How to find roof pitch

By Dexaloop · Updated 27 October 2026 · Checked against the sources listed below

Roof pitch is how many inches a roof rises for every 12 inches it runs level, written as rise/12. To find it, hold a level horizontally against a rafter, measure 12 inches along the level, then measure straight up from that point to the underside of the rafter. If that gap is 6 inches, the roof is a 6/12 pitch, which is 26.57 degrees and a 50% slope. You can do this from the attic or a ladder at the gable end, without walking on the roof. The rest of this guide shows how to convert pitch to degrees and percent, and how to use pitch to find the true area of a roof.

Three ways to measure pitch safely

1. From the attic. This is the safest method. Place a 24 inch level against the underside of a rafter, hold it level, and mark the level at 12 inches from the end touching the rafter. Measure straight up from the 12 inch mark to the rafter. That measurement is the rise.

2. From a gable end. On a ladder at the side of the house, hold the level against the bottom edge of the rake board or fascia and measure the same way.

3. From the plans. House plans usually show pitch as a small triangle with 12 on the level side and the rise on the upright side. If the plans give total rise and total run instead, divide: a roof that rises 4 ft over a 12 ft run is 4 / 12 x 12 = 4/12.

A phone level or angle finder placed on a rafter gives degrees directly. Convert degrees to pitch with the formula below.

Pitch, degrees and percent

Every way of describing slope comes from the same right-angled triangle, with the run as the level side and the rise as the upright side.

• Pitch = rise for a 12 inch run, written rise/12.
• Percent slope = rise / run x 100. A 6/12 is 50%.
• Degrees = arctangent of (rise / run). A 6/12 is the arctangent of 0.5, which is 26.57 degrees.
• Degrees to pitch = tangent of the angle x 12. A 30 degree roof is 0.577 x 12 = 6.93, close to 7/12.

In a spreadsheet, the ATAN function returns the angle in radians. Microsoft's help page says to "multiply the result by 180/PI( ) or use the DEGREES function" to get degrees. So =DEGREES(ATAN(6/12)) gives 26.57.

Roof pitch table

The pitch multiplier and why it matters

A sloped roof has more surface than the flat footprint under it. The pitch multiplier tells you how much more. It is the length of the sloping side of the triangle when the run is 1:

Multiplier = square root of (1 + (rise / 12) x (rise / 12))

For a 6/12 roof: 6 / 12 = 0.5, 0.5 x 0.5 = 0.25, 1 + 0.25 = 1.25, and the square root of 1.25 is 1.118. Every level foot becomes 1.118 feet along the roof.

Worked example: roof area

A house footprint, including the overhangs, is 40 ft by 30 ft, so 1,200 square feet seen from above. The roof is 6/12.

1. Roof surface: 1,200 x 1.118 = 1,341.6 square feet.
2. Roofing squares: NIST lists the building "square" as 100 square feet, so 1,341.6 / 100 = 13.42 squares.

Using the footprint without the multiplier would have under-ordered by about 142 square feet. On an 8/12 roof the gap is larger: 1,200 x 1.202 = 1,442.4 square feet.

Worked example: rafter length

A gable roof spans 24 ft wall to wall, so each side runs 12 ft level. At 6/12, the rafter's sloping length is 12 x 1.118 = 13.42 ft, about 13 ft 5 in, before adding overhang and before the cuts at the ridge and the wall. Treat this as a line length for planning, not a cut list.

Low slope and steep slope coverings

Pitch decides which roof coverings are allowed. Building codes set a minimum slope for each covering. A summary in Professional Roofing, the magazine of the National Roofing Contractors Association, lists these minimums from the 2018 International Building Code:

The same article says the 2018 International Residential Code is similar but "indicates a 3:12 minimum roof slope for wood shakes." Code minimums are not the same as good practice. For asphalt shingle, tile, metal shingle, slate and wood shake and shingle roofs, the article states: "NRCA recommends slopes of 4:12 or more." It adds that "NRCA's recommendations are best practice guidelines." So a 2:12 shingle roof can meet code while sitting well below what the roofing trade advises. Codes are revised every few years and adopted locally with changes, so check the edition your city or county uses, and follow the maker's installation instructions, which can be stricter than code.

Common mistakes

• Measuring along the rafter instead of level. The 12 inches must be horizontal, or the pitch reads low.
• Mixing units. Rise and run must use the same unit. A rise of 2 ft over a run of 8 ft is 24 inches over 96 inches, which is 3/12. Convert both to inches first, or the answer will be wrong.
• Using the footprint as the roof area. Multiply by the pitch multiplier.
• Confusing percent and degrees. A 100% slope is 45 degrees, not 90.
• Climbing on the roof to measure. The attic or a ladder at the gable gives the same answer.

Once you have the rise, the calculator below converts it to degrees, percent and the multiplier, and works out rafter length and roof area.

Questions

Sources

• Professional Roofing (National Roofing Contractors Association): Roof slope guidelines, Mark S. Graham, August 2018
• NIST Handbook 44 (2026), Appendix C: General tables of units of measurement
• Microsoft Support: ATAN function

This guide is general information, not legal, tax or financial advice. Rules change; check the official source for your own case. Found a mistake? Email support@dexaloop.com.

Related tools

• Roofing calculator
• Square footage calculator
• Stair calculator

More home projects guides

• How much mulch or gravel do I need?
• How much paint do I need?
• How to calculate cubic yards
• How to calculate square footage