EstimatorKitFree roof pitch calculator
Roof pitch calculator — measure the roof you have
Four ways to pin down the pitch of a roof that already exists: a level and a tape, a phone’s inclinometer in degrees, or a rafter measured against either the run it covers or the height it climbs. Each returns the same four things — rise in 12, the angle to two decimals, the grade as a percent, and the multiplier that turns an area measured on the ground into the surface a roofer bids. Add the footprint and it converts that into whole roofing squares, and it tells you where the reading falls against the 2:12 floor for asphalt shingles and the 4:12 line above which the roof counts as steep for anyone working on it.
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- No signup
- Four ways to measure
- Degrees, percent and X:12
- Squares from a footprint
Hold a level against the roof or a rafter, then measure down from its far end.
Fractions are welcome: 5 3/8 is a valid drop. A longer level averages out the cupping in old sheathing, and the run field keeps the arithmetic honest so you never halve a 24 in reading in your head.
The area you would measure standing on the ground, gutter line to gutter line. Leave it empty and you still get the multiplier.
This roof reads as
6:12
Sitting on 6:12, which is a pitch roofs are framed and sold in.
- Angle
- 26.57°
- Grade
- 50%
- Footprint multiplier
- 1.118
What this reading rules in and out
Comfortably inside the range asphalt shingles are written for — IRC R905.2.2 — asphalt shingles are permitted only on slopes of 2:12 or steeper, and the doubled underlayment stops at 4:12.
For anyone working on it, this counts as a steep roof: 29 CFR 1926.500(b) — a roof steeper than 4:12 is a steep roof, and 1926.501(b)(11) requires fall protection on one at 6 ft.
How to measure the pitch of an existing roof
Two minutes with a level, and one decision about what to round.
Find a straight surface the roof actually follows
From inside, the underside of a rafter is the honest one: it is dead straight, it is dry, and nothing has been layered onto it. From outside, the rake board on a gable end works, and so does the roof surface itself as long as you bridge across at least two courses of shingle rather than resting on one. Old sheathing between rafters dishes by a quarter inch or more, and a short level laid in that dish reports a flatter roof than the framing underneath it.
Level the tool, then measure straight down from its far end
Hold the level against the surface, bring the bubble to center, and measure the vertical drop from the far end of the level down to the roof. Enter both the drop and the length of the level rather than converting: a 24 in level reading 11 in is a 5 1/2:12 roof, and halving readings in your head at the top of a ladder is where the mistake gets made. Fractions go in as fractions, so 5 3/8 needs no decimal.
Round to a pitch that gets framed, then keep the exact one
Roofs are built, ordered and quoted in half-pitch steps, so a reading of 5.83:12 is a 6:12 that has settled or been measured through a slightly cupped board. Use the rounded pitch when you talk to a supplier or a framer, and the exact reading when you multiply a footprint into an area — snapping first and multiplying second can move a 2,000 square foot roof by 18 square feet, which is a fifth of a square.
Technical specifications
| Measuring methods | Rise over a run of any length, an inclinometer angle in degrees, or a rafter length against either its level run or its total rise |
|---|---|
| Level presets | 12, 24 and 48 in, with any other length typeable; the drop accepts fractions such as 5 3/8 |
| Angle range | 0 to 89.99 degrees, reported to two decimals — 45.00 degrees is exactly 12:12 |
| Rounding | Snapped to the nearest half pitch, the increments roofs are actually framed and quoted in |
| Footprint multiplier | 1.0541 at 4:12, 1.1180 at 6:12 and 1.2019 at 8:12 |
| Squares from a footprint | A 1,450 sq ft footprint at 6:12 is 1,621 sq ft of roof, or 16.21 squares |
| Limits reported | IRC R905.2.2 at 2:12, R905.2.7 at 4:12, and the steep-roof definition in 29 CFR 1926.500(b) |
| Data kept | Nothing is stored — the reading disappears when the tab reloads |
Frequently asked questions
Is roof pitch the same thing as roof slope?
Not historically, though almost everyone now uses them interchangeably. Slope is rise over run and is written as X-in-12; pitch, in its older sense, is rise over the whole span, so a 6-in-12 slope is a one-quarter pitch. The X:12 convention won because it survives contact with a framing square, and this page uses it throughout — but the old meaning still turns up in books, in truss drawings and in the occasional inspector's vocabulary, and it is the reason a 'quarter pitch' roof is not a 3:12.
