A roof snow load calculator helps homeowners and contractors estimate the total weight of accumulated snow on a roof — a critical safety check after heavy snowfall. Snow density varies widely by type: fresh powder can weigh as little as 5 lbs per cubic foot while wet, packed snow exceeds 30 lbs/ft³. Combined with roof area and pitch, these figures reveal whether your structure is approaching its load limit.
Snow Load Calculator
Leave blank to use the 20–40 psf residential default range for safety assessment.
How to Calculate Roof Snow Load
Heavy snowfall is one of the most serious seasonal threats to residential and commercial structures. Understanding your roof snow load helps you decide when to take action — whether that's hiring a professional to remove snow, staying vigilant for warning signs, or simply monitoring the situation. This free snow load calculator walks you through the entire process.
Step 1: Enter Your Roof Area
Start by entering your roof's footprint area — the horizontal area the roof covers, not the sloped surface area. You can either type the total square footage directly, or use the Length × Width mode if you know your house dimensions. For a rectangular house that is 50 feet long and 30 feet wide, the footprint is 1,500 sq ft. For L-shaped or irregular plans, estimate the total covered area as closely as possible.
Step 2: Measure Snow Depth
Use a ruler or yardstick inserted vertically into the snow on your roof to measure depth in inches. Take several readings across different parts of the roof and use an average — snow tends to drift, so corners and low spots accumulate more than the center. If you cannot safely access your roof, measure ground-level snow in a sheltered spot and use that as a conservative proxy. Remember: even a foot of light snow adds measurable weight, and a foot of wet snow can be dangerous.
Step 3: Select Snow Type
Snow density varies dramatically. Light, fluffy snow from a cold powder storm weighs as little as 5 lbs per cubic foot. Fresh average snow is around 12.5 lbs/ft³. Packed snow that has been sitting for days and compacted by additional snowfall weighs 15–30 lbs/ft³. Wet, heavy spring snow can reach 40 lbs/ft³. Ice from a freezing rain event weighs about 57 lbs/ft³ — nearly twelve times lighter snow. If you are unsure, select "Fresh Snow" as a reasonable starting point, or use the custom density option if you know the specific weight.
Step 4: Choose Roof Pitch
Steeper roofs shed snow naturally through gravity and heat loss, so they accumulate less load than flat roofs. The ASCE 7 standard uses a slope factor (Cs) that equals 1.0 for pitches up to about 2:12 (no reduction), then decreases linearly to zero at roughly 70° (12:12 and above). Our snow load calculator applies this Cs factor automatically based on the pitch you select. A 6:12 pitch (common in residential construction) has a Cs of approximately 0.5, meaning it accumulates roughly half the snow load of a flat roof under the same conditions.
Step 5: Review Results and Safety Assessment
The calculator displays the total snow weight in pounds and tons, plus the critical metric: load in pounds per square foot (psf). Most residential roofs built to modern codes are designed for 20–40 psf snow load, though this varies significantly by region and building age. The safety assessment compares your calculated load against this range. If your load is approaching or exceeding 20 psf, consider contacting a professional. Above 30 psf on an older structure is a serious concern. Watch for physical warning signs: unusual creaking, sticking doors or windows, and visible sagging are signs that structural limits may be near.
Frequently Asked Questions
Is this snow load calculator free to use?
Yes, completely free with no signup required. All calculations run locally in your browser — your roof measurements and snow data are never sent to a server or stored remotely.
Is my data private?
Absolutely. Everything runs in your browser. Your roof dimensions and location data never leave your device. No cookies, no tracking of project data, no account required.
How much snow load can a residential roof handle?
Most residential roofs built to modern codes are designed to handle 20 to 40 pounds per square foot (psf) of snow load, depending on region. Older homes, flat roofs, and structures in high-snow regions may have lower or higher limits. When in doubt, consult a structural engineer or your local building department.
When should I shovel snow off my roof?
Consider shoveling when the snow load exceeds 20 psf, when you hear creaking or cracking sounds, when doors or windows become hard to open, or when you see sagging ridgelines or rafters. Wet or packed snow is far heavier than fresh powder — 6 inches of wet snow can equal the weight of 24 inches of fresh snow.
How heavy is snow per cubic foot?
Snow density varies significantly by type. Fresh light snow weighs about 5–8 lbs per cubic foot. Average fresh snow is around 12–15 lbs/ft³. Packed snow weighs 15–30 lbs/ft³. Wet or heavy snow runs 20–40 lbs/ft³. Ice is the densest at roughly 57 lbs/ft³. This calculator uses standard midpoint values for each type.
Does roof pitch affect snow load?
Yes. Steeper roofs shed snow more readily, so the actual snow accumulated is less than on a flat roof. ASCE 7 uses a slope factor (Cs) that equals 1.0 for pitches up to 2:12, then decreases linearly for pitches between 2:12 and 12:12, reaching 0 at about 70°. This calculator applies the Cs slope reduction factor based on your selected pitch.
What is ground snow load and how does it relate to roof load?
Ground snow load (pg) is the weight of snow on flat ground in your region, measured in pounds per square foot. Roof snow load is calculated from ground load using: Roof Load = pg × Ce × Ct × Cs × I. For a typical heated residential building with flat terrain and occupancy importance factor of 1.0, roof load ≈ ground load × Cs. ASCE 7 and local building codes publish ground snow load maps by location.
What are the warning signs of too much snow on a roof?
Key warning signs include unusual creaking, popping, or cracking sounds; doors or windows that suddenly stick or won't close properly; visible sagging in the roof deck, ridge, or eaves; cracks in interior walls or ceilings; and in severe cases, bowed or split rafters visible from the attic. If you notice any of these signs, remove snow immediately and consult a structural professional.