Answers
A calculator waits for you to type. These pages do not: each one takes a question with a number in it, states the number, shows how it was worked out, and gives you the surrounding cases in a table. Every figure is computed by the same functions the calculators run on, so nothing here can drift away from the tool it links to.
Lumber and sheet goods
What is the actual size of a 2x4?
A 2x4 is actually 1 1/2" × 3 1/2".
How many board feet are in a 2x4?
An 8' 2x4 is 5.33 board feet.
What is the difference between a board foot and a linear foot?
A linear foot measures length only; a board foot measures volume — 144 cubic inches, or a piece 12" × 12" × 1".
How much does a 2x4 weigh?
An 8' kiln-dried Douglas fir 2x4 weighs about 9.9 lb.
How much does a sheet of plywood weigh?
A 4' × 8' sheet of 3/4" softwood plywood weighs about 72 lb.
How much does a wide board move with the seasons?
A 12" plain-sawn white oak board moves about 5/16" across its width.
How many pieces can I cut from a board?
An 8' board yields 5 pieces at 16", not 6.
How many panels fit on a sheet of plywood?
A 4' × 8' sheet holds 3 parts at 24" × 30", but 6 at 23 3/4" × 30".
Fasteners
What size pilot hole for a #8 screw?
A #8 screw wants a 3/32" pilot in hardwood and 5/64" in softwood.
What length pocket hole screw for 3/4" stock?
3/4" stock takes a 1 1/4" pocket screw.
How many deck screws per square foot?
About 3.9 screws per square foot, at 16" joist spacing.
How many screws to fasten a sheet of plywood?
A 4' × 8' sheet takes 80 fasteners at 6" edges and 12" field.
Joinery
How thick should a tenon be?
A third of the stock thickness: 3/4" material gives a 1/4" tenon.
What angle should dovetails be cut at?
1:6 for softwood (9.5° from square) and 1:8 for hardwood (7.1°).
What angle do you cut segments for a turned ring?
A 12-segment flat ring is cut at 15.0° on each end of every segment.
How many boards for a 24 inch panel?
A 24" panel from 6" boards takes 5 of them, once each edge loses 1/16".
Angles and trim
What angle do you cut 38° crown molding at?
Miter 31.6°, bevel 33.9° — cutting 38° crown flat on the saw table in a square corner.
How do I find the spring angle of a piece of crown molding?
Drop 2 1/2", reach 1 15/16" — that molding's spring angle is 37.8°, close enough to call it 38°.
What miter angle for a six-sided frame?
Every piece of a six-sided frame is cut at 30.0° on each end.
What angle do you cut a sloped box or hopper at?
A 4-sided box with its walls sloped 45.0° from horizontal is cut at 35.3° miter and 30.0° bevel.
What miter for a corner that isn't 90 degrees?
Cut each piece at half of what is left from 180° — a 92° corner takes 44.0° per side, not 45.0°.
How much molding do I need for a picture frame?
A 16" × 20" opening in 2" molding takes 20" and 24" pieces, long point to long point.
How high should wainscoting be?
About a third of the wall height: 32" on an 8-foot wall, measured to the top of the chair rail.
How much baseboard do I need for a room?
A 12' × 14' room takes 4 sticks of 16' baseboard.
Stairs and framing
How many stairs for an 8 foot ceiling?
96" of rise takes 14 risers at 6 7/8", which is 13 treads.
What is the standard stair riser height and tread depth?
The IRC maximum riser is 7 3/4" and the minimum tread depth is 10".
How long a board do I need for a stair stringer?
108" of rise over 11 ft 8 in of run gives a stringer 14 ft 8 13/16 in long — buy 16'.
How high should a stair handrail be?
34" to 38", measured vertically from the sloped line through the tread nosings.
How many studs in a 10 foot wall?
A 10' wall at 16" on centre takes 9 field studs — 12 in total with one three-stud corner.
How long is a rafter on a 6/12 pitch?
A 6/12 pitch gives 13.4164" of common rafter per foot of run.
