Roof Snow Load Calculator
Create a preliminary roof snow-load estimate from ground load, entered adjustment factors, plan dimensions and roof pitch.
Default project preview
21 psf
Horizontal plan area
1,200 ft²
Sloped roof area
1,341.6 ft²
Total snow weight
25,200 lb
Metric load
1.01 kPa
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Roof plan length
Enter this project assumption in ft. The current imperial default is 40 ft.
Roof plan width
Enter this project assumption in ft. The current imperial default is 30 ft.
Ground snow load
Enter this project assumption in psf. The current imperial default is 30 psf.
Exposure factor
Enter this project assumption in a unitless value. The current imperial default is 1.
Thermal factor
Enter this project assumption in a unitless value. The current imperial default is 1.
Importance factor
Enter this project assumption in a unitless value. The current imperial default is 1.
Roof and slope factor
Enter this project assumption in a unitless value. The current imperial default is 0.7.
Roof pitch rise
Enter this project assumption in per 12. The current imperial default is 6 per 12. Minimum: 0.
How to read the outputs
Horizontal plan area
load tributary area. Default preview: 1,200 ft².
Sloped roof area
6-in-12 geometry. Default preview: 1,341.6 ft².
Total snow weight
uniform plan-area estimate. Default preview: 25,200 lb.
Metric load
converted adjusted load. Default preview: 1.01 kPa.
Combined factor
all entered factors. Default preview: 0.7.
Slope factor
surface-area multiplier. Default preview: 1.118.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Preliminary roof load = ground snow load × exposure × thermal × importance × roof factor. Total weight uses the horizontal plan area, not the sloped surface area.
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 30, 2026
Convert entered ground snow load and design factors into a preliminary roof snow-load estimate while preserving the need for site-specific engineering.
Calculation steps
- 1Enter the actual project dimensions or operating values.
- 2Apply the calculator formula using consistent units.
- 3Review the unrounded result and the editable allowance.
- 4Round only to the product, stock length or equipment increment actually purchased.
Worked numerical example
A 40 psf ground load multiplied by combined exposure, thermal and importance factors of 0.8 gives a preliminary 32 psf roof load before minimums and drifting.
Purchasing and rounding
Do not use the calculated pressure to purchase or size structural members directly. Use the site-specific design snow load and applicable code procedure as inputs to structural design, including drifting, sliding, unbalanced loading and local amendments where they apply.
Interpret the result
The result is a preliminary uniform roof snow-load value from the factors entered. It is not a complete roof design load: geometry, exposure, thermal conditions, importance, drifting and minimum-load provisions can govern individual roof areas.
Page-specific assumptions
- Inputs describe one consistent project condition.
- Entered yields and efficiencies match the selected product or equipment.
- Site-specific code and engineering requirements are checked separately.
Common mistakes
- Mixing imperial and metric inputs.
- Using nominal dimensions where actual coverage controls.
- Rounding intermediate values too early.
- Treating a quantity estimate as design approval.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
FAQ
Roof Snow Load Calculator questions
Why is total snow weight based on plan area?+
Roof snow load is commonly expressed on horizontal projection, while the sloped area is reported separately for geometry.
Does this include snow drifting?+
No. Drifts at higher walls, valleys, parapets and roof steps can create much larger local loads.
Can this verify an existing roof is safe?+
No. Existing capacity requires structural evaluation of members, connections, damage and actual loading.