf per foot of depth (wet snow). Most residential roofs in snow country are designed for 20–40 psf ground snow load with appropriate reduction factors. Accumulated compacted snow and ice can exceed design loads, especially in historic snowfall events. Clear roofs when accumulation approaches local code limits.
In the western United States, mountain snowpack provides 50–75% of annual water supply through spring and summer melt. USDA SNOTEL stations measure SWE across the mountains. A below-average snowpack year means drought risk, while above-average brings flood risk. Understanding SWE helps communities plan water allocation months in advance.
The standard approximation is 10:1 (10 inches of snow per 1 inch of rain). However, actual ratios range from 3:1 (heavy sleet) to 50:1 (extreme cold powder) depending on temperature and moisture.
SWE is the depth of water that would result from melting a given depth of snow. It equals the original liquid precipitation amount. A 10-inch snowpack with 10:1 ratio has 1 inch of SWE.
Colder temperatures produce smaller, drier ice crystals with more air space between them. Warmer temperatures near freezing produce larger, wetter flakes that pack together densely.
Fresh fluffy snow (30:1): ~2 lbs/ft³. Average snow (10:1): ~6.2 lbs/ft³. Wet heavy snow (5:1): ~12.5 lbs/ft³. Packed/old snow: 15–25 lbs/ft³. Ice: 57.2 lbs/ft³.
Multiply total SWE (inches) by 5.2 to get pounds per square foot. Most roofs are designed for 20–40 psf snow load, but consult local building codes.
Yes. Wind breaks snow crystals into smaller fragments, increasing density. Windblown snow can be 2–3× denser than sheltered snow at the same temperature.