Roofing
Roof pitch calculator
6:12, 26.6 degrees, a 50 per cent grade and a factor of 1.118 are the same roof said four ways. This translates between them — and works the pitch out from a spirit level if you do not know it.
Written and edited by Pablo Ruiz Quintero
Last reviewed 2026-09-16 · Nothing you type leaves your browser
What do you already know?
Everyone states a pitch differently. Put in whichever form you have and read the others off.
How far it climbs.
Over how far. Roofers always say 12.
The plan area under the roof. Leave it if you only want the conversion.
That pitch is
6:12
26.6° · 50% grade · ×1.118 on area
As roofers say it
6:12
Inches of rise for every 12 inches of horizontal run. The only form that appears on a shingle wrapper.
As an angle
26.6°
What a drawing, a protractor or a phone app will tell you.
As a grade
50%
How panel and membrane manufacturers state a minimum slope.
Area multiplier
×1.118
Footprint × this = roof area. It is √(rise² + 144) ÷ 12 — Pythagoras, not a lookup table.
1,200 ft² of house is 1,342 ft² of roof
142 ft² more than the plan shows — 11.8%. That is the gap between quoting from a floor plan and quoting from a roof, and it is the commonest reason a material order comes up short. Turn it into shingles or into metal panels.
What this pitch allows
- Walking on it
Comfortable for most roofers in decent boots.Yes - Asphalt shingles
Allowed with standard underlayment.Yes - Metal panels that reach this low
- Corrugated, exposed fastener
- Ribbed / R-panel, exposed fastener
- Standing seam, snap-lock
- Standing seam, mechanically seamed
Worth knowing
- A 6:12 pitch is 26.6°, a 50% grade, and multiplies the footprint by 1.118. All four are the same fact said four ways — the multiplier is √(rise² + 144) ÷ 12, which is Pythagoras rather than a table.
- Over 1,200 ft² of footprint that is 1,342 ft² of roof — 142 ft² more than the plan shows. Quoting from the footprint is how a roof order comes up short, and the error grows with the pitch.
On this page — 7 sections
One roof, four numbers
The short version
- 6:12, 26.6°, 50% and ×1.118 are the same fact said four ways, for four different audiences.
- The multiplier is Pythagoras, not a table: √(rise² + 144) ÷ 12.
- A spirit level and a tape measure it. Drop ÷ level length × 12.
- The pitch decides what can go on it. Below 2:12, shingles are not allowed at all.
A roofer says 6:12. An architect says 26.6 degrees. A panel manufacturer says 50 per cent. A materials calculator wants 1.118. They are describing exactly the same roof, and most of the searching people do about roof pitch is not a design question — it is a translation problem.
All four come out of one right-angled triangle, so none of them is an approximation and none needs a lookup. The roof slope is the hypotenuse; the footprint is the base; the rise is the third side.
multiplier = √(rise² + 144) ÷ 12 · angle = atan(rise ÷ 12) · grade = rise ÷ 12
- rise
- inches of climb per 12 inches of run
- 144
- 12², the run squared — every form assumes a run of 12
- multiplier
- footprint × this = roof area, and run × this = rafter length
Worked through — A 6:12 roof: √(36 + 144) = √180 = 13.416, over 12 is 1.1180. The angle is atan(0.5) = 26.6°. The grade is 6 ÷ 12 = 50%. A 1,200 ft² footprint under it is 1,342 ft² of roof.
National Institute of Standards and Technology, NIST Special Publication 811, Guide for the Use of the International System of Units (2008 edition, current) · checked 2026-09-16
Measuring it with a level and a tape
There is a tool for this — a pitch gauge with a pivoting arm — and there is no need to own one. A spirit level and a tape do the same job.
Hold the level against the underside of a rafter, or against the roof surface. Bring the bubble to centre. Then measure straight down from the far end of the level to the surface. That drop, divided by the length of the level, times twelve, is the pitch.
A 24 inch level makes the arithmetic easy — a 12 inch drop is 6:12 — but any length works because it is a ratio. A longer level is more accurate, because it averages out the bumps.
Getting a reading you can trust
- Measure on a rafter inside the loft if you can. It is safer, and there is no covering thickness in the way.
- If you measure outside, sit the level on the shingle surface rather than bridging two courses.
- Keep the level truly horizontal — the bubble decides the reading, not the roof.
- Measure straight down at the far end, not at an angle along the roof.
- Take three readings along the same slope. A sagging rafter will give one odd one.
- Measure each slope separately where a roof has more than one pitch.
- Expect a round number. Roofs are built to whole twelfths, so 5.8:12 almost always means 6:12 and a measurement problem.
What the pitch does to the area
The multiplier is the reason this matters commercially. A floor plan gives a footprint; the roof is always larger, and how much larger climbs steeply with the pitch.
Roof surface as a multiple of the footprint it covers, by pitch.
×1.054
4:12
5% more than the footprint
×1.118
6:12
12% more — the commonest pitch
×1.250
9:12
25% more, and no longer walkable
×1.414
12:12
41% more — √2, the diagonal of a square
On a 1,200 square foot footprint that is the difference between 1,265 and 1,697 square feet of roof — over five squares of material on the same house. It is the commonest reason a roofing order comes up short, and it is entirely avoidable.
