Roof pitch chart: angle, percent and multiplier

Roof pitch chart

The multiplier converts flat measurements into sloped ones: roof area = footprint × multiplier, and rafter length = horizontal run × multiplier. For a 6/12 roof both are 11.8 % larger than the plan view.

How to calculate roof pitch

1. Measure the rise: the vertical height from the top of the wall plate to the ridge (or measure 12 in along a level and the drop to the roof).
2. Measure the run: the horizontal distance from the outside of the wall to the centre of the ridge — half the building width on a symmetrical gable.
3. Divide rise by run and multiply by 12. A 5 ft rise over a 12 ft run is 5 ÷ 12 × 12 = 5/12.
4. Or enter rise and run in the roof pitch calculator to get pitch, angle and percent at once.

From inside an attic, hold a level against the bottom of a rafter, mark 12 in on the level and measure straight up to the rafter — that number is the pitch.

Standard roof pitches and what they are used for

• Flat to 2/12 (up to 9.5°): low-slope roofs — membranes like TPO, EPDM or modified bitumen; shingles are not allowed below 2/12.
• 2/12 to 4/12: low pitch — shingles need a double underlayment; metal panels work well.
• 4/12 to 9/12 (18–37°): conventional pitch — most American houses; easy to walk on up to about 6/12.
• 9/12 to 12/12 (37–45°): steep — needs roof jacks and harnesses; sheds snow well; common on Tudor, Cape Cod and colonial houses.
• Above 12/12: very steep — A-frames and mansards; labor costs rise sharply.

Minimum pitch by roofing material

Roof pitch in degrees and percent

Builders in the US talk in x/12, engineers in degrees, and road and drainage plans in percent. Percent grade is simply rise ÷ run × 100: a 6/12 roof is 50 %, a 12/12 roof 100 % (45°). Remember that percent and degrees are not proportional — doubling the percent does not double the angle. The slope calculator converts any of them.

Common pitches by house style

Pitch, slope and angle: what is the difference?

In everyday use pitch and slope both mean rise per 12 in of run (6/12). Strictly, some carpentry books define pitch as rise over the full span, so a 6/12 slope would be a 1/4 pitch — you may still see that on old plans. Angle is the same steepness in degrees, which is how roofs are specified in Europe (a German or French roof of 30° is a 6.9/12 roof). The chart above converts between all three.

Climate and safety

• Snow country favors steeper roofs (8/12 and up) that shed snow; low slopes must be designed for the snow load.
• Hurricane zones often use 4/12 to 6/12 hip roofs, which handle wind uplift better than tall gables.
• Up to about 6/12 a roof is walkable with care; from 7/12 roofers use roof jacks, toe boards and fall protection, which raises labor cost.
• Very low slopes need extra underlayment or a membrane because water drains slowly and wind can push it under shingles.

How to find the pitch without climbing on the roof

1. From the attic: measure the vertical distance from the top of the ceiling joists to the underside of the ridge (the rise) and the horizontal distance from the outside of the wall to the ridge (the run).
2. From the gable end outside: measure the total height of the gable triangle and the width of the house; the run is half the width.
3. With a phone: many level apps measure an angle when you hold the phone against the roof edge or a rafter tail — convert the degrees with the roof pitch calculator.
4. From the plans: elevations usually mark the pitch with a small triangle, such as 6 over 12.

Pitch also decides attic space: a 4/12 roof over a 30 ft wide house rises only 5 ft at the ridge, while a 12/12 roof rises 15 ft — enough for a room with a knee wall.

Using pitch to estimate roofing

To estimate shingles, multiply the footprint including overhangs by the multiplier. A 40 × 30 ft house with 1 ft overhangs is 42 × 32 = 1,344 ft² in plan; at 6/12 the roof is 1,344 × 1.118 = 1,503 ft² before waste. With 10 % waste that is 16.53 squares, or 50 bundles of shingles — the roofing calculator does this in one step.

Rafters follow the same rule. For a 24 ft span at 6/12 with a 1½ in ridge board the run is 11 ft 11¼ in and each rafter is 13 ft 4 1/8 in to the ridge, 14 ft 5 5/8 in with a 12 in overhang. The rafter length calculator also gives the plumb and seat cut angles.