How accurate is a phone inclinometer on a roof?
Good to about half a degree if the phone is flat against something straight, which is roughly a tenth of an inch of rise per foot. The errors are almost never in the sensor: a case with a raised camera bump tilts the phone, shingle butts step the surface, and holding the phone in your hand instead of resting it adds a degree in either direction. Rest the long edge on a rafter or a rake board, take three readings, and use the middle one.
Can I get the pitch from a photograph or from satellite imagery?
Only roughly, and only from a true side elevation. A photograph taken from the ground looks up at the roof and foreshortens the run, which reads steeper than the roof is; aerial imagery does the opposite on the far slope. Both are useful for deciding whether a roof is nearer 4:12 or 9:12 before you drive out, and neither is good enough to order material from. Measure it against something physical before anything gets cut or delivered.
The two ends of my roof measure different pitches. Which do I use?
Measure a third and a fourth spot before deciding, because two different readings usually mean the ridge has sagged or one wall has settled rather than that the roof was framed on a taper. If the difference is under a quarter inch of rise per foot it is measurement noise from cupped sheathing and the steeper of the two is normally the original. If it is bigger than that, the roof is genuinely out of plane, and the material figure should use the larger area while the framing figure needs a look at the structure.
Does a steeper pitch mean a bigger waste factor?
No, and this is worth being clear about because plenty of estimates treat it as if it did. Pitch changes the area, through the multiplier, and it changes how the work is staged and priced. What drives cutting waste is the shape: rakes, hips, valleys, dormers and skylights all create cut edges, and a cut-up 4:12 roof wastes far more material than a plain 10:12 gable. Apply the multiplier here, then choose the waste allowance from the roof's outline, not from its steepness.
What pitch is 30 degrees?
6.93 in of rise per foot of run, so it gets framed as a 7:12. Degrees and pitch are related by a tangent rather than by a straight line, which is why the conversion has no shortcut: 45 degrees is exactly 12:12, but half of 45 degrees is not 6:12, it is 4.97:12. Anyone converting between the two often enough to notice usually ends up printing a table instead.
My roof measures 2:12. Can it still be shingled?
Yes, with a doubled underlayment — IRC R905.2.2 permits asphalt shingles down to 2:12, and R905.2.7 requires the second layer anywhere below 4:12. What tends to go wrong is not the code but the warranty: several manufacturers ask for a self-adhered membrane rather than felt over the whole deck at that slope, and installing to the code minimum without reading the wrapper is how a roof loses its coverage. Below 2:12 the shingle route closes entirely and the roof becomes a membrane job.
About measuring the pitch of a roof
Pitch is the one roof dimension you cannot take off a plan when the plan does not exist, and it decides three separate things at once: what covering the roof is allowed to carry, how much surface there is above a given footprint, and how the work has to be staged. Those three consequences do not scale together. A 2:12 and a 4:12 look nearly identical from the driveway and differ by 4 percent in area, yet one of them is at the outer edge of what asphalt shingles are written for and the other is comfortably inside it. Meanwhile a 12:12 adds 41 percent to the area and turns the job into scaffold work.
Where the measurement goes wrong is nearly always the surface, not the arithmetic. A level laid on shingle butts rides the step between courses; sheathing between rafters dishes over decades; a rafter length that includes the tail, paired with a run that stops at the wall, reports a roof steeper than the one you are standing on. Each way in has a different failure: the level method needs a straight surface, the inclinometer needs the phone resting rather than held, and the two rafter methods need both measurements taken between the same pair of points. When two of them agree, you have your pitch.
The output worth carrying away is the slope factor. It is the square root of one plus the pitch squared, and it converts a footprint you can measure with a tape on the ground into an area you would otherwise have to walk. The full set of factors for every pitch is laid out on the roof pitch chart, which prints. Once the pitch is settled, the roof area calculator handles a roof with more than one plane, the shingle calculator turns squares into bundles, and the siding calculator picks up the gable triangles the roof leaves behind. If you are framing rather than covering, the pitch feeds straight into the rafter length calculator and the rafter calculator.
The reading stays on the phone that took it
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.
The inclinometer figure is one you read off your own phone and type in — this page does not ask the browser for motion or orientation permissions, and there is no sensor access to grant or refuse.