Roof Pitch Calculator
Convert between roof pitch, angle in degrees and slope multiplier, then turn your building footprint into real roof surface area, rafter length, roofing squares and shingle bundles. Works from a rise and run measurement, a phone level reading, or a pitch you already know.
- ✓ Pitch, degrees & multiplier
- ✓ Rafter length included
- ✓ Squares & bundles
- ✓ Live pitch diagram
- ✓ Imperial & metric
Your roof
Common pitches
Roof size & materials
Area assumes a simple gable or hip roof over a rectangular footprint. Dormers, valleys, turrets and multiple wings all add surface and waste, so treat the result as a solid starting estimate rather than a final order.
Pitch, angle and multiplier are three views of one number
Roofers speak in rise over run, building control wants degrees, and material take-offs need the slope multiplier. They all come from the same right-angled triangle, which is why converting between them is arithmetic rather than guesswork.
pitch = (rise ÷ run) × 12angle = arctan(rise ÷ run)multiplier = √((pitch ÷ 12)² + 1)roof area = footprint × multiplierrafter = run × multipliersquares = roof area ÷ 100Worked example: a 40 by 28 ft house with 1 ft eaves has a 42 by 30 ft footprint, which is 1,260 sq ft. At a 6:12 pitch the multiplier is 1.118, so the real roof surface is 1,409 sq ft — almost 150 sq ft more than the plan view suggests. Order from the footprint and you finish a square and a half short.
Why this beats a plain pitch converter
Starts from whatever you have
A pitch you were told, a rise and run you measured with a level, or a degree reading off a phone inclinometer. All three routes land on the same result set.
Rafters and ridge height
Common rafter length and the height of the ridge above the wall plate come out with the pitch, so you can price timber at the same time.
Footprint to real surface
Enter the building and the eave overhang and get the sloped area, not the plan area. This is the step most people skip and most shortfalls come from.
Squares and bundles
Converted to roofing squares, then to bundles at your own bundles-per-square, with waste and a running cost.
Tells you what the pitch means
Low slope, walkable or steep changes the underlayment, the shingle warranty and whether the job needs fall protection. The classification is shown with the number.
Live diagram
The triangle is drawn to scale as you type, which makes a mistyped rise obvious immediately.
How to measure and use roof pitch
- Measure the rise over 12 inches of run
Hold a level horizontally against a rafter or the gable barge board, mark 12 inches along it, then measure straight down to the roof surface. That drop in inches is your pitch.
- Or read the angle
A phone inclinometer laid on a rafter in the loft gives degrees directly. Switch the calculator to angle mode and it converts back to rise in 12.
- Enter the building footprint
Length and width of the outside walls, plus the eave overhang. The calculator adds the overhang on all four sides before applying the multiplier.
- Read the materials
Squares, bundles and cost update live. Raise the waste allowance for cut-up roofs with valleys, dormers or hips, where 15% is more realistic than 10%.
Roof pitch to angle chart
Every common pitch with its angle in degrees, its slope multiplier and what it means for the build.
| Pitch | Angle | Multiplier | Classification |
|---|---|---|---|
| 1:12 | 4.76° | 1.0035 | Low slope — membrane roofing only |
| 2:12 | 9.46° | 1.0138 | Low slope — shingle minimum, double underlayment |
| 3:12 | 14.04° | 1.0308 | Low slope — double underlayment still required |
| 4:12 | 18.43° | 1.0541 | Conventional — standard shingle installation |
| 5:12 | 22.62° | 1.0833 | Conventional — walkable |
| 6:12 | 26.57° | 1.1180 | Conventional — the most common residential pitch |
| 7:12 | 30.26° | 1.1577 | Conventional — walkable with care |
| 8:12 | 33.69° | 1.2019 | Conventional — upper limit of comfortable walking |
| 9:12 | 36.87° | 1.2500 | Steep — roof jacks or harness needed |
| 10:12 | 39.81° | 1.3017 | Steep — fall protection required |
| 11:12 | 42.51° | 1.3566 | Steep |
| 12:12 | 45.00° | 1.4142 | Steep — exactly 45 degrees |
| 14:12 | 49.40° | 1.5366 | Very steep — specialist access |
| 16:12 | 53.13° | 1.6667 | Very steep — often a gable feature |
| 18:12 | 56.31° | 1.8028 | Very steep — A-frame territory |
| 24:12 | 63.43° | 2.2361 | Very steep — chalet and A-frame |
What the slope multiplier costs you if you ignore it
Extra roof surface over a 2,000 sq ft footprint, purely from pitch.
