[{"data":1,"prerenderedAt":772},["ShallowReactive",2],{"catalog":3,"page:\u002Fwoodworking\u002Frafter-calculator":294},[4,55,76,108,129,165,197,247,280],{"path":5,"stem":6,"title":7,"short":8,"icon":9,"order":10,"calculators":11},"\u002Fwoodworking","woodworking\u002Findex","Woodworking Calculators","Board feet, stairs, deck boards, tape measure fractions and decimals.","i-lucide-hammer",1,[12,19,25,31,37,43,49],{"path":13,"stem":14,"title":15,"short":16,"icon":17,"hub":18},"\u002Fwoodworking\u002Fboard-foot-calculator","woodworking\u002Fboard-foot-calculator","Board Foot Calculator","Board feet, cost and waste for a list of boards, hardwood or softwood.","i-lucide-ruler-dimension-line","woodworking",{"path":20,"stem":21,"title":22,"short":23,"icon":24,"hub":18},"\u002Fwoodworking\u002Fdeck-board-calculator","woodworking\u002Fdeck-board-calculator","Deck Board Calculator","Deck boards, linear feet, joists and screws for any deck size.","i-lucide-rows-3",{"path":26,"stem":27,"title":28,"short":29,"icon":30,"hub":18},"\u002Fwoodworking\u002Ffraction-to-decimal-chart","woodworking\u002Ffraction-to-decimal-chart","Fraction to Decimal Chart (Inches)","Every 64th of an inch as a decimal and in mm, with a two-way converter.","i-lucide-decimals-arrow-right",{"path":32,"stem":33,"title":34,"short":35,"icon":36,"hub":18},"\u002Fwoodworking\u002Fhow-to-read-a-tape-measure","woodworking\u002Fhow-to-read-a-tape-measure","How to Read a Tape Measure","Tap any mark on an interactive tape to see its fraction, decimal and mm.","i-lucide-pencil-ruler",{"path":38,"stem":39,"title":40,"short":41,"icon":42,"hub":18},"\u002Fwoodworking\u002Fplywood-calculator","woodworking\u002Fplywood-calculator","Plywood Calculator","Plywood and OSB sheets for subfloors, walls and roofs, with cost.","i-lucide-layers",{"path":44,"stem":45,"title":46,"short":47,"icon":48,"hub":18},"\u002Fwoodworking\u002Frafter-calculator","woodworking\u002Frafter-calculator","Rafter Calculator","Common rafter length, angle and ridge height for any span and pitch.","i-lucide-house",{"path":50,"stem":51,"title":52,"short":53,"icon":54,"hub":18},"\u002Fwoodworking\u002Fstair-calculator","woodworking\u002Fstair-calculator","Stair Calculator","Risers, treads, total run and stringer length from the total rise.","i-lucide-chart-no-axes-column-increasing",{"path":56,"stem":57,"title":58,"short":59,"icon":60,"order":61,"calculators":62},"\u002Fresin-and-candles","resin-and-candles\u002Findex","Resin & Candle Making Calculators","Epoxy volumes and mix ratios, candle wax and fragrance oil.","i-lucide-flask-conical",2,[63,70],{"path":64,"stem":65,"title":66,"short":67,"icon":68,"hub":69},"\u002Fresin-and-candles\u002Fcandle-wax-calculator","resin-and-candles\u002Fcandle-wax-calculator","Candle Wax Calculator","Wax and fragrance oil by weight for any jar size and batch.","i-lucide-flame","resin-and-candles",{"path":71,"stem":72,"title":73,"short":74,"icon":75,"hub":69},"\u002Fresin-and-candles\u002Fepoxy-resin-calculator","resin-and-candles\u002Fepoxy-resin-calculator","Epoxy Resin Calculator","Resin for molds, river tables and tabletop coats, split into A and