🌨️ 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.