Roof Slope Calculator

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Roof Pitch Calculator estimates roof slope from every possible angle.

Calculate roof slope, area, rafters length and other dimensions. You can also convert roof pitch to Degrees (at the bottom).

1) Calculate Roof Slope Based On Rafters Length

Roof Span: ft. in.
Roof Rise: ft. in.

Roof Pitch = / 12″

How To Use Pitch Calculator

To estimate roof area, enter width and length (as shown in the measuring diagram below), and either Rise or Pitch – second value will auto-calculate. Click calculate. The results will pop up below the calculate button, and will include: Rafter Length, Total Size / Area, and Pitch.

Roof Measuring Diagram -

Using the diagram below, measure your roof from the ground, and enter building dimensions into the calculator #2 above. Enter the span (also known as gable side width), and the rise above the base line.

To calculate your pitch and size, measure your roof and plug in your measurements in accordance with the diagram below. Enter EITHER Roof Rise or Roof Pitch.

2) Pitch to Angle (Degrees) Calculator

Enter pitch in the first box – calculation is automatic.

Enter Roof Pitch: / 12″
Results: degrees angle

How To Measure Roof Rise

If you do not know the rise, and do not have a ladder or cannot access your roof in order to measure it, you can accurately estimate the rise by measuring 3 spans of siding.

Typical vinyl siding has 4″ exposure, so 3 spans would be equal to 12″ or 1 foot. Calculate the number of spans from the base line to the peak. Since most homes have a Rake wood, which is usually 6-8″ wide, you can add that width to the rise.

Example: If you have 19 spans of siding at 4″ exposure (width) of each span, and a 6″ rake board, the rise would be:

[6″ + (19 * 4″)] / 3 = 6′ 10″ roof rise.

measuring slope diagram

Converting pitch (US / Canadian slope measuring method) to degrees (European slope measuring method) can be useful in figuring out the roof geometry, or for European contractors who are not accustomed to th eUS system. See Table below:

roof pitch and degrees table

What Roof Type Is Best Suited For Your Roof Pitch?

If you have roof pitch of 3/13 or lower, it is highly recommended that you use/install a flat or low slope roofing (such as EPDM Rubber, PVC or TPO membrane, or Modified bitumen).

If your roof slope is above 3/12 (so called steep-slope), you can install either asphalt shingles, or a metal roof, or one of the exotic roof types: Slate, Tile, Wood, etc.

Metal roofs have the highest wind blow-off resistance, and are best suited for ice dams prevention – especially if your roof slope is below 6/12!

Average Roof Costs For:
Most Homeowners Spent Between: Most People Spent: $4,190 - $5,740 (For a 1600 sq. ft. Roof)
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While asphalt shingles are the least expensive sloped roofing material, it is more economical to get a metal roof, if you plan to stay in your home for more than 5 years.

Additional Resources

To learn additional information about why roof pitch is important and different methods of calculating it, refer to our comprehensive Roof Pitch Guide.

To get roof rafters length and accurate replacement cost, use our Rafter Calculator.

If you need to to quickly estimate how much a new roof costs, use our Roof Installation Calculator

To estimate pricing for 3-tab and architectural shingles, use our Asphalt Shingles Calculator

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43 comments on “Roof Slope Calculator

  1. Greenhouse north Boulder wall—7’
    “. South Bolder wall—5 1/2’
    Rise: 10 or 12’? That’s the question
    Span(only half side) greenhouse: 20’ 6” wide (it’s 80’ long)

    Roof wood length? That’s the 2nd question
    Because south wall is lower I don’t think these calculators work…. We need more sun…

    1. Mark,

      When you say “z-perling” do you mean metal rafters? If so, I don’t see how slope would make a difference.

      If you mean z-flashing for a standing seam roof – then for sure it’s the same for 3/12 and 6/12 and any other slope.


  2. If I have a 3 on 12 And a 40’ span across what would be lengths of the runs on each. And what is formula please

  3. I have an addition going on an existing building it’s 16 feet from the building it’s 40 feet long I have a shed roof going under the existing eve it’s 12 feet down to an 8 foot top plate what is this pitch and rafter length

  4. I have a area 17 foot by 8 foot I want to put a hip roof on it at a 5/12 pitch with a 12 inch overhang it will tie into an existing roof where there is a lean to roof tied into know what would be my materials needed to frame this up

    1. Ples,

      To frame it, just use 2x wood and anchors / fasteners per your local building code. Most likely a 2×8 rafters. If you need exact rafter lengths, use our roof rafter calculator. Keep in mind if you are tying into a roof (not into wall), rafter length should be longer (add hypotenuse of the angled roof side). If you are going into a wall, length from calculator should work for you.

