Roof Snow Load Calculator
Measure the depth on the roof, say what the snow is like, and this gives the load in pounds per square foot and the total weight sitting up there — with a plain reading of whether that is a lot.
Take this list to the store
We'll email the quantities above, what you typed in, and a link that reopens this calculator already filled in — so you can adjust it on your phone in the aisle.
How to work it out
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Measure the depth on the roof
Not the depth on the ground — wind strips some roofs bare and piles drifts on others. Measure from a window or with a snow rake, at a spot away from drifts, and again at the deepest drift.
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Judge the snow
Fresh powder is about 0.26 lb per square foot per inch. Settled snow is double that. Snow that has thawed and refrozen, or taken rain, can be four or five times heavier for the same depth.
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Compare with the design load
Every roof is built for a ground snow load set by local code. Ask your building department, or look at the original plans. 20 to 70 lb per square foot covers most of the snowy states.
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Watch the warning signs
Doors that stick, new cracks in drywall, sagging ceilings or creaking are reasons to get out and call someone, whatever a calculator says.
What snow weighs
Pounds per square foot, by depth and type.
| Depth | Fresh | Settled | Packed | Wet |
|---|---|---|---|---|
| 6 in | 1.6 | 3.0 | 5.4 | 7.5 |
| 12 in | 3.1 | 6.0 | 10.8 | 15.0 |
| 18 in | 4.7 | 9.0 | 16.2 | 22.5 |
| 24 in | 6.2 | 12.0 | 21.6 | 30.0 |
| 36 in | 9.4 | 18.0 | 32.4 | 45.0 |
| 48 in | 12.5 | 24.0 | 43.2 | 60.0 |
Rough ground snow loads
Typical design values. Your local figure is what counts — these are for orientation only.
| Region | Ground snow load |
|---|---|
| Gulf coast and the deep south | 0–5 lb per sq ft |
| Mid-Atlantic and lower Midwest | 20–30 lb per sq ft |
| Great Lakes, New England inland | 40–60 lb per sq ft |
| Northern New England, mountain west | 60–100 lb per sq ft |
| High mountain and lake-effect belts | 100+ lb per sq ft |
How much does snow weigh?
Water weighs 5.2 lb per square foot per inch of depth. Snow is water plus air, so its weight depends entirely on how much air is in it.
Fresh powder is roughly a twentieth of water — about 0.26 lb per square foot per inch. A foot of it is only 3 lb per square foot. The same foot after a thaw and a refreeze can be 11 lb, and after rain closer to 15.
Depth is not the danger — water content is
Two feet of powder is lighter than eight inches of slush. That is why roofs fail after rain-on-snow events rather than after the big pretty snowfall.
Ice dams add to it in the worst place: at the eaves, over the wall line, where the roof is already carrying the most.
Drifts and valleys
Wind does not lay snow evenly. It scours the windward slope and dumps it in the lee, against dormers, behind chimneys and in valleys where two roofs meet.
A drift can hold two or three times the flat-roof depth, and that is where most structural failures start. Measure the drift as well as the field.
Clearing it safely
Use a roof rake from the ground, working from the eave upward, and leave a couple of inches so you are not scraping shingles. Do not climb onto a snow-covered roof, and never use a shovel or an axe on ice dams.
If the load is near the design figure and you cannot clear it safely, call a roofer or a contractor. A structural engineer is cheaper than a roof.
How this is worked out
No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.
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load = depth × pounds per sq ft per inchWeight depends on the water in the snow, not the depth alone. -
total = load × roof areaWhat the whole structure is carrying. -
headroom = (design load − current load) ÷ weight per inchHow many more inches of this snow the roof was built to take.
Common questions
How much does a foot of snow weigh?
About 3 lb per square foot if it is fresh and light, 6 if it has settled, and up to 15 if it is wet or has taken rain.
How much snow can a roof hold?
Most US roofs are designed for 20 to 70 lb per square foot depending on the region. At a 30 lb design load that is roughly 10 ft of fresh powder, 5 ft of settled snow, or 2 ft of wet snow.
When should I clear snow off my roof?
When the load approaches the design figure, when rain is forecast onto deep snow, or at any sign of strain — sticking doors, new cracks, sagging or creaking.
Does roof pitch matter?
Yes. Steep roofs shed snow and carry less of it; low-slope and flat roofs hold everything that lands. Codes reduce the design load with pitch for that reason.
Is ice worse than snow?
Much worse by depth — solid ice is 5.2 lb per square foot per inch, twenty times fresh snow. An ice dam a few inches thick concentrates a lot of weight at the eaves.
What is ground snow load?
The design snowfall weight for your location, set by code maps and adjusted by the roof's shape and exposure. Your building department has the number for your address.
How do I measure snow depth safely?
From a window, from a ladder at the eave, or with a marked snow rake handle. Do not walk on a loaded roof to measure it.
Where these figures come from
Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.
- ASCE 7, Minimum Design Loads for Buildings — ground snow load mapping and roof load factors
- FEMA Snow Load Safety Guide — snow density figures and warning signs of overload
- National Weather Service snow water equivalent data — typical water content of fresh, settled and wet snow
Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 27, 2026.