| Pitch | Roof surface | Extra area | Extra squares |
|---|---|---|---|
| 3:12 | 2,062 sq ft | +62 sq ft | +0.6 |
| 4:12 | 2,108 sq ft | +108 sq ft | +1.1 |
| 6:12 | 2,236 sq ft | +236 sq ft | +2.4 |
| 8:12 | 2,404 sq ft | +404 sq ft | +4.0 |
| 10:12 | 2,603 sq ft | +603 sq ft | +6.0 |
| 12:12 | 2,828 sq ft | +828 sq ft | +8.3 |
At a 12:12 pitch you are buying more than eight extra squares of material that never appear on a floor plan. That is the entire reason the multiplier exists.
Practical notes before you order
- ✓Below 2:12, shingles are out. Manufacturers void warranties on low slope; that roof wants a membrane system instead.
- ✓2:12 to 4:12 needs double underlayment. Water moves slowly on shallow slopes and wind can drive it back up under the courses.
- ✓Steeper roofs shed better. They clear snow and debris more readily and generally last longer for the same material.
- ✓Cut-up roofs waste more. Valleys, hips and dormers mean 15% is a safer allowance than the usual 10%.
- ✓Labour rises with pitch. Anything past 8:12 needs staging or harnesses, and quotes climb accordingly.
- ✓Measure from the ground where you can. A gable end, a loft rafter or a photo taken square-on all beat climbing a wet roof.
Roof pitch FAQs
How do I calculate roof pitch?
Hold a spirit level horizontally against the underside of a rafter or along the gable end, measure 12 inches along the level from where it touches the roof, then measure vertically from that 12 inch mark up to the roof surface. If the drop is 6 inches you have a 6:12 pitch. Expressed as a formula, pitch equals rise divided by run, times 12.
What is a 6/12 roof pitch in degrees?
26.57 degrees. The slope multiplier is 1.118, meaning the actual roof surface is 11.8 percent larger than the footprint it covers. 6:12 is the most common residential pitch in much of the world because it sheds water well and is still safe to walk.
What is a roof pitch multiplier?
A single number that converts flat plan area into sloped roof area. It is the square root of the pitch over 12 squared, plus one. For a 4:12 roof it is 1.0541 and for a 12:12 roof it is 1.4142, so a 45 degree roof has 41 percent more surface than the ground it covers.
What is the most common roof pitch?
Most residential roofs fall between 4:12 and 9:12, with 6:12 the single most common. Anything from 4:12 to 8:12 is considered conventional and walkable, which keeps installation straightforward and labour costs down.
What is the minimum roof pitch for asphalt shingles?
2:12 is the usual manufacturer minimum, and between 2:12 and 4:12 a double layer of underlayment is normally required for the warranty to stand. Below 2:12 shingles should not be used at all; that roof needs a membrane system such as EPDM, TPO or torch-on felt.
How do I calculate roof area from the house square footage?
Multiply the footprint, including the eave overhang on all sides, by the slope multiplier for your pitch. A 1,260 sq ft footprint at 6:12 gives 1,260 times 1.118, which is 1,409 sq ft of roof. Add your waste allowance after that, then divide by 100 to get roofing squares.
How many bundles of shingles are in a square?
Three for most standard three-tab and architectural shingles, where a square covers 100 sq ft of finished roof. Heavier designer and luxury shingles can run four or even five bundles per square, so check the wrapper rather than assuming, and change the bundles-per-square field to match.
How do I measure roof pitch without getting on the roof?
Three safe options. Measure the gable end from a ladder with a level and tape. Go into the loft and measure the rise over 12 inches along the underside of a rafter. Or lay a phone with an inclinometer app flat on a rafter and read the angle directly, then use the angle mode here to convert it back to pitch.
Get the pitch and the material list in one go
Enter a pitch, a measurement or an angle, add your footprint, and walk away with rafter lengths, squares, bundles and a cost.
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