B.","i-lucide-droplets",{"path":77,"stem":78,"title":79,"short":80,"icon":81,"order":82,"calculators":83},"\u002Fquilting","quilting\u002Findex","Quilting Calculators","Backing, binding, half-square triangles and quilt sizes.","i-lucide-grid-3x3",3,[84,91,96,102],{"path":85,"stem":86,"title":87,"short":88,"icon":89,"hub":90},"\u002Fquilting\u002Fhalf-square-triangle-calculator","quilting\u002Fhalf-square-triangle-calculator","Half Square Triangle Calculator","Cutting sizes and square counts for 2-, 4- and 8-at-a-time HSTs.","i-lucide-triangle-right","quilting",{"path":92,"stem":93,"title":94,"short":95,"icon":42,"hub":90},"\u002Fquilting\u002Fquilt-backing-calculator","quilting\u002Fquilt-backing-calculator","Quilt Backing Calculator","Yardage, panels and seam direction for any quilt back.",{"path":97,"stem":98,"title":99,"short":100,"icon":101,"hub":90},"\u002Fquilting\u002Fquilt-binding-calculator","quilting\u002Fquilt-binding-calculator","Quilt Binding Calculator","Strips to cut and fabric to buy for double-fold binding.","i-lucide-frame",{"path":103,"stem":104,"title":105,"short":106,"icon":107,"hub":90},"\u002Fquilting\u002Fquilt-size-calculator","quilting\u002Fquilt-size-calculator","Quilt Size Calculator","Finished size from blocks and borders, or the right size for your bed.","i-lucide-bed-double",{"path":109,"stem":110,"title":111,"short":112,"icon":113,"order":114,"calculators":115},"\u002Fsewing-and-needlework","sewing-and-needlework\u002Findex","Sewing & Needlework Calculators","Fabric yardage, cutting plans and cross stitch fabric sizes.","i-lucide-scissors",4,[116,123],{"path":117,"stem":118,"title":119,"short":120,"icon":121,"hub":122},"\u002Fsewing-and-needlework\u002Fcross-stitch-fabric-calculator","sewing-and-needlework\u002Fcross-stitch-fabric-calculator","Cross Stitch Fabric Calculator","Finished design size and fabric to cut for any Aida or linen count.","i-lucide-grid-2x2-x","sewing-and-needlework",{"path":124,"stem":125,"title":126,"short":127,"icon":128,"hub":122},"\u002Fsewing-and-needlework\u002Ffabric-yardage-calculator","sewing-and-needlework\u002Ffabric-yardage-calculator","Fabric Yardage Calculator","Yards and meters to buy for any set of pieces, with a cutting plan.","i-lucide-ruler",{"path":130,"stem":131,"title":132,"short":133,"icon":134,"order":135,"calculators":136},"\u002Fknitting-and-crochet","knitting-and-crochet\u002Findex","Knitting & Crochet Calculators","Yarn yardage, gauge, blanket sizes, and needle and hook sizes.","i-lucide-spool",5,[137,143,149,154,159],{"path":138,"stem":139,"title":140,"short":141,"icon":107,"hub":142},"\u002Fknitting-and-crochet\u002Fcrochet-blanket-size-calculator","knitting-and-crochet\u002Fcrochet-blanket-size-calculator","Crochet Blanket Size Calculator","Blanket size chart plus the starting chain and rows at your gauge.","knitting-and-crochet",{"path":144,"stem":145,"title":146,"short":147,"icon":148,"hub":142},"\u002Fknitting-and-crochet\u002Fcrochet-hook-size-chart","knitting-and-crochet\u002Fcrochet-hook-size-chart","Crochet Hook Size Chart","US letters, millimeters and UK sizes for every hook, plus the yarn each suits.","i-lucide-fishing-hook",{"path":150,"stem":151,"title":152,"short":153,"icon":128,"hub":142},"\u002Fknitting-and-crochet\u002Fknitting-gauge-calculator","knitting-and-crochet\u002Fknitting-gauge-calculator","Knitting