# My Roof Pitch

> Free roofing and construction calculators. Every tool shows the formula, the
> substituted numbers and the result, in imperial or metric units.

Results are planning estimates, not stamped engineering. Code-sensitive outputs
(snow load, minimum pitch, drainage) follow published ASCE 7, IRC and IPC methods.

## Key facts

- Roof pitch = (rise / run) x 12, written as X:12.
- Roof angle in degrees = arctan(rise / run).
- 4:12 = 18.43 degrees = 33.3% slope; 6:12 = 26.57 degrees = 50%; 12:12 = 45 degrees = 100%.
- Pitch multiplier = sqrt(rise^2 + run^2) / run; multiply footprint area by it for sloped area.
- Hip/valley factor = sqrt(rise^2 + 2*run^2) / run.
- Asphalt shingle minimum pitch: 2:12 with double underlayment, 4:12 standard (2021 IRC R905.2.2).

## Reference pages

- [Roof pitch chart](/roof-pitch-chart): every pitch from 1/4:12 to 24:12 in degrees, percent, multiplier and hip/valley factor.
- [Methodology](/methodology): every formula, rounding rule and code reference used sitewide.
- [About](/about): who builds and reviews these calculators.

## Guides

- [How to Calculate Roof Pitch: 6 Methods That Actually Work](/blog/how-to-calculate-roof-pitch): To calculate roof pitch, measure the vertical rise over exactly 12 inches of horizontal run and write the answer as X:12. A 1-foot level held against the rafter with a tape at the far end gives the rise directly. Pitch in degrees equals arctan(rise divided by run).
- [Roof Pitch to Degrees: Full Conversion Chart and Formula](/blog/roof-pitch-to-degrees-chart): Roof pitch converts to degrees with the arctangent function: angle equals arctan of rise divided by run. A 4:12 roof is 18.43 degrees, 6:12 is 26.57 degrees and 12:12 is exactly 45 degrees. To reverse it, multiply the tangent of the angle by twelve.
- [Common Roof Pitches Explained: 3:12 Through 12:12](/blog/common-roof-pitches-explained): The most common residential roof pitches run from 4:12 to 9:12, with 6:12 the single most used slope in North America. Below 4:12 a roof is low slope and needs sealed underlayment; above 8:12 it is not walkable and labour costs rise sharply.
- [Roof Pitch Multiplier: Chart, Formula and How to Use It](/blog/roof-pitch-multiplier-explained): A roof pitch multiplier converts flat footprint area into true sloped roof area. It equals the square root of rise squared plus run squared, divided by run. For a 6:12 roof the multiplier is 1.118, so 2,000 square feet of footprint carries 2,236 square feet of roof.
- [Minimum Roof Pitch by Material: IRC Limits for Every Covering](/blog/minimum-roof-pitch-by-material): Asphalt shingles require 2:12 minimum with double underlayment and 4:12 for standard installation. Standing seam metal goes to 1/4:12, exposed-fastener metal to 3:12, clay and concrete tile to 2.5:12, and single-ply membrane to 1/4:12 under the 2021 IRC.
- [Roofing Squares and Shingle Bundles: How Many You Need](/blog/roof-shingles-and-squares-guide): One roofing square is 100 square feet of roof surface, and standard shingles come three bundles to the square. Divide the pitch-adjusted roof area by 100 to get squares, add 10 to 15 percent waste, then multiply by three for bundles.
- [Shed and Lean-To Roof Pitch: How to Choose and Calculate It](/blog/shed-roof-pitch-guide): A shed roof is a single sloping plane, so its pitch equals the difference between the tall and short wall heights divided by the building depth, times twelve. Most sheds use 2:12 to 4:12; anything under 2:12 needs a membrane or standing seam covering.
- [Metal Roof Pitch: Minimums, Panel Lengths and Cost by Slope](/blog/metal-roof-pitch-guide): Mechanically seamed standing seam metal roofing works down to 1/4:12, snap-lock standing seam and exposed-fastener panels need 3:12, and metal shingles need 3:12. Panel length equals the run times the pitch multiplier plus overhang, ordered as one continuous piece where possible.
- [Roof Replacement Cost: How Roofing Quotes Are Actually Built](/blog/roof-replacement-cost-guide): A typical US asphalt shingle replacement costs $450 to $750 per square installed, so a 20-square roof runs about $9,000 to $15,000 including one layer of tear-off. Metal, tile and slate cost two to four times more per square.

## Pitch & Slope

- [Roof Pitch Calculator](/roof-pitch-calculator): Free roof pitch calculator. Enter rise and run to get pitch as X:12, the angle in degrees, slope percentage and the pitch multiplier, with a live diagram.
  Answer: Roof pitch is the ratio of vertical rise to horizontal run, written as X:12. A 6:12 pitch rises 6 inches over 12 inches of run, equal to 26.57° or a 50% slope. Divide rise by run, then apply arctangent to get the angle in degrees.
  Formula: pitch = rise / run, expressed per 12 units of run
- [Roof Slope Calculator](/roof-slope-calculator): Calculate roof slope from rise and run. Get slope as a percentage, an angle in degrees and an X:12 ratio, with drainage guidance and a live diagram.
  Answer: Roof slope is rise divided by run, stated as a percentage. A roof rising 6 units over 12 units of run has a 50% slope, equal to 26.57° or a 6:12 pitch. Multiply rise ÷ run by 100 for percentage, or take the arctangent for degrees.
  Formula: slope % = (rise / run) × 100
- [Roof Pitch to Angle Converter](/roof-pitch-to-angle-converter): Convert roof pitch to degrees and back. Enter any X:12 pitch or any angle to get the exact conversion, slope percentage, multiplier and a full reference table.
  Answer: To convert roof pitch to degrees, divide the rise by 12 and take the arctangent. A 6:12 pitch is arctan(0.5) = 26.57°. To reverse it, take the tangent of the angle and multiply by 12: a 30° roof is a 6.93:12 pitch.
  Formula: angle = arctan(rise / 12) × (180 / pi)

## Area & Measurement

- [Roof Area Calculator](/roof-area-calculator): Calculate true sloped roof area from your building footprint and pitch. Get square feet, square metres, roofing squares and a waste-adjusted order quantity.
  Answer: Roof area equals the building footprint multiplied by the pitch multiplier. A 40 ft × 30 ft house with a 6:12 roof has a 1,200 sq ft footprint and a 1.1180 multiplier, giving 1,341.6 sq ft of actual roof surface — about 13.4 roofing squares.
  Formula: roof area = footprint length × footprint width × pitch multiplier
- [Roof Square Footage Calculator](/roof-square-footage-calculator): Work out roof square footage from ridge length, rafter length and pitch. Converts to roofing squares, square metres and a bundle count for shingles.
  Answer: Roof square footage is the ridge length multiplied by the rafter length, doubled for a two-plane gable. A 40 ft ridge with 18 ft rafters gives 40 × 18 × 2 = 1,440 sq ft, which is 14.4 roofing squares before any waste allowance.
  Formula: plane area = ridge length × rafter length
- [Sloped Roof Area Calculator](/sloped-roof-area-calculator): Convert building footprint area to true sloped roof area using the pitch multiplier. Get roofing squares, square metres, and a waste-adjusted order quantity.
  Answer: Sloped roof area is the footprint area multiplied by the pitch multiplier. A 1,500 sq ft footprint with a 6:12 roof has a 1.1180 multiplier, giving 1,677 sq ft of actual roof surface — about 16.8 roofing squares.
  Formula: sloped area = footprint area × pitch multiplier

## Framing & Structure

- [Rafter Length Calculator](/rafter-length-calculator): Calculate common rafter length from span and pitch. Get the line length, overall length with overhang, plumb and seat cut angles, and a span reference table.
  Answer: Rafter length is the hypotenuse of the rise and run triangle: √(rise² + run²). For a 24 ft span at 6:12, the run is 12 ft, rise is 6 ft, and the line length is 13.42 ft. Add the overhang along the same slope to get the cut length.
  Formula: line length = sqrt(run^2 + rise^2)
- [Rafter Angle Calculator](/rafter-angle-calculator): Calculate rafter cut angles, birdsmouth size and speed square settings from span and pitch. Get plumb cut, seat cut, rafter length and a cut diagram.
  Answer: For a symmetrical gable, the plumb cut angle is 90° minus the roof angle, and the seat cut equals the roof angle. A 6:12 roof sits at 26.57°, so the plumb cut is 63.43° and the seat cut is 26.57°. Set a speed square to the pitch number — 6 on the Common scale — for the same layout.
  Formula: angle = arctan(pitch / 12)
- [Roof Truss Calculator](/roof-truss-calculator): Calculate how many roof trusses you need, plus peak height, top chord length and bottom chord length from your span, pitch and spacing.
  Answer: Truss count is the building length divided by the spacing, plus one. A 40 ft building at 24 in centres needs 21 trusses. Peak height is half the span times the pitch ratio, and each top chord equals half the span times the pitch multiplier.
  Formula: count = floor(building length / spacing) + 1
- [Purlin Calculator](/purlin-calculator): Work out purlin spacing, total linear feet and number of purlins for a metal roof. Includes span, pitch, overhang and common spacing presets.
  Answer: Purlin count is the roof slope length divided by the purlin spacing, plus one. A 40 ft long gable roof slope at 24 in centres needs 21 purlins per side, or 42 total. Total purlin length equals count times the rafter or truss top-chord length.
  Formula: purlin length = (span / 2 + overhang) × sqrt(rise^2 + 144) / 12
- [Hip Rafter Calculator](/hip-rafter-calculator): Calculate hip rafter length, plumb and side cut angles, and the number of jack rafters for a hip roof from span, pitch and overhang.
  Answer: A hip rafter runs at a 45° plan angle, so its run per foot is 16.97 inches instead of 12. For a 24 ft square building at 6:12 with 2 ft overhangs, the hip run is 15.56 ft and the hip length is 17.42 ft. Jack rafters shorten by the common rafter spacing divided by 1.414 each step.
  Formula: hip run = (span / 2 + overhang) × sqrt(2)

## Materials & Quantities

- [Roof Shingle Calculator](/roof-shingle-calculator): Work out how many shingle bundles and squares your roof needs. Includes waste allowance, starter strip, ridge cap and nail quantities for asphalt shingles.
  Answer: Shingle quantity is roof area divided by 100 to get squares, plus waste, times three bundles per square. A 2,000 sq ft roof with 10% waste needs 22 squares, which is 66 bundles of standard three-tab or architectural shingles.
  Formula: squares = (footprint × pitch multiplier / 100) × (1 + waste)
- [Metal Roof Calculator](/metal-roof-calculator): Calculate metal roofing panels, panel length, screws and trim from your roof dimensions and pitch. Works for standing seam and exposed-fastener panels.
  Answer: Panel count is the eave length divided by the panel's net coverage width, rounded up. Panel length is the run times the pitch multiplier plus the overhang. A 40 ft eave with 36 in panels needs 14 panels per slope, at roughly 80 screws each.
  Formula: panels = ceil(eave length / net coverage width)
- [Roof Tile Calculator](/roof-tile-calculator): Calculate how many roof tiles, bundles and underlayment rolls you need for clay, concrete or Spanish tile roofs from footprint, pitch and waste.
  Answer: Tile quantity is sloped roof area divided by the tile coverage per piece, plus waste. A 2,000 sq ft roof covered with 13×16 inch tiles at a 1.6 ft² exposure needs about 1,470 tiles before waste.
  Formula: sloped area = footprint × pitch multiplier
- [Underlayment Calculator](/underlayment-calculator): Calculate how many rolls of roofing underlayment you need for any roof area. Supports #15 felt, synthetic and ice-and-water shield coverage widths.
  Answer: Underlayment rolls are roof area divided by the roll coverage. A 2,000 sq ft roof needs 2 rolls of synthetic underlayment at 1,000 sq ft per roll, or 5 rolls of #15 felt at 432 sq ft per roll.
  Formula: net = roll length × (roll width − overlap)
- [Roofing Nails Calculator](/roofing-nails-calculator): Estimate roofing nails or screws by weight and count for shingles, metal panels and underlayment. Supports 4-nail and 6-nail patterns.
  Answer: A standard four-nail pattern uses about 320 nails per square, or just over 2 pounds. A six-nail high-wind pattern uses about 480 nails per square, or roughly 3 pounds. For a 20-square roof that is 6,400 to 9,600 nails.
  Formula: nails = (roof area / 100) × pattern × 80
- [Roof Sheathing Calculator](/roof-sheathing-calculator): Calculate how many plywood or OSB roof sheathing sheets you need from roof area, sheet size and waste. Supports 4×8 and metric panels.
  Answer: Sheathing sheets are sloped roof area divided by the net sheet area, plus waste. A 2,000 sq ft roof needs about 70 sheets of 4×8 plywood at 32 sq ft per sheet with 5% waste.
  Formula: net area = sheet width × sheet length

