Snow Load Calculator — Roof Snow Weight & Design Pressure (ASCE 7)
Calculate how many pounds of snow your roof is carrying. Enter snow depth, snow type (fresh to wet), roof area, and slope to get the design snow pressure in psf and total load in pounds — based on the ASCE 7 simplified method.
inches
Snow type / density
ft²
°
Total weight of snow on the roof (plan area × design snow pressure)
8.1 psf
design load- 1
Ground snow load
(12 ÷ 12) × 15 pcf = 15Snow depth converted to feet, then multiplied by density to get pounds per square foot. - 2
Flat-roof snow load
0.7 × 1 (Ce) × 15 psf = 10.5 - 3
Slope factor Cs
1 − (20° − 5) ÷ 65 = 0.769 - 4
Design roof snow load
0.769 × 10.5 psf = 8.08 - 5
Total roof snow load
8.08 psf × 1,200 ft² = 9,692
How does this calculator work?
Ground load p_g = (depth_in/12) × density_pcf; design roof load p_s = 0.7 × Ce × Cs × p_g; total weight = p_s × plan_area (ft²). Settled 12-inch snow on a 1,200 ft² roof at 20° slope yields roughly 10,000–12,000 lbs. Use a licensed structural engineer for permit-level calculations — this is a quick awareness tool based on ASCE 7-22 (2024 IBC).
Formula
How this is calculated
Snow exerts a vertical downward force on a roof equal to its weight per unit area (called snow pressure, measured in pounds per square foot, psf). The ground snow load p_g is calculated from the on-ground snow depth and density: weight = depth (converted to feet) × density (pcf). Density varies enormously — fresh powder weighs about 5 pcf while wet, compacted snow can reach 40 pcf.
The ASCE 7-22 standard (the structural design code used across the United States) converts ground snow to a design flat-roof snow load using p_f = 0.7 × Ce × Ct × Is × p_g. The 0.7 factor accounts for wind-driven redistribution that reduces roof accumulation relative to the ground; Ce is the exposure factor (windy ridges have Ce ≈ 0.7, sheltered valleys Ce ≈ 1.2); Ct is the thermal factor (a warm, heated building melts snow faster; this calculator defaults Ct = 1.0 for a heated building); Is is an importance factor (1.0 for ordinary buildings). For sloped warm roofs, the slope factor Cs ramps from 1.0 at 5° down to 0 at 70°, reflecting that steep pitches shed snow. The total load on the structure is the design pressure multiplied by the horizontal (plan) area of the roof — not the sloped surface.
This calculator implements the ASCE 7 simplified method for quick structural awareness checks. For official building permit or structural engineering purposes, a licensed structural engineer must perform a full site-specific analysis that includes drift loads, unbalanced loads, and local jurisdiction adjustments. All default constants reflect ASCE 7-22 and 2024 IBC values.
Frequently asked questions
Most residential roofs in North America are designed for ground snow loads of 20–40 psf, depending on climate zone. The design roof load is roughly 14–28 psf (after the 0.7 factor and slope reduction). A 12-inch depth of settled snow (~15 pcf) produces about 15 psf on the ground — close to the design limit in moderate snow regions, and why roof clearing is recommended after heavy storms.
Ce ranges from 0.7 (fully exposed ridge, heavy wind removes snow) to 1.2 (heavily sheltered by trees or adjacent buildings). A typical suburban or rural roof uses Ce = 1.0. ASCE 7-22 Table 7.3-1 provides the full classification: fully exposed → 0.7, partially exposed → 1.0, sheltered → 1.2.
Use the horizontal (plan) area — the footprint of the roof as seen from directly above. ASCE 7 snow loads are defined as forces per unit of horizontal area because snow falls vertically. Multiplying by sloped surface area would overestimate the load.
Also known as
TG we-Calculate Editorial Team. (2026). Snow Load Calculator — Roof Snow Weight & Design Pressure (ASCE 7) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/snow-load-calculator
TG we-Calculate Editorial Team. "Snow Load Calculator — Roof Snow Weight & Design Pressure (ASCE 7)." TG we-Calculate. 2026. https://we-calculate.com/calculator/snow-load-calculator.
TG we-Calculate Editorial Team, "Snow Load Calculator — Roof Snow Weight & Design Pressure (ASCE 7)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/snow-load-calculator
@misc{wecalculate_snow_load_calculator, title = {Snow Load Calculator — Roof Snow Weight & Design Pressure (ASCE 7)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/snow-load-calculator}}, year = {2026}, note = {TG we-Calculate} }
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