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Snow Load Calculator

Work out the snow load on your roof in kg/m², total kilograms, and kPa.

How it is calculated

The tool treats the snow as a layer of uniform density. load = depth ÷ 100 × density gives the weight per square metre in kg/m², total = load × area gives the weight in kg, and pressure = load × 9.81 ÷ 1000 gives kPa. Inputs are depth in centimetres, density in kg/m³ (fresh powder is far lighter than wet or compacted snow) and roof area in square metres. Depth, density and area must all be above zero or there is no result. The tool uses a single flat figure: it does not apply roof-pitch reduction, drifting, ice or the legal design snow loads of any country, which differ by region and building code.

Worked example

A roof of 60 m² carries 40 cm of snow with a density of 200 kg/m³. Convert the depth: 40 ÷ 100 = 0.4 m. Load per square metre: 0.4 × 200 = 80.0 kg/m². Total weight: 80 × 60 = 4,800 kg. Pressure: 80 × 9.81 ÷ 1000 = 0.78 kPa. If the same depth were wet snow at 400 kg/m³, every figure would double.

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Common mistakes

  • Entering depth in metres or millimetres. The field expects centimetres, so 0.4 instead of 40 gives a hundred times too little.
  • Using water density (1000 kg/m³) for snow. Fresh snow is much lighter, and so the load would be overstated.
  • Using the same density after rain. Rain-soaked snow can weigh far more than the dry figure.
  • Entering the roof's footprint in square feet. The area must be in square metres.
  • Treating the result as a design value. It is a rough estimate that ignores slope, drifts and the building code, so use it only to judge when to clear snow.

About this calculator

This calculator finds the snow load on a roof from snow depth, snow density, and roof area, converting them into load per square meter (kg/m²), total weight on the structure (kg), and pressure in kilopascals (kPa) — density varies enormously between fresh powder and wet, compacted snow.

Structural engineers and building inspectors use snow load figures to check a roof against its design capacity, and homeowners in heavy-snowfall regions use a rough estimate to judge whether accumulated snow needs to be cleared before it stresses the structure.

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Comments (1)

  • Editorial team

    Snow depth alone says little, because the same 40 cm can weigh several times more once it is wet or packed, so a measured or well-estimated density matters more than the depth. The figure is a flat, uniform layer; drifting, sliding, and rain soaking into the snow can make some parts of a roof carry much more. For any structural decision, ask a qualified engineer. How do you usually estimate the snow's density?

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