Snow Load Calculator
Free Snow load Calculator for roofing projects. Enter dimensions to get material lists and cost estimates. Includes formulas and worked examples.
Reviewed by Abdullah, Technical Content Specialist
Formula
Snow Load (psf) = (Snow Depth in ft) x Snow Density (pcf) x Slope Factor
Convert snow depth to feet, multiply by the snow density in pounds per cubic foot to get the ground snow load in psf. Apply a slope reduction factor for steep roofs (pitches above 15 degrees). Multiply by the roof footprint area to get the total load in pounds.
Worked Examples
Example 1: Moderate Snow on Ranch Roof
Problem:Calculate snow load for 12 inches of settled snow (15 pcf) on a 40x30 ft roof with 4/12 pitch.
Solution:Ground snow load = (12/12) x 15 = 15.0 psf\nRoof angle = 18.4 degrees (no significant slope reduction)\nRoof snow load = 15.0 psf\nTotal load = 15.0 x 1,200 = 18,000 lbs
Result:15.0 psf, 18,000 lbs total (9.0 tons)
Example 2: Heavy Snow on Steep Roof
Problem:Calculate snow load for 24 inches of packed snow (25 pcf) on a 50x30 ft roof with 10/12 pitch.
Solution:Ground snow load = (24/12) x 25 = 50.0 psf\nRoof angle = 39.8 degrees (slope reduction applies)\nReduction factor = ~85%\nRoof snow load = 50.0 x 0.85 = 42.5 psf\nTotal = 42.5 x 1,500 = 63,750 lbs
Result:42.5 psf, 63,750 lbs total — High risk
Frequently Asked Questions
How do I calculate the snow load on my roof?
Snow load is calculated by multiplying the depth of snow in feet by the density of the snow in pounds per cubic foot. Fresh light snow weighs about 5-10 pcf, settled snow 10-20 pcf, packed snow 20-30 pcf, and ice or ice-laden snow 40-57 pcf. For example, 12 inches of settled snow at 15 pcf creates a load of 1 ft x 15 pcf = 15 psf (pounds per square foot). Multiply by the roof area for total load. Steeper roof pitches reduce the effective snow load because snow slides off more readily.
What snow load can a typical residential roof support?
Most residential roofs are designed for 20-40 psf snow loads depending on geographic location and local building codes. Roofs in northern climates or mountain areas may be designed for 50-80 psf or more. The IRC requires roofs to support the ground snow load specified by ASCE 7 for the location, adjusted for exposure, thermal factor, and importance. If your calculated snow load approaches the design capacity, consider removing snow from the roof to prevent structural damage.
When should I remove snow from my roof?
Consider removing snow when the accumulated load exceeds 20 psf or when you notice warning signs such as doors sticking, cracks appearing in walls or ceilings, sagging ceiling tiles, or unusual creaking sounds. For most roofs, about 4 feet of fresh snow, 2 feet of packed snow, or 1 foot of ice-crusted snow approaches the danger zone. Use a roof rake from the ground when possible and never get on a snow-covered roof. Professional snow removal is recommended for large or steep roofs.
How does roof pitch affect snow load?
Steeper roof pitches reduce snow accumulation because snow slides off more readily. Roofs with pitches above 30 degrees (about 7/12) see significant reduction in snow load. ASCE 7 provides slope reduction factors that decrease the design snow load for steeper roofs. However, this also means snow accumulates at the base of the roof and on lower adjacent roofs, creating drift loads that must be accounted for in structural design. Low-slope roofs retain nearly all the snow that falls on them.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy