All roofing calculators
Twelve tools covering pitch, area, framing, materials, cost and load. Every result shows its working and links to the formula it came from.
Pitch & Slope
Pitch tools convert between the three ways a roof slope gets written down: the rise-over-run ratio used on US framing plans, the angle in degrees used almost everywhere else, and the percentage grade used in drainage design. Every tool here works from the same arctangent relationship, so results agree across the set.
- Roof Pitch CalculatorFree 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.
- Roof Slope CalculatorCalculate 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.
- Roof Pitch to Angle ConverterConvert 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.
- Degrees to Pitch CalculatorConvert a roof angle in degrees to an X:12 pitch, percent slope and area multiplier. Shows the nearest standard framing pitch and the tan formula used.
- Metric Roof Pitch CalculatorMetric roof pitch calculator for the UK, Australia, NZ and South Africa. Enter rise and run in mm or metres for degrees, 1:X ratio and rafter length.
Area & Measurement
A roof is always larger than the building underneath it. These tools apply the correct pitch multiplier to a measured footprint so you order materials for the real surface, not the plan view.
- Roof Area CalculatorCalculate true sloped roof area from your building footprint and pitch. Get square feet, square metres, roofing squares and a waste-adjusted order quantity.
- Roof Square Footage CalculatorWork out roof square footage from ridge length, rafter length and pitch. Converts to roofing squares, square metres and a bundle count for shingles.
- Sloped Roof Area CalculatorConvert building footprint area to true sloped roof area using the pitch multiplier. Get roofing squares, square metres, and a waste-adjusted order quantity.
- Roof Overhang CalculatorCalculate roof overhang tail length, fascia drop, soffit area and added roof area from the horizontal overhang, pitch and perimeter.
- Roof Height CalculatorCalculate roof rise, ridge height above ground and roof angle from the building span, pitch and wall height.
Framing & Structure
Framing tools work in the same right triangle: run, rise and rafter. Give any two and the rest follow. Results include the plumb and seat cut angles you need at the saw.
- Rafter Length CalculatorCalculate 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.
- Rafter Angle CalculatorCalculate rafter cut angles, birdsmouth size and speed square settings from span and pitch. Get plumb cut, seat cut, rafter length and a cut diagram.
- Roof Truss CalculatorCalculate how many roof trusses you need, plus peak height, top chord length and bottom chord length from your span, pitch and spacing.
- Purlin CalculatorWork out purlin spacing, total linear feet and number of purlins for a metal roof. Includes span, pitch, overhang and common spacing presets.
- Hip Rafter CalculatorCalculate hip rafter length, plumb and side cut angles, and the number of jack rafters for a hip roof from span, pitch and overhang.
- Lean-To Roof CalculatorCalculate a lean-to (skillion) roof's pitch, rafter length, cut angle and roof area from the high wall, low wall and projection.
- Jack Rafter CalculatorCalculate jack rafter lengths, the common difference between them, plumb cut angle and 45° side cut for hip and valley framing.
- Truss Count CalculatorWork out how many roof trusses or rafters you need from building length and spacing. Includes gable end trusses, rafter pairs and a quick cost estimate.
- Attic Truss CalculatorFind the usable room width inside an attic truss from span, pitch, headroom and knee wall height. Shows peak height and room area per foot of length.
Materials & Quantities
Material tools take a roof area and turn it into orderable units — bundles, squares, panels, rolls and sheets — with a waste allowance you control.
- Roof Shingle CalculatorWork out how many shingle bundles and squares your roof needs. Includes waste allowance, starter strip, ridge cap and nail quantities for asphalt shingles.
- Metal Roof CalculatorCalculate metal roofing panels, panel length, screws and trim from your roof dimensions and pitch. Works for standing seam and exposed-fastener panels.
- Roof Tile CalculatorCalculate how many roof tiles, bundles and underlayment rolls you need for clay, concrete or Spanish tile roofs from footprint, pitch and waste.
- Underlayment CalculatorCalculate how many rolls of roofing underlayment you need for any roof area. Supports #15 felt, synthetic and ice-and-water shield coverage widths.
- Roofing Nails CalculatorEstimate roofing nails or screws by weight and count for shingles, metal panels and underlayment. Supports 4-nail and 6-nail patterns.
- Roof Sheathing CalculatorCalculate how many plywood or OSB roof sheathing sheets you need from roof area, sheet size and waste. Supports 4×8 and metric panels.
- Ice and Water Shield CalculatorCalculate ice and water shield rolls needed from eave length, roof pitch, valley length and IRC R905.1.2's 24 inch inside-the-wall rule.
- Drip Edge CalculatorCalculate drip edge pieces needed for eaves and rakes from standard 10 ft lengths, overlap and waste, plus the nails required to install it.
- Metal Roofing Screws CalculatorCalculate how many metal roofing screws you need from roof area, panel width and purlin spacing. Gives screws per square, total screws and bags of 250.
Cost & Estimating
Cost tools separate materials, labour, tear-off and disposal so you can see what actually drives a quote. Change any rate to match a real bid you have in hand.
Load, Drainage & Performance
Load and drainage tools apply published code methods — ASCE 7 for snow and wind, IPC for drainage — to your roof geometry. They size for a first-pass check, not a stamped design.
- Snow Load CalculatorCalculate 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.
- Gutter Slope CalculatorCalculate 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.
- Gutter Size CalculatorSize gutters and downspouts from roof area, pitch and local rainfall intensity. Get recommended gutter profile, downspout count and capacity check.
- Ridge Vent CalculatorCalculate ridge vent length and net free vent area for balanced attic ventilation. Matches intake vent area and gives code-compliant NFVA guidance.
- Attic Ventilation CalculatorCalculate attic ventilation NFVA, soffit vent count and gable vent size from attic area using the IRC 1:150 and 1:300 intake/exhaust ratios.
- Downspout CalculatorCalculate how many downspouts you need and what size to use based on roof area, rainfall intensity and downspout capacity per IPC guidance.
- Flat Roof Fall CalculatorCalculate flat roof fall from a slope ratio like 1:40 or 1:60. Get total drop, percentage grade, degrees and inches of fall per foot of run.