Roof Pitch Calculator

Figure Out Your Roof's Pitch Without Climbing Up There Twice

Every roofing job starts with the same question: how steep is this roof, actually? A pitch of "6/12" doesn't mean much until you can picture it, and framers, roofers, and building inspectors all tend to talk about slope in different units — rise-over-run, degrees, or percent grade. This calculator converts between all of them at once, so whatever number you were given (or measured with a level and tape), you get the rest for free, plus the rafter length you'll need to cut for a given span.

How to use it

• Pick how you know your roof's slope: rise & run (e.g. "6 inches over 12"), a pitch ratio like 6/12, an angle in degrees, or a percent grade from a survey.
• Enter that one value and every other format — pitch ratio, angle, grade, and the roof slope factor — updates instantly.
• If you know the horizontal run (half the building width, typically), add it along with any overhang to get the actual rafter length to cut.
• Check the reference table below to see how your pitch compares to common residential slopes.

Real-world use cases

A framer given a plan that lists "4/12" needs the angle in degrees to set a speed square or saw angle — this converts it instantly. A DIYer who measured a 24° angle off an existing roof can find the matching pitch ratio to order the right rafter brackets. Someone comparing a contractor's quote against manufacturer specs can check whether a proposed pitch is steep enough for standard asphalt shingles (most require at least 2/12, with 4/12 or steeper recommended).

Frequently asked questions

What's the difference between roof pitch and roof slope?

They describe the same thing in different formats. Pitch is usually written as a ratio like 6/12 (6 inches of rise per 12 inches of run), while slope can refer to the angle in degrees or the percent grade — this tool shows all three side by side.

How do I calculate roof pitch from an angle?

Take the tangent of the angle and multiply by 12 to get the "X" in X/12. Enter the angle in degrees above and the pitch ratio is calculated for you automatically.

What is the minimum roof pitch for shingles?

Most asphalt shingle manufacturers require a minimum of 2/12, and recommend 4/12 or steeper with standard underlayment. Anything under 2/12 generally needs a low-slope or membrane roofing system instead.

How is rafter length calculated from pitch?

Rafter length equals the horizontal run multiplied by the roof slope factor (the hypotenuse-to-run ratio for that pitch). A steeper pitch means a larger slope factor and a longer rafter for the same horizontal span.

Does a steeper roof pitch need more shingles?

Yes — the actual roof surface area is larger than the building's footprint by the slope factor shown above. A 45° (12/12) roof needs about 41% more material than a flat one covering the same footprint.