Bubble Level

Roof pitch · rise in twelve

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Waiting for sensor

RUN 12 RISE
0:12 Pitch 0.0° Angle 1.000 Rafter factor
Tap Start to read the sensor

Lay the phone along a rafter or against a gable barge board, with the top edge pointing up the slope.

Roof pitch conversion table

Rise in twelve against degrees, percent grade and the rafter length multiplier.

Pitch Degrees Percent Rafter factor Typically used for
1:12 4.8° 8.3% 1.003 Minimum fall for most membranes
2:12 9.5° 16.7% 1.014 Low-slope; standing seam metal
3:12 14.0° 25.0% 1.031 Lowest pitch for most shingles
4:12 18.4° 33.3% 1.054 Common on garages and extensions
5:12 22.6° 41.7% 1.083 Walkable; very common on houses
6:12 26.6° 50.0% 1.118 The standard residential pitch
7:12 30.3° 58.3% 1.158 About the limit for walking safely
8:12 33.7° 66.7% 1.202 Steep; roof jacks or staging needed
9:12 36.9° 75.0% 1.250 Steep pitch, good loft headroom
10:12 39.8° 83.3% 1.302 Traditional steep-roof styles
12:12 45.0° 100.0% 1.414 Equal rise and run
16:12 53.1° 133.3% 1.667 Gothic and alpine roofs
18:12 56.3° 150.0% 1.803 Very steep; heavy snow shedding

How do you measure roof pitch safely?

Measure from inside the loft where possible. A rafter has the same pitch as the tiles above it, and you can stand on the joists while you read it.

Lay the phone along the rafter with the top edge pointing up the slope, then tap Read Pitch.

Do not climb onto the roof to take a measurement. A roof steeper than about 7:12 is not safe to walk on without staging.

If the loft is boarded over, the barge board on a gable end has the same pitch and can be reached from a ladder.

What does a pitch of 6:12 mean?

The roof rises 6 units for every 12 units it travels horizontally. This equals 26.6°, or a grade of 50%.

The number 12 is a convention rather than a measurement. It works with any unit, as long as both numbers use the same one.

The run is always measured horizontally, never along the rafter. This is why a rafter is always longer than the distance it covers.

Rafter factor does this calculation for you. At 6:12 the factor is 1.118, so a run of 4 m needs a rafter of 4.47 m before you add the overhang.

Frequently asked questions

How do I convert roof pitch to degrees?

Take the arctangent of the rise divided by twelve. A pitch of 4:12 is 18.4°, 6:12 is 26.6°, and 12:12 is 45°. The table above lists every common pitch.

What is the most common roof pitch?

Most houses use a pitch between 4:12 and 6:12. This is steep enough to shed rain and snow, and shallow enough to build and work on without special equipment.

What is the minimum pitch for shingles?

Usually 3:12 with a standard installation, or 2:12 with a doubled underlay and sealed courses. Below that, use a low-slope covering. Check the specification for the product you are buying, because it varies.

Can I measure it without going on the roof?

Yes, and it is the safer method. A rafter inside the loft has the same pitch as the tiles, and a gable barge board can be reached from a ladder.

What is the rafter factor for?

It converts a horizontal run into a length of timber. Multiply the run by the factor and add your overhang. At 6:12 the factor is 1.118, so a run of 4 m needs a rafter of 4.47 m.

How precise does the reading need to be?

Not very. Roofs are built to whole or half units of rise, so a reading of 5.9:12 means a 6:12 roof. The purpose is to identify which standard pitch you have.