How to Find the Pitch of a Roof

Roof Pitch Calculator

Last updated:

Sep 30, 2021

Table of contents:

What is the roof pitch?
How to calculate roof pitch?
Roof slope calculator – example of use
FAQ

This roof pitch calculator is a handy tool that will help you quickly assess the pitch of your roof and what length rafters you need for your construction works. We will explain to you how to determine the roof pitch step by step. You can also use this roof slope calculator to recalculate the roof pitch from degrees to percents.

What is the roof pitch?

Roof pitch is simply the slope created by the rafter. It can be assessed in two ways – either as the angle the rafter makes with the horizontal or the proportion between the rise and the run of the roof.

Roof pitch is often expressed as a ratio between rise and run in the form of x:12. For example, a pitch of 1:12 means that for every twelve yards of building length, the rise will be equal to one yard.

We can divide roofs into the following categories:

Flat roofs are not perfectly flat in reality – they need a small slope for water runoff. Generally, these roofs have a pitch from 1/2:12 to 2:12 (from 4.2% to 16.7%).
Low pitched roofs have the pitch below 4:12 (33.3%). These are generally difficult to maintain, as they require special materials to avoid leaks.
Conventional roofs have the pitch ranging from 4:12 to 9:12 (33.3% to 75%). They are the easiest ones to construct, and they are safe to walk on.
High-pitched roofs often require additional fasteners. They have a pitch that can be as high as 21:12 (175%).

How to calculate roof pitch?

Generally, roof pitch is calculated from the same formula that describes a right triangle. You can use the following equations to find the length of the rafter and the slope:

rafter² = rise² + run² (from the Pythagorean theorem);
rise / run = pitch, where pitch is expressed in percent; and
pitch = tan (angle), where angle is the roof pitch expressed in degrees.

If you want to find the roof pitch in the form of x:12, simply calculate the pitch and substitute 12 for the run length. The value displayed as the rise will be your x.

Roof slope calculator – example of use

Measure the run length – it is the horizontal distance between the roof ridge and the wall of the building. Let's assume it is equal to 6 m.
Measure the rise of your roof. Let's say it is equal to 1.5 m.
Calculate the rafter length, substituting these values into the following formula:

rafter² = rise² + run² = 1.5² + 6² = 2.25 + 36 = 38.25

rafter = √38.25 = 6.18 m
Calculate the roof pitch as the proportion of rise and run:

pitch = rise / run = 1.5 / 6 = 25%
Recalculate this value into an angle:

angle = arctan(pitch) = arctan(0.25) = 14°
Finally, you can find the roof pitch in the form of x:12.

x = pitch * 12 = 0.25 * 12 = 3
The pitch of your roof is 3:12. It can also be written down as 25% or 14°.

FAQ

What is the standard pitch for a roof?

There is no standard, universal roof pitch. Roof pitch varies depending on culture, climate, style, and available materials. In the USA, the range of standard pitches is anywhere between 4/12 and 9/12. In the UK, the typical house has a pitch between 40°-50° – although 45° should be avoided.

Contemporary houses often have 'flat roofs' which shouldn't be completely flat but should be around 1:40. In Italy, with its more temperate climate, the range of angles is 16-25.

What is the average quote for getting a roof pitched?

There are a lot of factors that will affect how much getting your roof pitched will cost – design, style, accessibility, cost of labor etc. In the USA, you can expect to pay between $3.19-$4.43 per sq.ft. for asphalt shingles. If you choose another material, such as metal or wood, the range is $7.35-$10.73 per sq.ft.

In the UK, the price of getting a roof fitting is £72-£75 per square meter. These are only estimates though, talk to your neighbors to see what roofing costs in your area.

What is the minimum roof pitch for snow?

The minimum roof pitch for shedding snow is around 30°, or a 6:12 or 7:12 slope. However, this is not a definite, as the material of your roof, the direction of the snow and wind are some factors that can affect whether or not snow will slide, as roofs of as little as 10° have been reported to shed snow. Roofs of steeper pitches will likely retain less snow, so, if you live in snow-prone regions, a steeper pitch is highly desired.

What is a 4/12 roof pitch?

A 4/12 is a roof slope that rises by 4 inches for every 12 inches across. This forms an angle of 18.5° between the horizontal section and the roof, and creates a gentle incline that is seen as a midpoint between a low-pitch and medium-pitch roof. A 4/12 slope is enough to accommodate water runoff, but is not suitable for regions that are affected by heavy snowfall. Standard asphalt and composition shingles are the best for a 4/12 roof; rubber and wood shingles are unsuitable.

What is the best pitch for a roof?

The best roof pitch depends on the style of roof you are going for. If you are looking for a sleek, modern style, a (not entirely) flat roof with a pitch of 1:40 should be used.

For a Gothic style, the rafters must equal the span (60°), while an Elizabethan style requires the rafters to be longer than the span.

In snowy areas, your roof should be at least 10/12 (40°) to allow snow to shed, while the safest roof pitch in very windy areas is between 4/12-6/12 (18.5°-26.5°).

What is the smallest pitch of a roof?

The smallest pitch of a roof is 0.5/12. A completely flat roof is a poor design, as water and snow will collect on it, eventually leading to your roof collapsing in from the weight of it all.

A common choice for flat roofing material is EPDM rubber, as it is highly durable, waterproof, and can be made from recycled materials. Flat roofs also tend to be cheaper and require less maintenance than traditional roofing, making them a perfect addition to your home.

What roof pitch is 30 degrees?

A 30° roof pitch is roughly the same as a 7/12 roof pitch. To convert from degrees to the American ratio:

Find the tangent of the angle, tan(angle). This gives you the pitch of the roof.
Multiply the pitch by 12 to find the x in the ratio x/12.
Check your results with the Omni Roof Pitch Calculator.
Enjoy having one less thing to worry about.

What is a roof pitch multiplier?

A roof pitch multiplier, also known as a roof pitch factor, is a number that, when multiplied by the area covered by a sloped roof, gives the actual area of the roof. The math behind this number is that it is the square root of ((rise/run)² + 1). Roof pitch multipliers are extremely useful in estimating the amount of material required to fit your new sloped roof, as conventional mathematics will leave you short!

What degree angle is a 12 12 pitch roof?

A 12/12 pitch roof has a pitch angle of 45°. To convert between American roofing ratios and pitch degrees, follow these steps:

Divide the first part of the ratio by 12 to work out the pitch.
Find the inverse tangent of the pitch to find the angle in degrees.
Check your results with the Omni Roof Pitch Calculator.
Marvel at your mathematical prowess.

What roof pitch is walkable?

A roof pitch of 6/12 (26.5°) or less is considered easily walkable, and no extra precautions are required. A roof of pitch 7/12 (30°) is manageable, but caution should be taken. Pitches between 8/12 and 10/12 (33°-40°) are also considered walkable, but it is not advisable and, if you have to walk on these roofs, extreme caution should be taken. Roofs any steeper than this are considered not walkable, and special equipment or scaffolding is required. Please do not take risks on roofs, as the fall can be fatal.

Can you shingle a 3/12 pitch roof?

You can shingle a 3/12 pitch roof, but special application measures should be taken to prevent leakages at some point down the line. Some kind of protective, waterproof membrane should be put down underneath the shingles, as well as using shingles that are recommended by the manufacturer for that slope. You can find this information on the shingle packaging. This issue with these low sloped roofs comes from the flow of water not being quick enough to prevent water from flowing under the shingle and into your ceiling.

Bogna Szyk

How to Find the Pitch of a Roof

Source: https://www.omnicalculator.com/construction/roof-pitch

Brigden Eiried