Snow load and roof pitch both live on the roof, but they measure different things. The roof snow load calculator estimates the weight a roof may carry from a site’s ground snow load and design factors. The roof pitch calculator converts the roof’s rise and run among pitch ratio, slope percentage, and angle — pure geometry. They meet on sloped roofs, where the snow design’s slope factor starts from the same rise/run relationship the pitch calculator reports.
What each calculator does
The roof snow load calculator takes the ground snow load (pg) from the snow load map adopted by the local jurisdiction and applies the simplified ASCE 7 flat roof equation: pf = 0.7 × Ce × Ct × Is × pg, where Ce is the exposure factor, Ct the thermal factor, and Is the importance factor. Fully exposed roofs get lower Ce values, heated structures lower Ct values, and higher risk categories higher Is values. It returns the flat roof snow load in pounds per square foot and kilograms per square meter, plus a combined-factor readout. The page notes that in ASCE 7-22 the importance factor was folded into reliability-targeted ground snow loads, and it keeps Is as an input so both editions and older IBC references can be reproduced.
The roof pitch calculator takes any one of rise and run, angle, or slope percentage and derives the others: the angle is the arctangent of rise over run, the slope percentage is 100 times rise divided by run, and the pitch ratio normalizes the rise to a 12-inch run. For example, a 6-inch rise over a 12-inch run gives 6:12, an angle of about 26.57 degrees, and a 50.0 percent slope. Results display with up to two decimals on the ratio, two on the angle, and one on the slope percentage.
Side-by-side
| Roof Snow Load calculator | Roof Pitch calculator | |
|---|---|---|
| Core question | How much snow load must the roof be designed for? | How steep is the roof? |
| Key inputs | Ground snow load, exposure, thermal, importance factors | Rise and run, or angle, or slope percentage |
| Primary output | Flat roof snow load in psf and kg/m² | Pitch ratio, angle, and slope percentage |
| Method | pf = 0.7 × Ce × Ct × Is × pg (ASCE 7 simplified) | arctan(rise ÷ run) and 100 × rise ÷ run |
| Scope | Flat or low-slope roofs; slope factors excluded | Geometry only — no structural or material claim |
| Unit handling | psf with SI equivalent (1 psf = 4.8824 kg/m²) | Unit-preserving rise/run conversions |
When to use which
Use the roof pitch calculator when you are measuring a roof and need the slope in a particular format — a material takeoff in pitch-ratio terms, an angle for a drawing, or a percent slope — or when you have one format and need the others. The result is geometry only, and the page is explicit that it does not determine roof-covering suitability, drainage design, structural capacity, access safety, or code compliance.
Use the roof snow load calculator when you are sanity-checking a snow load figure for a simple flat or low-slope building: enter the mapped ground snow load for the site and pick the factors, and the page shows the arithmetic so you can compare scenarios. Get pg from the map in the code edition your jurisdiction enforces, not from average winter snowfall totals. For a sloped roof, remember the flat roof number is the starting value — the slope factor from the roof’s pitch, plus minimum loads, drift, unbalanced, sliding, and rain-on-snow cases, belong to a licensed design professional.
Limits and disclaimer
Both calculators are educational. The snow load result is an estimate, not a structural design: minimum roof loads, slope factors, snow drift, unbalanced loading, sliding snow, and rain-on-snow are outside its simplified equation, and only a licensed design professional can certify a roof for snow. The roof pitch result is pure geometry with no structural claim. For cold-weather planning the snow load page also points to the wind chill and frost date calculators; for the roof surface itself, to the roofing calculator.