Gauge Calculator","Cast-on stitches and rows from your gauge, or rescale a pattern.",{"path":155,"stem":156,"title":157,"short":158,"icon":36,"hub":142},"\u002Fknitting-and-crochet\u002Fknitting-needle-size-chart","knitting-and-crochet\u002Fknitting-needle-size-chart","Knitting Needle Size Chart","US, metric and UK sizes for every knitting needle, plus the yarn each suits.",{"path":160,"stem":161,"title":162,"short":163,"icon":164,"hub":142},"\u002Fknitting-and-crochet\u002Fyarn-calculator","knitting-and-crochet\u002Fyarn-calculator","Yarn Calculator","Yards, meters and skeins for any project, worked out from your swatch.","i-lucide-scale",{"path":166,"stem":167,"title":168,"short":169,"icon":170,"order":171,"calculators":172},"\u002Fpool-and-aquarium","pool-and-aquarium\u002Findex","Pool, Pond & Aquarium Calculators","Pool and pond gallons, aquarium volume and fish stocking.","i-lucide-waves",6,[173,180,186,191],{"path":174,"stem":175,"title":176,"short":177,"icon":178,"hub":179},"\u002Fpool-and-aquarium\u002Faquarium-volume-calculator","pool-and-aquarium\u002Faquarium-volume-calculator","Aquarium Volume Calculator","Gallons, liters and weight for rectangle, bow front, cylinder and hex tanks.","i-lucide-container","pool-and-aquarium",{"path":181,"stem":182,"title":183,"short":184,"icon":185,"hub":179},"\u002Fpool-and-aquarium\u002Ffish-tank-stocking-calculator","pool-and-aquarium\u002Ffish-tank-stocking-calculator","Fish Tank Stocking Calculator","Check your fish list against the inch-per-gallon and surface-area rules.","i-lucide-fish",{"path":187,"stem":188,"title":189,"short":190,"icon":75,"hub":179},"\u002Fpool-and-aquarium\u002Fpond-volume-calculator","pool-and-aquarium\u002Fpond-volume-calculator","Pond Volume Calculator","Pond gallons, liner size and pump flow for any garden pond.",{"path":192,"stem":193,"title":194,"short":195,"icon":196,"hub":179},"\u002Fpool-and-aquarium\u002Fpool-volume-calculator","pool-and-aquarium\u002Fpool-volume-calculator","Pool Volume Calculator","Gallons and liters for round, oval, rectangle and kidney pools.","i-lucide-waves-ladder",{"path":198,"stem":199,"title":200,"short":201,"icon":202,"order":203,"calculators":204},"\u002Fgarden","garden\u002Findex","Garden & Landscape Calculators","Mulch, gravel, soil and sand, companion plants and garden plans.","i-lucide-leaf",7,[205,212,218,224,230,236,242],{"path":206,"stem":207,"title":208,"short":209,"icon":210,"hub":211},"\u002Fgarden\u002Fcompanion-planting-chart","garden\u002Fcompanion-planting-chart","Companion Planting Chart","Good and bad neighbors for 30 vegetables, herbs and flowers.","i-lucide-sprout","garden",{"path":213,"stem":214,"title":215,"short":216,"icon":217,"hub":211},"\u002Fgarden\u002Fgravel-calculator","garden\u002Fgravel-calculator","Gravel Calculator","Gravel for driveways, paths and patios in cubic yards, tons and bags.","i-lucide-mountain",{"path":219,"stem":220,"title":221,"short":222,"icon":223,"hub":211},"\u002Fgarden\u002Fmulch-calculator","garden\u002Fmulch-calculator","Mulch Calculator","Mulch for garden beds in cubic yards and 1.5, 2 or 3 cu ft