What is the rough opening size for a door?
A 2' 8" × 6' 8" door wants a rough opening about 34" wide by 82" to 82 1/2" tall.
Shelving and cabinets
How far can a 3/4 inch shelf span before it sags?
About 39 5/16" between supports, for 3/4" hardwood plywood carrying 25 lb of books per foot.
How many hinges does a cabinet door need?
A door up to 30" tall takes 2 hinges; over that, 3 to 48" and 4 to 72".
What size drawer box for a 24 inch opening?
A 24" opening takes a 23" box on side-mount slides.
What are standard kitchen cabinet dimensions?
A base cabinet is 34 1/2" high and 24" deep — 36" once a countertop is on it.
What size are the parts for a 24 inch base cabinet?
The sides are 30 1/2" × 24" and the bottom is 22 1/2" × 24", for a 24" box.
How much countertop overhang needs support?
6" is the usual unsupported limit — 10" for 3cm stone.
How far apart should shelf pin holes be?
32mm system: holes every 1 1/4", which is what every piece of European cabinet hardware is drilled for.
How high should a closet rod be?
68" floor to rod for a single-hang closet, with the shelf at 80".
Layout and measuring
How do you check a corner is square?
Measure 3 units along one side and 4 along the other; square, the diagonal between the marks is exactly 5.
How do you find the radius of an arch?
A 36" opening bowing 4" at the middle is struck from a radius of 42 1/2".
How do you scale up a pattern from a drawing?
A 1/4"-square grid, 16 squares wide, blown up to 32" means drawing the big grid at 2" a square.
How do you convert a decimal to inches and fractions?
Multiply by 16 and round: 0.375 × 16 = 6, so 0.375" is 3/8".
Roofing, outdoor and finishing
How many bundles of shingles do I need?
A 28' × 40' house at 6/12 takes 47 bundles — 15.5 squares.
How do you work out roof area from the floor plan?
Plan area × the slope factor. At 6/12 that factor is 1.1180, so a 30' × 40' footprint is 1503 ft² of roof.
How many bags of concrete for a fence post?
One 10" hole 30" deep takes 3 bags of 60 lb mix.
How much concrete for a 12x12 slab?
A 12' × 12' slab 4" thick takes 1.78 cubic yards.
How far apart should fence posts be?
A 100' run at no more than 8' between posts takes 14 posts, landing 7 ft 8 5/16 in apart.
How many deck boards for a 12x16 deck?
A 12' × 16' deck takes 26 rows of 5/4 x 6 (5 1/2" wide).
How far apart should deck joists be?
16" on centre suits composite and 5/4 decking; 24" is the limit for a full 1 1/2" board.
How much paint for a 12x12 room?
About 2.2 gallons for two coats — buy 2 gallons and 1 quart.
How many tiles for a 10x10 room?
A 10' × 10' floor in 12" tile takes 121 tiles, or 134 with 10% for breakage and cuts.
How much flooring do I need for a room?
A 12' × 14' room takes 29 rows of 5" board, covering 168 ft² before waste.
How many balusters for a deck railing?
A 6' clear span takes 14 1 1/2" balusters, at 3 3/8" between them.
Wood species
What is the hardest common wood species?
Hickory is the hardest of the fourteen species this site has data for, at 1820 lbf on the Janka scale.
Which wood species moves least with the seasons?
White pine moves the least of the fourteen species here — about 3/16" across a 12" flat-sawn board between 30% and 70% relative humidity.
What is the cheapest common wood species?
Poplar and White pine tie for cheapest, at $4/bf — an 8' 1x6 in either costs about $21 bought as rough 4/4 stock.
What is the heaviest common wood species?
Hickory is the heaviest of the fourteen species this site has data for — an 8' 1x6 in it weighs about 17.0 lb, kiln-dried.
How much heavier is green wood than kiln-dried?
Green walnut is about 59% heavier than the same board kiln-dried — the biggest gap of the fourteen species here.