Roof Snow Load Calculator: Snow Weight Per Square Foot and Total Pounds
Estimate roof snow weight per square foot and in total pounds from snow depth and density or melted water, add ice, and compare it to a design load you enter.
How this is calculated
Snow load is depth times density. A pound per cubic foot spread one inch deep weighs one twelfth of a pound per square foot, so the snow load in psf is the depth in inches times the density in lb/ft³, divided by 12. The melted-water mode skips the density: an inch of water weighs 5.2 psf, so the water from a full-depth sample times 5.2 is the snow load directly.
depth mode: snow psf = depth (in) × density (lb/ft³) ÷ 12
water mode: snow psf = melted water (in) × 5.2
ice: ice psf = ice thickness (in) × 5.2
total psf = snow psf + ice psf
total lb = total psf × roof footprint (sq ft)
implied density (water mode, depth known) = snow psf ÷ depth × 12
water content = density ÷ 62.4 (62.4 = 5.2 × 12)
share of design load = total psf ÷ the design load you typedWorked example (the defaults). Bend's own example: 20 inches of snow at its 1.25 psf per inch rule is 25 psf. On a 1,500 sq ft footprint that is 37,500 lb, about 18.75 US short tons. Add half an inch of ice at 5.2 psf per inch and the load is 27.6 psf, or 41,400 lb. If the design load on the plans were 30 psf, the estimate would be 92% of it, which is a ratio and nothing more.
The figures and where each comes from.
Figure Source
1.25 psf per inch at 25% moisture (15 lb/ft³) City of Bend, Oregon
Snow 1 to over 21 lb/ft³ City of Bend, Oregon
Saturated snow about 20 lb/ft³ City of Bend, Oregon
Ice 5.2 lb per sq ft per inch City of Bend, Oregon
1 in of water = 5.2 psf Town of West Boylston, MA
1 lbf/ft² = 47.88026 Pa; 1 lb/ft³ = NIST SP 811, Appendix B.9
16.01846 kg/m³; 1 lb/ft² = 4.882428 kg/m²Two sources, one small gap, shown side by side. Bend publishes 1.25 psf per inch for snow at 25% moisture. Taking 25% of West Boylston's 5.2 psf per inch of water gives 1.3. The density preset uses Bend's published 1.25; the melted-water mode uses West Boylston's 5.2 as published. If you have weighed or melted a sample, that measurement beats either rule.
What is not pre-filled. No design load appears on this page: it belongs to the building, and comes from its plans, its permit, a manufactured home's certification label or the building official. The 1,500 sq ft footprint is an example. Densities other than the four Bend presets are yours to enter.
A weight is the reason for the call, not the price of it. When the roof work is yours to quote, the snow removal pricing calculator builds the job price, and the snow removal contract template puts the scope in writing.
How much does snow weigh on a roof?
Multiply the depth by the density. The City of Bend, Oregon’s rule of thumb is 1.25 lb per square foot for each inch of snow at 25% moisture, so 20 inches weighs about 25 psf. Bend puts snow anywhere from about 1 to over 21 lb per cubic foot, and ice at 5.2 lb per square foot per inch. Melt a full-depth sample for a better figure: West Boylston, MA counts each inch of water as 5.2 psf.
The weight is the number that starts the conversation, whether that is a property manager deciding to call a crew or a crew deciding how to quote the job. It is not the number that ends it. Only the building official or a licensed engineer can say what a particular roof should carry, and this page never tries to.
Snow weight per square foot by depth and density
One pound per cubic foot spread one inch deep weighs a twelfth of a pound per square foot, so the load is depth in inches times density divided by 12. The table is that arithmetic on the densities the City of Bend publishes:
| Depth on the roof | Light, about 1 lb/ft³ | Bend rule, 15 lb/ft³ | Saturated, about 20 lb/ft³ | Top of range, 21 lb/ft³ |
|---|---|---|---|---|
| 6 in | 0.5 psf | 7.5 psf | 10 psf | 10.5 psf |
| 12 in | 1 psf | 15 psf | 20 psf | 21 psf |
| 24 in | 2 psf | 30 psf | 40 psf | 42 psf |
| 36 in | 3 psf | 45 psf | 60 psf | 63 psf |
Read across a row and the problem is obvious. The same two feet of snow can weigh 2 psf or 42 psf. Depth alone tells you very little; the density column is where the answer lives, and the only way to know which column you are in is to sample the snow.
Bend’s 1.25 psf per inch is a rounded rule. Taking 25% of West Boylston’s 5.2 psf per inch of water gives 1.3, so the two sources sit a few percent apart at the same moisture. The calculator’s preset uses Bend’s 1.25 as published, and the melted-water mode uses West Boylston’s 5.2 as published, so you can see both.
