Snow Load Calculator
The load snow puts on a roof — from depth and snow type — with the total weight and how the roof pitch reduces it.
How much the snow on the roof weighs.
How the snow load calculator works
Snow load is depth × density. Density is the variable that matters: fresh powder is around 70 kg/m³, settled snow 200, and wet or compacted snow 400 or more — so the same depth can weigh six times as much depending on its history.
A steep roof sheds snow, and codes apply a slope factor that reduces the design load above about 30°. Ice at 900 kg/m³ is the worst case and does not shed at all.
Formula: load = depth × density × slope factor
Worked examples
| Inputs | Snow load | Note |
|---|---|---|
| 500 mm of settled snow | 0.981 kPa | 0.98 kPa, 10 tonnes on a 100 m² roof |
| The same depth as wet snow | 1.961 kPa | twice the load |
| A steep roof sheds it | 0.49 kPa | the slope factor halves the load |
FAQFrequently asked questions
How much does snow weigh?
Fresh powder about 70 kg/m³, settled snow 200, wet or compacted 400, ice 900. Depth alone tells you very little.
How much is 500 mm of settled snow?
About 100 kg per square meter, or 1 kPa — ten tonnes on a 100 m² roof.
Does a steep roof help?
Yes, above about 30°. Codes apply a slope factor that falls to zero near 70°, on the basis that snow slides off.
What is the design load where I am?
That is a code question and it varies enormously by location and altitude. This calculates the load from an actual depth — it is not a substitute for the ground snow load in your building code.
What about drifting?
Drifts against a wall or in a valley can be several times the flat-roof depth, and they are what usually causes collapse. Codes treat drift loading separately.
Where these figures come from
- The Engineering ToolBox — material densities, coverage and unit data — bulk densities, concrete at 2,400 kg/m³, board and sheet sizes
- Gypsum Association — gypsum board sizes — 4 × 8 and 4 × 12 ft sheets
- ADA Standards for Accessible Design — ramps (§405) — maximum running slope 1:12
- International Code Council — the International Residential Code
Last checked: September 2026. Coverage rates and material sizes are typical manufacturer figures — check the product you buy.