Snow Water Equivalent (SWE) Calculator
Calculate snow water equivalent from snow depth and density.
Find how much liquid water is stored in a snowpack.
Results in mm, inches, liters, and gallons.
Snow Water Equivalent (SWE) The depth of liquid water that would result if all the snow melted.
SWE (mm) = Snow Depth (m) × Snow Density (kg/m³) / Water Density (1000 kg/m³) × 1000
Or more simply: SWE (mm) = Depth (cm) × (Snow Density / Water Density)
Snow Density by Type
- New light snow: ~50 kg/m³ (very fluffy, lots of air)
- Average fresh snow: ~150 kg/m³
- Settled snow (a few days old): ~250 kg/m³
- Wind-packed snow: ~350 kg/m³
- Firn / old compacted snow: ~500 kg/m³
- Pure ice: 917 kg/m³
The 10:1 Rule of Thumb “10 inches of snow equals 1 inch of water” — this assumes average snow density (~100 kg/m³). In reality, the ratio ranges from:
- 3:1 (wet, heavy coastal snow)
- 10:1 (typical)
- 30:1 (very dry powder in cold, continental climates)
Why SWE Matters SWE is the key variable for water resource management, flood forecasting, and ski resort snowpack reports. Mountain snowpack stores roughly 30% of all fresh water in the western USA.