The roofing calculator takes the footprint and the pitch and gives bundles, underlayment, ridge and the tear-off — with this multiplier already applied.
Turn it into materialsWhat the pitch lets you put on it
Pitch is not only arithmetic. It decides what covering the roof can legally and sensibly take, because everything that laps rather than seals relies on gravity beating wind-driven rain.
| Pitch | Angle | Multiplier | What it means |
|---|---|---|---|
| 2:12 | 9.5° | ×1.014 | The absolute minimum the code allows shingles on, and only with a doubled underlayment. Below this it has to be a membrane roof. |
| 3:12 | 14.0° | ×1.031 | Still low slope: allowed, but the doubled underlayment requirement runs all the way to 4:12. |
| 4:12 | 18.4° | ×1.054 | Walkable, common on ranch houses and extensions. |
| 6:12 | 26.6° | ×1.118 | The most common residential pitch in the US. Adds 12% to the area. |
| 8:12 | 33.7° | ×1.202 | Not walkable. Labour rates rise from here and staging is needed. |
| 10:12 | 39.8° | ×1.302 | Adds 30% to the area over the footprint, before any waste. |
| 12:12 | 45.0° | ×1.414 | Adds 41%. Every square foot of house is 1.41 ft² of roof. |
International Code Council, International Residential Code, Section R905.2, Asphalt shingles · checked 2026-09-16
| Low pitch, under 4:12 | Steep, over 8:12 | |
|---|---|---|
| Shingles | Allowed to 2:12, with doubled underlayment | Fine, and they shed fast |
| Metal | Seamed standing seam only, to 1:12 | Anything |
| Walking it | Easy | Staging or a harness |
| Labour | Standard rate | Steep-pitch surcharge |
| Material quantity | Close to the footprint | A third more or worse |
| Risk | Water backing up under laps, ice dams | Falls, and wind uplift at the ridge |
Five ways this goes wrong
01Ordering material from the footprint
The roof is always bigger, by twelve per cent at 6:12 and forty-one at 12:12. On a 1,200 ft² house that is several squares of shingles.
Instead — Multiply the footprint by the pitch multiplier first. It is the single number this page exists to give you.
02Averaging two pitches
The multiplier is not linear, so the average of two multipliers is not the multiplier of the average. A roof with a 4:12 and a 10:12 slope is two calculations.
Instead — Measure and convert each slope separately, then add the areas.
03Trusting one measurement
A sagging rafter, a doubled shingle course or a level held a degree off all give a plausible wrong answer — and roofs are built to whole twelfths, so an odd reading is usually a measuring error.
Instead — Three readings along the same slope, and take the one that repeats.
04Putting shingles on a low slope
Below 4:12 wind drives rain back up under the laps, and below 2:12 the code does not allow it at all. It stays dry for years and fails in one storm.
Instead — Doubled underlayment between 2:12 and 4:12, and a membrane or seamed metal below that.
05Pricing a steep roof over the phone
Past about 7:12 the work changes: staging, jacks, harnesses, slower everything. A quote given without seeing it is a quote that will be revised.
Instead — Establish the pitch first — with a level, from the loft — and say it when you ask for a price.
How this converts
- 01Find a straight run of roof or rafterInside on a rafter is safer and usually more accurate than outside on the covering.
- 02Hold the level against it and bring the bubble centreOne end touching the surface, the level horizontal.
- 03Measure straight down at the far endFrom the underside of the level to the surface. On a 24 in level, 12 in of drop is a 6:12 pitch.
- 04Scale it to twelveDrop divided by level length, times 12. It is the same pitch however long the level is.
- 05Check it in two more placesA sagging rafter or a thick shingle course gives an odd number. The reading that repeats is the real one.
- 06Convert to whatever the next person needsDegrees for a drawing, percent for a panel spec, the multiplier for an area.
All four forms come from the same right-angled triangle, so the conversions are exact rather than tabulated: the multiplier is √(rise² + 144) ÷ 12, the angle is the arctangent of rise over 12, and the grade is rise over 12 as a percentage. The minimum slopes for shingles come from the residential code and those for metal panels from the metal construction association’s guidance. Everything is on the sources page, dated.
One assumption worth stating: everything here normalises to a run of 12 inches, because that is the form every code table, product spec and shingle wrapper uses. If you measure over a 24 inch level or a 4 foot straightedge the ratio is the same — the tool scales it for you, and it is worth measuring over the longest span you can.
Nothing you type is sent anywhere — the whole calculation runs in your browser.
The words on a roof drawing
Rise over run and the multiplier are the two that travel between trades. The rest is vocabulary.
- Rise over run
- Inches of vertical climb for every 12 inches of horizontal travel. Written 6:12 or 6/12, and it is the only form that appears on a shingle wrapper or in a code table.
- Pitch versus slope
- Used interchangeably in the trade. Strictly, slope is rise over run and pitch is rise over the full span — so a 6:12 slope is a 1/4 pitch — but almost nobody uses the strict sense any more.