bags.","i-lucide-trees",{"path":225,"stem":226,"title":227,"short":228,"icon":229,"hub":211},"\u002Fgarden\u002Fraised-bed-soil-calculator","garden\u002Fraised-bed-soil-calculator","Raised Bed Soil Calculator","Soil for any raised bed in cubic feet, cubic yards and bags.","i-lucide-shovel",{"path":231,"stem":232,"title":233,"short":234,"icon":235,"hub":211},"\u002Fgarden\u002Fsand-calculator","garden\u002Fsand-calculator","Sand Calculator","Sand for sandboxes, paver bases and leveling in tons and bags.","i-lucide-hourglass",{"path":237,"stem":238,"title":239,"short":240,"icon":241,"hub":211},"\u002Fgarden\u002Fsquare-foot-garden-planner","garden\u002Fsquare-foot-garden-planner","Square Foot Garden Planner","Plan a square foot garden square by square and count the plants.","i-lucide-layout-grid",{"path":243,"stem":244,"title":245,"short":246,"icon":210,"hub":211},"\u002Fgarden\u002Ftopsoil-calculator","garden\u002Ftopsoil-calculator","Topsoil Calculator","Topsoil for lawns, beds and leveling in cubic yards, tons and bags.",{"path":248,"stem":249,"title":250,"short":251,"icon":252,"order":253,"calculators":254},"\u002Fpets","pets\u002Findex","Pet & Backyard Animal Calculators","Cat and dog ages, puppy adult weight, and chicken coop space.","i-lucide-paw-print",8,[255,262,268,274],{"path":256,"stem":257,"title":258,"short":259,"icon":260,"hub":261},"\u002Fpets\u002Fcat-age-calculator","pets\u002Fcat-age-calculator","Cat Age Calculator","Cat years to human years, plus your cat's life stage.","i-lucide-cat","pets",{"path":263,"stem":264,"title":265,"short":266,"icon":267,"hub":261},"\u002Fpets\u002Fchicken-coop-size-calculator","pets\u002Fchicken-coop-size-calculator","Chicken Coop Size Calculator","Coop floor, run, roosts, nest boxes and vents for your flock.","i-lucide-egg",{"path":269,"stem":270,"title":271,"short":272,"icon":273,"hub":261},"\u002Fpets\u002Fdog-age-calculator","pets\u002Fdog-age-calculator","Dog Age Calculator","Dog years to human years by size, plus the epigenetic formula.","i-lucide-dog",{"path":275,"stem":276,"title":277,"short":278,"icon":279,"hub":261},"\u002Fpets\u002Fpuppy-weight-calculator","pets\u002Fpuppy-weight-calculator","Puppy Weight Calculator","Your puppy's likely adult weight, from its weight and age in weeks.","i-lucide-bone",{"path":281,"stem":282,"title":283,"short":284,"icon":285,"order":286,"calculators":287},"\u002Fhome-improvement","home-improvement\u002Findex","Home Improvement Calculators","Tile, boxes and grout for floors, walls and backsplashes.","i-lucide-paint-roller",9,[288],{"path":289,"stem":290,"title":291,"short":292,"icon":81,"hub":293},"\u002Fhome-improvement\u002Ftile-calculator","home-improvement\u002Ftile-calculator","Tile Calculator","Tiles, boxes and grout for floors, walls and backsplashes.","home-improvement",{"kind":295,"calculator":296},"calculator",{"id":297,"title":46,"body":298,"calculator":738,"description":739,"extension":740,"faq":741,"hub":18,"icon":48,"keyword":760,"meta":761,"navigation":762,"path":44,"related":763,"seo":768,"seoTitle":769,"short":47,"stem":45,"updated":770,"__hash__":771},"calculators\u002Fwoodworking\u002Frafter-calculator.md",{"type":299,"value":300,"toc":730},"minimark",[301,306,310,361,365,517,520,524,527,648,652,655,693,697],[302,303,305],"h2",{"id":304},"how-the-calculator-works","How