## Cost & Estimating

- [Roof Cost Calculator](/roof-cost-calculator): Estimate what a new roof costs. Enter your footprint, pitch and material rate to get material, labour, tear-off and disposal costs broken out per square.
  Answer: Roof cost is the sloped area in squares multiplied by the combined material and labour rate per square, plus tear-off and disposal. At $450 per square installed, a 20-square roof costs about $9,000 before tear-off, which adds $100 to $150 per square.
  Formula: total = squares × (material rate × (1 + waste) + labour rate × labour factor + tear-off rate) + extras

## Load, Drainage & Performance

- [Snow Load Calculator](/snow-load-calculator): Calculate flat and sloped roof snow load from ground snow load using the ASCE 7 method, including exposure, thermal and importance factors and total roof load.
  Answer: Flat roof snow load is pf = 0.7 × Ce × Ct × Is × pg. With a 40 psf ground load, standard exposure and a heated building, pf is 28 psf. Multiply by the slope factor Cs to get the sloped roof load, which drops as pitch increases.
  Formula: pf = 0.7 × Ce × Ct × Is × pg
- [Gutter Slope Calculator](/gutter-slope-calculator): Calculate the correct gutter slope and total drop over any run. Get fall per foot, downspout count and the high and low end heights for a level line.
  Answer: Gutters should fall about 1/4 inch every 10 feet toward the downspout. Over a 40 foot run that is a 1 inch total drop. Runs longer than 40 feet should slope from a high point in the middle toward a downspout at each end.
  Formula: total drop = (run length / 10) × fall per 10 ft
- [Gutter Size Calculator](/gutter-size-calculator): Size gutters and downspouts from roof area, pitch and local rainfall intensity. Get recommended gutter profile, downspout count and capacity check.
  Answer: Gutter size is driven by the peak flow rate, which is roof area times rainfall intensity times 0.623 divided by 60. A 2,000 sq ft roof in a 4 in/hr storm produces about 83 gallons per minute. A 5-inch K-style gutter with two downspouts can handle that; a half-round system of the same size cannot.
  Formula: gpm = roof area × rainfall intensity × 0.623 / 60 × pitch factor
- [Ridge Vent Calculator](/ridge-vent-calculator): Calculate ridge vent length and net free vent area for balanced attic ventilation. Matches intake vent area and gives code-compliant NFVA guidance.
  Answer: A balanced attic needs 1 square foot of net free vent area for every 150 square feet of attic floor. Half of that should be low intake and half high exhaust. A 2,000 sq ft attic needs 13.3 sq ft NFVA total, so 6.7 sq ft of ridge vent and 6.7 sq ft of soffit vent.
  Formula: total NFVA = attic area / ventilation ratio

## Machine-readable index

- [JSON API](/api/public/calculators.json)
- [Sitemap](/sitemap.xml)