Snow Load Calculator
Weigh the snow sitting on a roof. Enter depth in inches, pick the snow type from fresh powder to ice, and optionally add roof area in square feet to get pounds per square foot, total load, and a read on typical design capacity.
Example: with Snow depth (in) 18 · Snow type (density) Settled snow (~12 lb/cu ft) · Roof footprint (sq ft) 1500 → Snow load: 18.0 psf (88 kg/m2).
- Total weight on roof27,000 lb (13.5 tons) on 1,500 sq ft
- How that comparesBelow 20 psf, the common minimum design roof snow load in the US — typically fine, but verify your local ground snow load
Computed by the calculator below using its default values. Change any input to see your own numbers.
Load (psf) = depth (ft) × snow density. Density is everything: 18 in of powder is under 8 psf, but 18 in of wet spring snow is nearly 40.
Depth means little without density
Snow load is depth times density, and density varies tenfold. Fresh powder runs 3–7 lb per cubic foot, settled snow 10–15, wind-packed drifts around 20, saturated spring snow 20–26, and solid ice 57 — figures consistent with USACE and National Weather Service snow-density ranges. So a dramatic 3 ft of powder (about 15 psf) can stress a roof less than 8 in of ice (38 psf). Rain on snow is the classic emergency: the snowpack absorbs the rain and gains weight within hours without gaining depth.
For design, engineers do not use storm-by-storm density. ASCE 7 starts from a mapped ground snow load and applies exposure, thermal, slope, and importance factors, plus drift surcharges where roofs step. This calculator answers the operational question — what is up there right now — not the design question.
How it’s calculated
Snow load (psf) = depth (in) ÷ 12 × density (lb/cu ft), using typical published densities: fresh powder 5, settled 12, wind-packed 20, wet spring snow 25, ice 57 (USACE/NWS snow-density ranges). Total = psf × roof footprint. Metric shown at 1 psf = 4.88 kg/m2. Comparison bands reference the common 20 psf US minimum design roof snow load.
Assumes uniform depth of one snow type — real roofs hold layered snowpack and drifts that concentrate load; structural adequacy is a question for your local ground snow load, ASCE 7 factors, and an engineer.
Weight of 12 inches of snow by type
| Snow type | Density | Load per sq ft |
|---|---|---|
| Fresh light powder | 5 lb/cu ft | 5 psf |
| Settled snow | 12 lb/cu ft | 12 psf |
| Wind-packed | 20 lb/cu ft | 20 psf |
| Wet spring snow | 25 lb/cu ft | 25 psf |
| Solid ice | 57 lb/cu ft | 57 psf (4.8 psf per inch) |
Depth × density; densities from typical USACE/NWS published snow-density ranges.
Common mistakes
- Judging load by depth alone — wet snow weighs 4–5× powder, and ice more than 10×.
- Ignoring rain-on-snow: the pack soaks it up and can add 5+ psf in a storm with no new depth.
- Averaging away drifts; a stepped roof or leeward slope can carry 2–3× the field load in one spot.
- Climbing onto a loaded roof to shovel it — use a roof rake from the ground; falls hurt more people than collapses.
Frequently asked questions
How do you calculate snow load?
Multiply depth in feet by snow density: load (psf) = depth (in) ÷ 12 × density (lb/cu ft). 18 inches of settled snow at 12 lb/cu ft is 1.5 × 12 = 18 psf.
How much snow can a typical roof hold?
Many US roofs are designed for at least a 20 psf snow load, and snow-country roofs commonly 30–60 psf or more. That is roughly 3–4 ft of settled snow for a 40 psf roof — but the honest answer depends on your local code and the structure's condition.
How much does one foot of snow weigh?
On each square foot: about 5 lb if it is light powder, 12 lb settled, 20 wind-packed, and 25 for wet spring snow. A foot of solid ice would be 57 lb.
When should I worry and call someone?
Warning signs include new interior door sticking, cracking sounds, sagging ridge lines, or visible bowing. Clear what you can safely reach with a roof rake from the ground, and have a structural engineer assess any roof showing distress — this tool is an estimate, not an inspection.
Does roof pitch change the load?
Yes — steep, slippery roofs shed snow, and design codes reduce loads above about 30° slopes. Flat and low-slope roofs hold everything and collect drifts, which is why they fail more often.