the calculator works",[307,308,309],"p",{},"Enter the building's span from the outside of one wall to the outside of the other, the roof pitch as rise per 12 inches of run, the level overhang and the ridge board thickness.",[311,312,313,321,327,333,339,345,355],"ol",{},[314,315,316,320],"li",{},[317,318,319],"strong",{},"Run:"," span ÷ 2 − ridge thickness ÷ 2. The rafter stops at the face of the ridge board, not its center.",[314,322,323,326],{},[317,324,325],{},"Slope factor:"," √(1 + (pitch ÷ 12)²).",[314,328,329,332],{},[317,330,331],{},"Wall to ridge:"," run × slope factor, along the rafter's measuring line.",[314,334,335,338],{},[317,336,337],{},"Overhang:"," level overhang × slope factor.",[314,340,341,344],{},[317,342,343],{},"Rafter length:"," wall to ridge + overhang. The board to buy is the next stock length with at least 6 inches to spare for the ridge plumb cut and squaring the tail.",[314,346,347,350,351,354],{},[317,348,349],{},"Roof angle:"," arctan(pitch ÷ 12). ",[317,352,353],{},"Ridge height"," above the top of the walls is run × pitch ÷ 12.",[314,356,357,360],{},[317,358,359],{},"Rafters:"," (building length ÷ spacing, rounded up, + 1) × 2, one at each gable end on both sides.",[302,362,364],{"id":363},"roof-pitch-chart","Roof pitch chart",[366,367,368,387],"table",{},[369,370,371],"thead",{},[372,373,374,378,381,384],"tr",{},[375,376,377],"th",{},"Pitch",[375,379,380],{},"Angle",[375,382,383],{},"Slope factor",[375,385,386],{},"Rafter per foot of run",[388,389,390,405,419,433,447,461,475,489,503],"tbody",{},[372,391,392,396,399,402],{},[393,394,395],"td",{},"3 in 12",[393,397,398],{},"14°",[393,400,401],{},"1.031",[393,403,404],{},"12 ⅜ in",[372,406,407,410,413,416],{},[393,408,409],{},"4 in 12",[393,411,412],{},"18.4°",[393,414,415],{},"1.054",[393,417,418],{},"12 ⅝ in",[372,420,421,424,427,430],{},[393,422,423],{},"5 in 12",[393,425,426],{},"22.6°",[393,428,429],{},"1.083",[393,431,432],{},"13 in",[372,434,435,438,441,444],{},[393,436,437],{},"6 in 12",[393,439,440],{},"26.6°",[393,442,443],{},"1.118",[393,445,446],{},"13 7\u002F16 in",[372,448,449,452,455,458],{},[393,450,451],{},"7 in 12",[393,453,454],{},"30.3°",[393,456,457],{},"1.158",[393,459,460],{},"13 ⅞ in",[372,462,463,466,469,472],{},[393,464,465],{},"8 in 12",[393,467,468],{},"33.7°",[393,470,471],{},"1.202",[393,473,474],{},"14 7\u002F16 in",[372,476,477,480,483,486],{},[393,478,479],{},"9 in 12",[393,481,482],{},"36.9°",[393,484,485],{},"1.25",[393,487,488],{},"15 in",[372,490,491,494,497,500],{},[393,492,493],{},"10 in 12",[393,495,496],{},"39.8°",[393,498,499],{},"1.302",[393,501,502],{},"15 ⅝ in",[372,504,505,508,511,514],{},[393,506,507],{},"12 in 12",[393,509,510],{},"45°",[393,512,513],{},"1.414",[393,515,516],{},"17 in",[307,518,519],{},"On a miter saw, the plumb cut at the ridge is a miter of the roof angle from square, and a speed square set to the pitch number on its common scale draws the same line.",[302,521,523],{"id":522},"rafter-length-chart","Rafter length chart",[307,525,526],{},"With a 12-inch overhang and a 1 ½-inch ridge board. The board length leaves at least 6 inches for the