The melted-water method
West Boylston’s building department describes a field check: push a can down through the snow to the roof surface, empty and refill it until you reach the roof surface, melt it, and measure the water. “Depth of inches multiplied by 5.2 = psf.” Four inches of water is 20.8 psf, whether it came from a foot of wet snow or three feet of powder. Enter the snow depth too and the calculator reports the density and water content your sample implies.
The two towns describe the moisture range slightly differently. Bend says snow moisture runs from about 1% to about 33%; West Boylston says 3% for very dry snow to 33% for wet, heavy snow, and nearly 100% for ice. Both put the heavy end near a third water, which is why Bend’s saturated figure of about 20 lb per cubic foot is close to a third of the 62.4 lb per cubic foot that 5.2 psf per inch implies for water.
If you have a scale, Bend offers a third route: weigh a 12 in by 12 in square of snow cut from the roof. The pounds read directly as pounds per square foot.
Ice, rain and uneven snow
Ice goes on top of the snow figure. Bend’s instruction is to “Use 5.2 lbs for every inch in thickness,” so the calculator keeps it on its own line. Rain is the other fast change: Bend warns that “If we receive excessive rainfall, the weight of the roof snow can increase rapidly,” and that “Flat roofs are more of a concern (Less than 3/12 pitch).”
The result assumes a uniform depth across the footprint. Real roofs are not uniform. West Boylston notes that flat, gable, shed and gambrel roofs, and roofs with multiple valleys and snow gathering points, change how the weight sits, so measure the deepest drift and the valley as well as the open field of the roof. Use the footprint (the plan area) rather than the sloped surface, because loads are stated per horizontal square foot.
What a design load is, and who says what yours is
A design load is the snow load a roof was built to carry, and it belongs to the building, not to a calculator. Bend states that buildings it permitted are “designed for 20-25 lbs. /sq. ft. minimum roof snow load” depending on their age, and that “Until recently, manufactured homes were designed for a roof snow load of 30 lbs/sq ft,” with the figure on the home’s certification label. Those are one city’s figures for its own buildings, not a number to assume for any other roof.
The calculator will put your estimate next to a design load if you type one in from the plans, the permit, the label or the building official, and it shows the ratio as plain arithmetic. It does not supply a design load and it does not turn the ratio into a verdict. Bend is direct that “the City of Bend does not make recommendations on when to remove snow from roofs,” and that “It is up to the individual property owner to consider the benefits and dangers of snow removal.” It also asks owners to “be aware of the potential dangers of shoveling or raking snow from a roof.”
For crews quoting roof snow removal
A weight estimate is a reason for the call and a record of what you found, not the price of the job. Build the price with the snow removal pricing calculator, put the scope, the access and the exclusions in the snow removal contract template, and log the depth, the estimate and the before-and-after photos on each visit with the snow and ice service log template. If the same truck also plows the lot, the parking lot plow time estimator sizes that part of the stop. Every snow and landscape calculator sits on the lawn and landscape hub.
Frequently asked questions
How much does snow weigh on a roof per square foot?
How do I measure the weight of snow on my roof without a scale?
How much weight does ice add to a roof?
Can this calculator tell me whether my roof will hold the snow?
Sources
- Roof load and structural integrity (news release, February 26, 2019): "1.25= Weight of 1 sq ft of snow for each 1” of depth"; "This calculation uses a 25% moisture density"; snow "can weigh from about 1 pound per cubic foot to over 21 pounds per cubic foot"; "saturated snow weighs about 20 pounds per cubic foot"; for ice, "Use 5.2 lbs for every inch in thickness"; "please consult a licensed architect or engineer to assess the integrity". City of Bend, Oregon. Retrieved .
- Calculating Snow Loads on Roofs (Building Department): "An inch of water depth weighs 5.2 psf"; "The water content of snow may range from 3% for very dry snow to 33% for wet, heavy snow to nearly 100% for ice"; "Depth of inches multiplied by 5.2 = psf". Town of West Boylston, Massachusetts. Retrieved .
- NIST Guide to the SI, Appendix B.9: "pound-force per square foot (lbf/ft2) pascal (Pa) 4.788 026 E+01"; "pound per cubic foot (lb/ft3) kilogram per cubic meter (kg/m3) 1.601 846 E+01"; "pound per square foot (lb/ft2) kilogram per square meter (kg/m2) 4.882 428 E+00". National Institute of Standards and Technology. Retrieved .