Last updated: 2026-06-21

Roof Snow Load

A roof snow load calculator estimates how heavily snow presses on a roof. Enter the depth of snow, its type — from fresh powder to packed ice — and the roof area, and it returns the load per unit area, the total weight of snow on the roof, and a rough sense of whether that load is light or worth acting on. It helps homeowners decide when to clear a roof and lets you compare the actual load against the design figure for your region.

How snow load is calculated

A layer of snow of depth $h$ and density $\rho$ has a mass of $\rho h$ per square metre. Multiplying by gravity gives the pressure on the roof, and multiplying the mass by the roof area gives the total weight:

where $p$ is the load per area, $g$ is gravitational acceleration, $W$ is the total weight, and $A$ is the roof area. Density does the heavy lifting here: the same depth of wet snow can weigh five times as much as fresh powder, so the type of snow matters as much as how deep it is.

Worked example

Half a metre of settled snow, at about 250 kg/m³, on a 100 m² roof:

That is about 12.5 tonnes resting on the roof, at a load near 1.2 kilopascals. Many building codes set regional design snow loads in the range of 1 to 3 kilopascals, so this load is moderate for a snowy area — but a roof already weakened, very shallow, or carrying drifted snow has less margin.

Reading the result

The load figure is most useful next to the design snow load that your local building code specifies for your area, which is what the roof was meant to carry. Snow rarely sits evenly: wind drifts it against walls and into valleys, and rain or a thaw can soak and pack it so the load climbs without the depth changing. Treat this as an estimate of the current load, clear roofs safely from the ground where you can, and consult a structural engineer about any roof you are worried about. For the slope that helps snow shed, see Roof Pitch Calculator.