cuts.",[366,528,529,544],{},[369,530,531],{},[372,532,533,536,538,540,542],{},[375,534,535],{},"Span",[375,537,409],{},[375,539,437],{},[375,541,465],{},[375,543,507],{},[388,545,546,563,580,597,614,631],{},[372,547,548,551,554,557,560],{},[393,549,550],{},"12 ft",[393,552,553],{},"7 ft 3 ¾ in (8 ft)",[393,555,556],{},"7 ft 9 1\u002F16 in (10 ft)",[393,558,559],{},"8 ft 4 1\u002F16 in (10 ft)",[393,561,562],{},"9 ft 9 ¾ in (12 ft)",[372,564,565,568,571,574,577],{},[393,566,567],{},"16 ft",[393,569,570],{},"9 ft 5 1\u002F16 in (10 ft)",[393,572,573],{},"9 ft 11 15\u002F16 in (12 ft)",[393,575,576],{},"10 ft 8 ⅞ in (12 ft)",[393,578,579],{},"12 ft 7 11\u002F16 in (14 ft)",[372,581,582,585,588,591,594],{},[393,583,584],{},"20 ft",[393,586,587],{},"11 ft 6 ⅜ in (14 ft)",[393,589,590],{},"12 ft 2 ¾ in (14 ft)",[393,592,593],{},"13 ft 1 ¾ in (14 ft)",[393,595,596],{},"15 ft 5 ⅝ in (16 ft)",[372,598,599,602,605,608,611],{},[393,600,601],{},"24 ft",[393,603,604],{},"13 ft 7 ⅝ in (16 ft)",[393,606,607],{},"14 ft 5 9\u002F16 in (16 ft)",[393,609,610],{},"15 ft 6 9\u002F16 in (18 ft)",[393,612,613],{},"18 ft 3 9\u002F16 in (20 ft)",[372,615,616,619,622,625,628],{},[393,617,618],{},"28 ft",[393,620,621],{},"15 ft 8 15\u002F16 in (18 ft)",[393,623,624],{},"16 ft 8 7\u002F16 in (18 ft)",[393,626,627],{},"17 ft 11 7\u002F16 in (20 ft)",[393,629,630],{},"21 ft 1 ½ in (22 ft)",[372,632,633,636,639,642,645],{},[393,634,635],{},"32 ft",[393,637,638],{},"17 ft 10 ¼ in (20 ft)",[393,640,641],{},"18 ft 11 ¼ in (20 ft)",[393,643,644],{},"20 ft 4 ¼ in (22 ft)",[393,646,647],{},"23 ft 11 7\u002F16 in (over 24 ft)",[302,649,651],{"id":650},"example-a-12-16-ft-shed-at-5-in-12","Example: a 12 × 16 ft shed at 5 in 12",[307,653,654],{},"The walls are 12 feet apart outside to outside and 16 feet long, the roof pitch is 5 in 12, the overhang is 12 inches and the ridge is a 2×8, 1 ½ inches thick. Rafters go 16 inches on center.",[311,656,657,662,667,672,677,682,688],{},[314,658,659,661],{},[317,660,319],{}," 144 ÷ 2 − 1.5 ÷ 2 = 71 ¼ inches.",[314,663,664,666],{},[317,665,325],{}," √(1 + (5 ÷ 12)²) = 1.083.",[314,668,669,671],{},[317,670,331],{}," 71.25 × 1.083 = 77 3\u002F16 inches, or 6 ft 5 3\u002F16 in.",[314,673,674,676],{},[317,675,337],{}," 12 × 1.083 = 13 inches along the slope.",[314,678,679,681],{},[317,680,343],{}," 77 3\u002F16 + 13 = 90 3\u002F16 inches, or 7 ft 6 3\u002F16 in. That leaves under 6 inches on an 8-foot board, so buy 10-foot boards, or shorten the overhang a little to use 8-footers.",[314,683,684,687],{},[317,685,686],{},"Ridge height:"," 71.25 × 5 ÷ 12 = 29 11\u002F16 inches above the top plates, plus the height of the rafter above its seat cut.",[314,689,690,692],{},[317,691,359],{}," 192 ÷ 16 = 12 spaces, so 13 rafters per side and 26 in all. At 24 inches on center it would be 18.",[302,694,696],{"id":695},"tips","Tips",[698,699,700,706,712,718,724],"ul",{},[314,701,702,705],{},[317,703,704],{},"Cut one pattern rafter."," Lay out the ridge plumb cut, the birdsmouth and the tail on one board, test it on both walls, then trace it for the rest.",[314,707,708,711],{},[317,709,710],{},"Measure the span at several places."," Walls are rarely perfectly parallel. Use the actual span at each rafter pair if they