What pitch means

Roof pitch is the number of inches a roof rises for every 12 inches it runs horizontally. A 6/12 roof climbs 6 inches over each foot of run. Pitch decides which materials you can use, how much area you need to cover and whether the roof is safe to walk.

For example, asphalt shingles are only allowed on roofs of 2/12 or steeper, and slopes between 2/12 and 4/12 need a double layer of underlayment under the International Residential Code. Pitch also changes how much roof there is: a steeper roof has more surface over the same floor plan, which is why materials calculators ask for it.

Fig. 1 · A level held flat against the roof, with the rise measured 12″ from the contact point.

Method 1: Level and tape

This is the standard method and needs only a level and a tape measure. Work from a ladder at the rake (the sloped gable edge) so you can reach the roof surface without standing on it.

  1. Rest one end of a 24″ level on the roof surface and hold it perfectly level, bubble centred.
  2. Measure 12″ along the level from the end touching the roof and mark it.
  3. Measure straight down from the 12″ mark to the roof surface. That distance in inches is the rise.
  4. Write it as rise over 12. A 6″ reading is a 6/12 pitch.

Enter your numbers below to get the angle, slope and rafter multiplier.

Try it · Roof Pitch Calculator

Full calculator 
Pitch
6/12
Angle
26.57°
Slope
50.0%
Rafter ×
1.118

If your level is too short to mark 12″, measure over 6″ instead and double the reading. The ratio is what matters, so the calculator accepts any run.

Method 2: From the attic

Inside the attic you can take the same reading against a rafter and stay off the roof entirely.

  1. Hold the level horizontally with one end touching the underside of a rafter.
  2. Mark 12″ along the level from that point.
  3. Measure straight up from the mark to the bottom edge of the rafter.

The result is the same as on the roof surface, because the rafter and the roof deck run parallel. Choose a straight rafter away from any sag or repairs.

Method 3: Phone app

Inclinometer and level apps read the angle when you lay the phone on a rafter in the attic, or on a straight board resting on the roof. The app gives degrees; switch the Roof Pitch Calculator to the Angle tab to convert degrees into pitch. Phone sensors are less precise than a level and tape, so check the reading in two or three places.

Safety

We recommend staying off any roof steeper than about 7/12 unless you use a harness and anchor, and never walking on a wet, icy, mossy or windy roof. For people working on residential construction, OSHA requires fall protection when working 6 feet or more above a lower level. Both the ladder method and the attic method let you measure without walking the roof.

  • Set the ladder on firm, level ground and extend it at least 3 ft above the roof edge.
  • Keep three points of contact while you measure.
  • In the attic, step only on joists or boards laid across them, never on the ceiling drywall between them.