- Area multiplier
- The number that turns a footprint into a roof area. It is the hypotenuse of a right triangle over its base: √(rise² + 144) ÷ 12.
- Percent grade
- Rise divided by run, as a percentage. A 6:12 roof is a 50 per cent grade. It is how panel and membrane manufacturers state a minimum slope, and how civil drawings state a fall.
- Low slope
- Anything below 4:12 for shingles, where the code requires the underlayment to be doubled, and below 2:12 where shingles are not permitted at all.
- Steep slope surcharge
- The extra a roofer charges past about 7:12, when the roof stops being walkable and staging, jacks or harnesses are needed. It is labour, not material.
- Rafter length multiplier
- The same number as the area multiplier, used differently: run in feet times the multiplier gives the rafter length along the slope.
- Span, run and rise
- Span is the full width the roof crosses; run is half of it on a symmetrical gable; rise is the height from the wall plate to the ridge.
- Pitch gauge
- A small tool with a pivoting arm that reads the pitch directly when held against a rafter. A spirit level and a tape do the same job with arithmetic.
- Ice dam
- Meltwater refreezing at a cold eave and backing up under the covering. It is far more likely on a low pitch, which is part of why low slopes need more underlayment.
- Membrane roof
- A fully sealed sheet — EPDM, TPO, modified bitumen — that does not rely on slope to shed water. It is what a roof below the shingle minimum has to be, unless it is seamed metal.
- Unequal pitches
- Two slopes of a roof that differ, common where an extension meets a house. Each slope has to be measured separately, because the multiplier is not an average.
Common questions
- What is a 6/12 roof pitch in degrees?
- 26.6 degrees. The conversion is the arctangent of the rise over the run: atan(6 ÷ 12) in degrees. It is also a 50 per cent grade, and it multiplies the footprint by 1.118 to give the roof area.
- How do you calculate roof pitch?
- Hold a spirit level against the rafter or the roof surface, level it, and measure straight down from the far end to the surface. Divide that drop by the length of the level and multiply by 12. A 12 inch drop on a 24 inch level is 6:12. Measuring on a rafter inside the loft is safer and usually more accurate than on the covering outside.
- What is the roof pitch multiplier?
- The number that converts a plan footprint into actual roof area: √(rise² + 144) ÷ 12. At 4:12 it is 1.054, at 6:12 1.118, at 12:12 1.414. It is geometry — the slope is the hypotenuse of a triangle whose base is the plan — rather than a figure from a table.
- What is the minimum roof pitch for shingles?
- 2:12, and between 2:12 and 4:12 the underlayment has to be doubled. Below 2:12 asphalt shingles are not permitted: it has to be a membrane, or a mechanically seamed standing seam, which is rated to 1:12 because the seam is folded shut rather than lapped.
- What roof pitch can you walk on?
- Up to about 6:12 is comfortable for most roofers in decent boots, 7:12 is the limit, and past that nobody walks it — staging, roof jacks or a harness. The point matters to a quote as much as to safety, because labour carries a steep-pitch surcharge from around 8:12 and a roofer will want to see it before pricing.
- Is pitch the same as slope?
- In practice yes, and everyone in the trade uses them interchangeably. Strictly, slope is rise over run — 6:12 — and pitch is rise over the whole span, so the same roof is a 1/4 pitch. The strict sense survives mainly in older texts, and every code table and product spec uses the rise-over-12 form.
- How do I convert degrees to roof pitch?
- Multiply the tangent of the angle by 12. A 30 degree roof is tan(30) × 12 = 6.93, so about 7:12. It rarely lands on a round number, which is why drawings give degrees and roofers give twelfths — they are describing the same roof for different purposes.
- What is a percent grade on a roof?
- Rise divided by run, expressed as a percentage: 6:12 is 50 per cent. Panel and membrane manufacturers state minimum slopes this way, and so do civil drawings. It is worth knowing because a spec saying 2 per cent minimum fall is not talking about roofs in twelfths at all.
- Does roof pitch change how much material I need?
- Substantially. A 1,200 ft² footprint is 1,265 ft² of roof at 4:12 and 1,697 at 12:12 — a difference of 432 square feet on the same house. Quoting from a floor plan instead of the roof is the commonest way an order comes up short.
- What pitch is a 45 degree roof?
- 12:12 — exactly one inch of rise for every inch of run. It multiplies the footprint by 1.414, which is √2, because at 45 degrees the slope is the diagonal of a square. Every square foot of house is nearly one and a half of roof.
- Can a roof have two different pitches?
- Often, and it is normal where an extension or a dormer meets the original house. Each slope has to be measured and converted separately — the multiplier is not something you can average, because it is not linear.
- Why is my measured pitch not a round number?
- Usually a sagging rafter, a thick course of shingles under the level, or a level that was not quite horizontal. Roofs are built to round pitches, so an odd reading is a measurement problem far more often than a design one. Measure in two or three places and take the value that repeats.
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About the author
Pablo Ruiz Quintero — Editor
Editor of MaterialsEstimator. Decides which documents count as a source, what every default value is, and where the line sits between what the reader parses and what the engines compute.
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