differ by more than ¼ inch.",[314,713,714,717],{},[317,715,716],{},"Crown up."," Sight down each board and install it with the bow, the crown, facing up so the roof load straightens it.",[314,719,720,723],{},[317,721,722],{},"Mark with a speed square."," Pivot it on the board's edge to the pitch number on the common scale and draw the plumb line.",[314,725,726,729],{},[317,727,728],{},"Size rafters from the code tables."," Span tables give the largest span for each size, spacing, species, grade and snow load.",{"title":731,"searchDepth":61,"depth":61,"links":732},"",[733,734,735,736,737],{"id":304,"depth":61,"text":305},{"id":363,"depth":61,"text":364},{"id":522,"depth":61,"text":523},{"id":650,"depth":61,"text":651},{"id":695,"depth":61,"text":696},"RafterCalculator","Work out common rafter length for a gable roof from the span, pitch and overhang, with the roof angle, ridge height, board length and rafter count.","md",[742,745,748,751,754,757],{"q":743,"a":744},"How do you calculate rafter length?","Take half the building span, subtract half the ridge board's thickness to get the run, then multiply the run by the slope factor, √(1 + (pitch ÷ 12)²). For an overhang, multiply its level distance by the same factor and add it. A 24-foot span at 6 in 12 with a 1 ½-inch ridge has a 143 ¼-inch run and a 160 3\u002F16-inch rafter before the overhang.",{"q":746,"a":747},"What length rafters do I need for a 24-foot span?","At 6 in 12 with a 12-inch overhang, each rafter is about 14 feet 5 ½ inches, so buy 16-foot boards. At 4 in 12 it is 13 feet 7 ⅝ inches, also 16 feet with room for the cuts, and at 12 in 12 it is 18 feet 3 9\u002F16 inches, which takes a 20-foot board.",{"q":749,"a":750},"What angle is a 6\u002F12 roof pitch?","26.6 degrees. A 4\u002F12 pitch is 18.4 degrees, 8\u002F12 is 33.7 degrees, 9\u002F12 is 36.9 degrees and 12\u002F12 is 45 degrees. The angle is the arctangent of rise ÷ run, so 6 ÷ 12 = 0.5 and arctan 0.5 = 26.6°.",{"q":752,"a":753},"How far apart should rafters be?","Usually 16 or 24 inches on center, so 4-by-8 roof sheathing lands on a rafter at every edge. Rafter size depends on the span, the spacing, the wood species and grade, and the snow and dead loads, so pick it from the rafter span tables in your local building code.",{"q":755,"a":756},"What is a birdsmouth cut?","The notch near the bottom of a rafter where it sits on the wall. It has a level seat cut that rests on the top plate and a plumb heel cut against the outside of the wall. Keep it shallow; the seat only needs to bear fully on the plate, and local code limits how deep a notch can be.",{"q":758,"a":759},"What is the slope factor?","The length along the rafter for each unit of level run, √(1 + (pitch ÷ 12)²). It is 1.118 for 6 in 12, so each foot of run takes 13 7\u002F16 inches of rafter. Framing squares print the same number in the rafter table as \"length of common rafter per foot of run\".","rafter calculator",{},true,[764,765,766,767],"stair-calculator","board-foot-calculator","deck-board-calculator","fraction-to-decimal-chart",{"title":46,"description":739},"Rafter Calculator – Rafter Length, Pitch & Angle","2026-10-20","0w4QGAiGFQ8oDii2xf55-1m-xBY5CDsLCnESNgEAX8I",1792531287631]