Snow Water Equivalent Calculator
Calculate the water content of snow (SWE).
Find how many millimeters or inches of water are stored in a given snow depth based on snow density.
Snow Water Equivalent (SWE) is the amount of liquid water contained in a snowpack. It is one of the most important measurements in hydrology, water resource management, flood forecasting, and skiing/avalanche risk assessment.
The formula: SWE = Snow Depth × Snow Density / Water Density
Since water density = 1 g/cm³ (or 1000 kg/m³): SWE (mm) = Snow Depth (cm) × (Snow Density kg/m³) / 1000 × 10
Or more simply: SWE (mm) = Snow Depth (cm) × Snow Density Ratio × 10
Snow density by type:
| Snow Type | Density (kg/m³) | Density Ratio |
|---|---|---|
| Fresh fluffy snow | 50–100 | 5–10% |
| Typical new snow | 100–150 | 10–15% |
| Settled snow (1–2 days old) | 200–300 | 20–30% |
| Wind-packed snow | 350–400 | 35–40% |
| Wet/spring snow | 400–550 | 40–55% |
| Old/compacted snowpack | 500–600 | 50–60% |
| Ice (maximum) | 900 | 90% |
The “10:1 rule of thumb”: Fresh snow is often assumed to be 10:1 — 10 inches of snow equals 1 inch of water equivalent. This is a rough average; actual ratios range from 4:1 (very wet snow) to 30:1 (very dry powder).
Why SWE matters:
- Water supply: Mountain snowpack is a major freshwater reservoir. Spring snowmelt fills rivers and reservoirs.
- Flood risk: Rapid SWE melt (from warm rain on snowpack) causes devastating floods.
- Ski resorts: SWE determines how long a ski season lasts and slope conditions.
- Agriculture: Farmers track SWE to predict irrigation water availability.
Real-world example: A 50 cm snowpack with density 200 kg/m³: SWE = 50 × 200 / 1000 × 10 = 100 mm of water That is 100 liters per square meter stored in the snowpack.