How heavy is snow?
Snow can be surprisingly heavy, and its weight depends far more on its density than on its depth. Fresh powder is mostly air, while old or wet snow can weigh as much as a quarter to half its volume in water:
| Type of snow | Density (kg/m³) | Weight per cubic foot |
|---|---|---|
| Fresh, powdery | about 100 | about 6 lb |
| Fresh, wet | about 200 | about 12 lb |
| Settled | about 300 | about 19 lb |
| Old, wet or compacted | about 500 | about 31 lb |
| Ice | about 900 | about 56 lb |
The calculation
load (kg/m²) = depth (m) × density (kg/m³)
The calculator converts the result to pounds per square foot (psf), multiplies by the roof’s horizontal footprint to get the total weight, and shows the water equivalent: 1 kg/m² of snow equals 1 mm of water.
Worked example
12 inches of settled snow on a roof with a 1,500 sq ft footprint:
| Result | Value |
|---|---|
| Snow load | 18.7 psf |
| In kilonewtons per square meter | 0.90 kN/m² |
| Total weight on the roof | about 28,100 lb (14 tons) |
| Water equivalent | 3.6 in |
The same foot of snow, once soaked by rain, could weigh over 31 psf.
How much can a roof hold?
Roofs are designed for a design snow load set by the local building code, which is based on a ground snow load map (ASCE 7 in the United States) and adjusted for roof slope, exposure and heating. Values are often around 20 to 30 psf in moderate climates and can exceed 100 psf in mountain regions. Older buildings, flat roofs and roofs where snow drifts against a wall or a higher roof are most at risk.
Warning signs
- Sagging roof lines or ceilings.
- New cracks in drywall or plaster.
- Doors and windows that start to stick.
- Creaking, cracking or popping sounds.
If you notice these, leave the building and call a professional.
Tips
- Measure depth in several places: drifts near walls, valleys and lower roofs can be two or three times deeper.
- Rain on snow adds weight quickly, because the snow absorbs the water.
- Use a roof rake from the ground rather than climbing onto a snowy roof, and remove snow evenly.