      Good luck

  5. I have a 27 x 25 ft deck. I want to put a slope roof coming from the house. How much of a pitch would I need ?

    1. anything between 1/12 and 18/12 will do. Ideal is 3/12 – 7/12

      Really all depends on materials you plan to use and how much wall heghts you have above deck. if it goes straight into existing house roof, then 1/12 pitch will work with rubber or pvc roof

  6. Try to find out if I have a lean to roof
    12’ long and it’s only got an1 1/2 fall what pitch would that be on thanks

    1. Jimmy, I’m not understand your question, but basically pitch is “rise over run”

      So if you have a 12′ run and 1.5′ rise, your pitch is 1.5

  7. I have pre cut metal pans for my roof. I’m building a pole barn. My pans are 9’6″ long. I want a 4/12 pitch, with 1′ overhang. How wide will my building be?

  8. i have a 8 ft wide 8 ft high deck and am putting on a covered metal roofing that will slant to 7 ft. high. I live in Montana . What angle do i cut the 2×6 boards?

  9. Is there is a bug in the calculator ???: It is only correct only when Rise=0in.

    1) Calculate Roof Slope Based On Rafters Length

    Span: 12ft

    Rise = 1ft 0in —> Pitch = 2 /12″ – CORRECT
    Rise = 1ft 6in —> Pitch = 2.5 /12″ – INCORRECT (should be 3 / 12)
    Rise = 1ft 11in —> Pitch = 2.9166/12″ – INCORRECT (should be 3.833 / 12
    Rise = 1ft 12in —> Pitch = 3 /12″ – INCORRECT (should be 4 / 12)
    Rise = 2ft 0in —> Pitch = 4 /12″ – CORRECT

    1. Yes, 27 inch drop is correct.

      The formula would be something like this:

      12″ x pitch (3 in your case) / 12 x Base Length (not rafter length) – 12 x 3 / 12 x 9 = 27

      Or short version:

      Pitch X Base Length – 3 x 9 = 27

      Rafter length is basic Pythagorean theorem … A2 + B2 = C2, where C2 is rafter length.

      However, it’s easier to just use our rafter length calculator.

      Cheers 🙂

  10. Hi.
    I’m building a covered deck.
    The span of deck is 10 foot from house wall to end of deck. However the rafters will be 12 foot to allow for some overhang past the deck and to accommodate 12 foot TufTex roof panels (Polycarb).

    If we want the height to be at least 7’6″ at end of deck. The height of starting position would be 9’6″. Does that mean 4:12 pitch? (2 foot rise – 4inches every foot).

    I’m confused with few things.
    1. The deck span is 10 foot. But the rafters will be 12foot
    2. I’ll like the rafters to end about 1 foot past the headers of deck which will be at 7’6″.

    I feel like I’m looking at wrong information to calculate the roof pitch.

    1. Noel,

      So if your gable end is 28′ wide, with 5 rise, your pitch is 4.285714285714286 … round up to 4.3 / 12

      We actually have a tool for that – rafter length calculator. I recommend you try it. Here are the numbers I got from that tool:

      You will (most likely) need a 16 feet rafter length, assuming you have overhangs that are LESS than 13″ (1 foot 1 inch) on each side.

      If your overhangs are 1′ 2″ or more, up-to 5′ – you will need a 20′ rafter length. I’ve never seen overhangs wider than 3-4′ thought 🙂

      Both 16′ and 20′ rafters are available in regular pine 2x wood from lumber yards and Home Depot / Lowe’s etc.

      If you go over 20′, you will need LVL or engineered lumber, which is much more expensive. But in your case that is not necessary, because I don’t suppose you will have overhangs that over 5′.

      Good luck

  11. Hi I’m building a shed 24ft by 8ft and 7ft high, I’m using fiber cement roof slates but need my roof pitch has low has I can get it, can you please tell me how high I can go on the hight from sole plate to hight of roof, I hope this makes sense.
    A novice

  12. Hi,
    I need to calculate a minimum 5 degree pitch over 3600 ml length. The height of the highest point is 2500 ml, and I want to calculate my post height.

  13. If the slope of your roof is greater than 6° rising
    to horizontal 12°, better opt for the roofing brackets or boards.

    1. PA,

      If we use that logic, then 24 pitch roof should be 90 degrees, right (12*2 same as 45 degrees * 2)? But it’s not. It’s about 63.5 degrees. Like I said – it is not a straight line. Each step is smaller than the previous one. Look at last diagram:

      Roof pitch to degrees conversion table

      1 pitch is 4 degrees.
      2 pitch is 9.5 degrees – that’s a 5.5 degrees step.
      3 pitch is is 14 degrees – that is a 4.5 degrees step.

      from there it slowly declines or stays the same…

      However, those are not exact numbers – it’s more like 14.04 degrees for a 3 pitch.

    2. These roof pitches are treated as right triangle, and by applying the theory, the inverse tangent of 6/12 is actually 26.565 degree.

    1. Pa,

      Quick answer – because it is not a straight line increase of 3.75 degrees, for each 1/12″. I will look into why you are getting “NaN”

      1. The NaN issue happens when a user enters ” after the number in the input text box. These types of characters should not be allowed as input. Hope that helps.