Snow Load Calculator
Free online snow load calculator — estimate the weight of snow on your roof using roof dimensions, pitch, snow thickness, and snow type. Get snow load in psf, total weight, and roof area instantly.
About This Calculator
The Snow Load Calculator helps homeowners, builders, and structural engineers estimate the weight of snow on a roof. Whether you are assessing whether to shovel snow after a heavy blizzard or designing a new roof to meet building code requirements, this calculator provides quick and accurate snow load estimates based on roof geometry and snow conditions.
The snow load is calculated using the standard engineering formula: Snow Load (psf) = Snow Thickness (ft) × Snow Density (lb/ft³). The roof pitch factor accounts for the increased surface area of sloped roofs. The pitch factor is computed as √(144 + pitch²) / 12, where the pitch is the rise in inches per 12 inches of horizontal run. The total roof surface area equals the footprint area (length × width) multiplied by the pitch factor. The total snow weight is then the roof area multiplied by the snow load per square foot.
Snow density varies significantly with snow type — fresh snow is light and fluffy at about 3.75 lb/ft³, while ice is 57.25 lb/ft³, over 15 times heavier. This calculator includes six snow types: fresh snow, damp fresh snow, settled snow, wind-packed snow, very wet snow, and ice. Always use the denser type if unsure to err on the side of safety.
Regional Notes
United States: The ASCE 7 standard specifies ground snow loads for all US locations. Most residential roofs are designed for 20–40 psf ground snow loads. Buildings in heavy-snow states like New York, Michigan, and Colorado may have higher design requirements. Roof snow load is typically 60–80% of the ground snow load.
Canada: The National Building Code of Canada (NBC) provides 1-in-50-year ground snow load values for all provinces and territories. Roof snow loads are adjusted for exposure, roof slipperiness, and importance. Quebec and British Columbia have some of the highest snow load requirements in Canada.
United Kingdom: BS EN 1991-1-3 (Eurocode) governs snow load design in the UK. Ground snow loads vary by altitude and location, ranging from about 0.3 kN/m² in southern England to over 1.5 kN/m² in the Scottish Highlands. Roof snow loads account for roof shape, drift, and altitude coefficients.
Frequently Asked Questions
What is snow load?
Snow load is the downward force exerted by accumulated snow on a structure, typically measured in pounds per square foot (psf). It depends on the snow depth, density, and roof geometry. Building codes like ASCE 7 specify minimum design snow loads to ensure roofs can safely support the expected snow accumulation in a given region.
How do you calculate snow load on a roof?
Snow load is calculated as snow thickness (in feet) multiplied by snow density (lb/ft³). The total snow weight on a roof equals the roof surface area multiplied by the snow load. Roof pitch increases the surface area — the pitch factor is the square root of (144 + pitch²) divided by 12. For example, a 40 ft × 30 ft roof with 6/12 pitch and 12 inches of fresh snow has a snow load of about 3.75 psf and a total weight of roughly 5,000 lbs.
What are the different snow types and their densities?
Snow density varies significantly by type: fresh snow is about 3.75 lb/ft³, damp fresh snow is 6.87 lb/ft³, settled snow is 15.61 lb/ft³, wind-packed snow is 23.41 lb/ft³, very wet snow is 46.82 lb/ft³, and ice is 57.25 lb/ft³. Ice is over 15 times denser than fresh snow, making it particularly hazardous for roof structures.
When should I remove snow from my roof?
You should remove snow from your roof when the snow load approaches or exceeds your roof's design capacity. Warning signs include sagging ceiling tiles, creaking or popping noises, cracking walls, and ice dam formation. Most residential roofs in the US are designed for ground snow loads of 20–40 psf. If you observe any structural distress, contact a structural engineer immediately.
How does roof pitch affect snow load?
Steeper roofs shed snow more effectively, reducing the accumulated snow depth. However, a steeper pitch also increases the total roof surface area, which can increase the total snow weight for a given snow depth. The pitch factor is calculated as √(144 + pitch²) / 12, where pitch is the rise in inches per 12 inches of run. A higher pitch results in a larger pitch factor and greater roof area.
What is the ASCE 7 standard for snow loads?
ASCE 7 is the American standard for Minimum Design Loads for Buildings and Other Structures. It specifies ground snow load values for every US region, which are then adjusted for roof exposure, thermal factors, and importance to determine the design snow load. Buildings constructed before 1988 may not comply with current ASCE 7 standards and could be at higher risk during heavy snowfall.
What is the difference between ground snow load and roof snow load?
Ground snow load is the weight of snow on the ground at a given location, used as the base value in building codes. Roof snow load is typically lower than ground snow load because wind, roof slope, and heat loss from the building cause some snow to slide off or melt. The roof snow load is calculated by multiplying the ground snow load by factors for exposure, thermal conditions, and roof slope.
How does snow load affect home insurance in the US, Canada, and the UK?
In the US, most homeowner insurance policies cover snow collapse damage, but some may require a separate rider in heavy-snow regions. In Canada, insurance typically covers sudden snow collapse but may exclude gradual damage from ice dams. In the UK, standard buildings insurance covers damage from snow and ice, though policies may have exclusions for lack of maintenance. Check with your insurer about snow load coverage limits.