Estimate the weight of snow on your roof in pounds per square foot from the depth and snow type — a planning estimate, not a structural design figure.
psf = (depth_in ÷ 12) × snow_density
Snow load is the depth in feet times the snow's density. Fresh snow is light (about 7 lb/ft³); settled or wet snow is far heavier (15–30 lb/ft³).
Loads above about 20 psf warrant attention on many residential roofs. This is a rough estimate — not a substitute for an engineer.
Twelve inches of settled snow has a density around 15 lb per cubic foot. One foot deep is therefore about 15 lb per square foot. On a 1,500 square foot roof that's 22,500 lb — over 11 tons sitting on the structure.
That 15 psf is comfortably under the ~20 psf many residential roofs are designed for, but wet spring snow or an ice layer can be two to four times heavier. The same depth of ice (around 57 lb per cubic foot) would be 57 psf — well into dangerous territory. This is exactly why this is a planning estimate, not a design tool: real load calculations follow ASCE 7 and your local code, and structural decisions need a licensed engineer.
This is a planning estimate using typical snow densities. Structural design loads follow ASCE 7 and local code — consult a licensed engineer for anything load-bearing.
Settled snow is about 15 lb per cubic foot, so 12″ of it is roughly 15 lb per square foot.