Roof Snow Load Calculator
Enter your roof size, the depth of snow on it and whether it is light and dry or wet and heavy. You'll get the load in pounds per square foot and the total weight, and you can compare it with your roof's design snow load.
- FEMA snow weights
- Feet or metric
- Design load check
2 Snow load
Updates as you type| Snow | 12" at 21 lb per sq ft per foot = 21 lb per sq ft |
|---|---|
| If the snow is light and dry | 3 lb per sq ft |
| If the snow is wet and heavy | 21 lb per sq ft |
Snow drifts deeper at valleys, dormers and where a higher roof meets a lower one, so the load is rarely even. Check the depth in several spots, from the ground or a window, and use the deepest.
Quick answer
A foot of fresh snow weighs 3 lb per sq ft when light and dry and 21 lb per sq ft when wet and heavy, according to FEMA. One inch of ice adds a little less than 5 lb per sq ft. A foot of wet snow on a 40 × 30 ft roof weighs about 25,200 lb, or 12.6 tons.
Roof snow load by depth
| Snow depth | Light, dry | Wet, heavy | 1,500 sq ft roof, wet |
|---|---|---|---|
| 6" | 1.5 lb/sq ft | 10.5 lb/sq ft | 15,750 lb |
| 12" | 3 lb/sq ft | 21 lb/sq ft | 31,500 lb |
| 18" | 4.5 lb/sq ft | 31.5 lb/sq ft | 47,250 lb |
| 24" | 6 lb/sq ft | 42 lb/sq ft | 63,000 lb |
| 36" | 9 lb/sq ft | 63 lb/sq ft | 94,500 lb |
| 48" | 12 lb/sq ft | 84 lb/sq ft | 126,000 lb |
Weights from FEMA P-957: 3 lb per sq ft per foot of light, dry fresh snow and 21 lb per foot of wet, heavy snow. Total for a 1,500 sq ft roof footprint. The light figure is for fresh snow only: FEMA notes roof snow can soften in the sun and become denser, so for older snow use the wet, heavy column. Use the calculator above for your exact size.
How much snow weighs
FEMA's Snow Load Safety Guide (P-957) gives these weights:
| Layer | Weight per sq ft |
|---|---|
| 1 ft of light, dry fresh snow | 3 lb |
| 1 ft of wet, heavy snow | 21 lb |
| 1 inch of ice | a little under 5 lb |
| 1 ft of ice | about 57 lb |
The guide notes that snow density varies by region, so a foot of snow in one state need not weigh the same as a foot in another. When you're not sure, use the wet, heavy figure.
Worked example
A 40 × 30 ft roof has a 1,200 sq ft footprint. With 12 inches of wet snow on it, the load is 1 ft × 21 = 21 lb per sq ft. Over the whole roof that's 21 × 1,200 = 25,200 lb. The same depth of light, dry snow would weigh 3 lb per sq ft.
How much can your roof hold?
That depends on its design snow load, which the engineer or builder set from the local building code. FEMA's guide says it can be found on the construction drawings, and that without drawings you should have a licensed design professional work it out. Your building department can tell you the snow load today's code requires where you live. An older roof may have been built for less: FEMA notes that drifting snow loads only entered the building codes in 1975 in the East and Midwest and 1988 in the West.
Don't judge the roof by the snow on the ground. FEMA's guide says assuming ground snow weight is the same as roof snow load is incorrect: roof snow load also depends on wind exposure, roof slope and shape, obstructions and how warm the building is.
Warning signs of too much snow
FEMA lists these signs that a roof is overstressed:
- Sagging ceilings or roof framing
- Popping, cracking and creaking noises
- Doors or windows that can no longer be opened or closed
- Cracked or split wood members, and cracks in walls or masonry
- Severe roof leaks
FEMA's advice if you see any of them: get everyone out of the building promptly and have a qualified design professional, such as a Professional Engineer, inspect it.
Removing snow safely
FEMA notes that most buildings are not at risk of snow-induced failure, and that trying to remove snow from a roof is, more often than not, more hazardous than beneficial. Snow can be removed from the ground, which keeps people off the roof. If it has to come off:
- Keep people away from the area below, where snow and icicles can fall.
- Use a plastic shovel or a non-metal roof rake, not picks or sharp tools, which damage the roofing.
- Leave at least 2 inches of snow on the roof. Scraping it bare can damage the roof covering.
- On sloped roofs, a roof rake can pull snow that slides at any moment, so stay well back from the eave.
- Don't pile removed snow elsewhere on the roof, and keep it away from exits, downspouts and vents.
- Clear drifts first, and don't leave one part of the roof loaded while another is bare. FEMA notes an uneven load is riskier than an even one.
FEMA's guide calls for following OSHA rules for rooftop work, with fall-arrest harnesses where they apply, and highly recommends a licensed, insured roofing contractor who has removed snow before. If there is any concern the roof could collapse, stop and get everyone out.
Frequently asked questions
How much does a foot of snow weigh on a roof?
From 3 lb per sq ft for light, dry fresh snow to 21 lb per sq ft for wet, heavy snow, according to FEMA's Snow Load Safety Guide. On a 1,500 sq ft roof, that is 4,500 to 31,500 lb.
How much does ice weigh on a roof?
One inch of ice weighs a little less than 5 lb per sq ft, and a foot of ice about 57 lb per sq ft (FEMA P-957). Inch for inch, ice is much heavier than wet snow.
How much snow can my roof hold?
It depends on the design snow load the roof was built for, which is on the construction drawings or can be worked out by a structural engineer. Your building department can tell you what today's code requires; an older roof may have been built for less.
Can I measure the snow on the ground instead?
No. FEMA's guide says assuming the ground snow weight equals the roof snow load is incorrect. Roof snow load also depends on wind exposure, roof slope and shape, and how warm the building is.
When should I remove snow from my roof?
FEMA's guide says removal is prudent when the load is close to the roof's capacity, or somewhat close with more snow in the forecast. FEMA highly recommends a licensed, insured roofing contractor with snow removal experience. Leave at least 2 inches on the roof and use plastic tools to avoid damaging it.
Last reviewed 2026-10-27. See how we calculate for our sources and assumptions.