🌨️ Snow Load Calculator (Roof)
Enter the snow depth and choose (or set) the snow density to estimate the roof load in lb/ft², kPa and kg/m².
Roof load
18.43 lb/ft²
In kPa
0.8826
Mass per area
90 kg/m²
Snow load on a flat roof is the snow depth times its density: mass per area = depth × density, and the pressure is that times gravity. Snow density varies hugely, fresh light snow around 50-100 kg/m³, settled 200-300, wet or packed 400-500, and ice near 900, so depth alone can\'t tell you the load. For structural decisions, use your local building code\'s design snow load (e.g. ASCE 7), which also accounts for drifting and roof shape. 🔒 In your browser.
How the snow load calculator (roof) works
The load a roof carries is the mass of snow per unit area, depth × snow density, expressed as a pressure. The tool multiplies depth by density to get kilograms per square metre, then converts to a pressure in kilopascals (× gravity) and to pounds per square foot. Because snow density ranges enormously, light fresh snow near 50-100 kg/m³ up to wet or packed snow at 400-500 and ice near 900, depth alone can't tell you the weight.
This is a quick estimate, not a structural determination. Real roofs are designed to a code "design snow load" (such as ASCE 7 in the US) that accounts for the ground snow load, roof slope and exposure, thermal effects, and drifting, which can pile far more snow on one part of a roof. If you're worried about a roof, consult the code or an engineer; clear snow safely.
Frequently asked questions
How much does snow weigh on a roof?
It depends on depth and density. Fresh light snow is roughly 5-10 lb/ft² per foot of depth; wet or packed snow much more. The tool computes the load from the depth and a density you set, e.g. 30 cm of settled snow (300 kg/m³) is about 18 lb/ft².
How do you calculate snow load?
Load = snow depth × snow density. In metric that gives kg/m² (mass per area); multiply by gravity for kPa, and convert for lb/ft². The big unknown is density, which the tool provides presets for.
What is the density of snow?
Very variable: fresh light snow around 50-100 kg/m³, settled snow 200-300, wet or packed snow 400-500, and solid ice near 900 kg/m³. That's why two roofs with the same snow depth can carry very different loads.
When is snow load dangerous for a roof?
When it approaches the roof's design capacity, which varies by region and building. Wet, heavy or rain-soaked snow and drifting are the biggest risks. If you notice sagging, cracking or sticking doors, treat it seriously and clear snow safely or call a professional.
Is this the same as the code design snow load?
No, building codes (e.g. ASCE 7) set a design snow load using the local ground snow load with factors for roof slope, exposure, thermal condition and drifting. This tool estimates the load from actual measured depth and density; use the code for structural design.