Construction calculators
Free web calculators for the math a carpenter actually runs, each one built from the CutOnce app's tested code, with the stair calculator checked against IRC R311.7. No sign-up, works on your phone on the jobsite.
Updated
- CALC. 01
Stair stringer calculator
One total-rise measurement in, the whole stair out: riser height, tread depth, and stringer length, each checked against IRC R311.7.
Open calculator → - CALC. 02
Rafter length calculator
Span and pitch in, common rafter out: line length, ridge deduction, overhang tail, the birdsmouth seat and plumb cuts, HAP, and both saw angles.
Open calculator → - CALC. 03
Roof pitch calculator
Convert a pitch between rise per 12, degrees, percent, and ratio, in either direction, with a common-pitch conversion table.
Open calculator → - CALC. 04
Feet and inches calculator
Add, subtract, multiply, and divide feet-inch-fraction measurements the way a tape reads, rounded to the nearest sixteenth.
Open calculator → - CALC. 05
Board foot calculator
Board feet for any lumber size and quantity, figured from nominal dimensions, with a nominal-vs-actual size table.
Open calculator → - CALC. 06
Birdsmouth cut calculator
The seat cut, plumb cut, and HAP for a common rafter's birdsmouth, with a warning when the notch would cut through the rafter.
Open calculator → - CALC. 07
Hip rafter calculator
Hip length, run, and every cut angle from a building width and pitch, plus the backing angle and the jack rafter run-down.
Open calculator → - CALC. 08
Valley rafter calculator
Valley length, run, and every cut angle from an intersecting span and pitch, plus the jack rafter common difference and run-down.
Open calculator → - CALC. 09
Deck stair calculator
The whole deck stair from one measurement, the rise from the decking to the landing: riser height, tread depth, and stringer length, checked against IRC R311.7.
Open calculator → - CALC. 10
Drywall calculator
Sheets of drywall for a room from its dimensions, with doors and windows taken out, a waste factor, and any US sheet size.
Open calculator → - CALC. 11
Rise over run calculator
A rise and run read as an x/12 pitch, an angle in degrees, a percent grade, and the diagonal, the triangle math under every stair and roof.
Open calculator → - CALC. 12
Roofing squares calculator
Roof area in squares, shingle bundles, sheathing, and underlayment from a footprint and pitch, with the pitch factor and a waste allowance.
Open calculator → - CALC. 13
Deck board calculator
Decking boards for a deck from its size and board width, with straight or diagonal layout, a waste factor, deck area, and a face-screw estimate.
Open calculator → - CALC. 14
Baluster spacing calculator
How many balusters a rail needs and the even gap between them, spaced so no 4-inch sphere passes, the IRC guard rule, on deck and stair rails.
Open calculator → - CALC. 15
Stud calculator
Wall studs from length and on-center spacing, with plate stock, plus rake and gable wall stud counts and lengths stepped up the roof pitch.
Open calculator → - CALC. 16
Crown molding angle calculator
Compound miter and bevel to cut crown flat, or the single nested miter, from the spring angle and any wall corner, square or not.
Open calculator → - CALC. 17
Concrete calculator
Concrete for a slab, footing, or column in cubic yards, cubic feet, and bag counts, with a waste factor and a ready-mix threshold.
Open calculator → - CALC. 18
Area calculator
Square footage of a room, slab, or lot in square feet, square yards, and square meters, plus circle area and cylinder volume in cubic feet and gallons.
Open calculator → - CALC. 19
Masonry calculator
Concrete blocks or bricks a wall takes, the mortar bags to lay them, and the course layout, with door and window openings and a waste factor.
Open calculator → - CALC. 20
Rebar calculator
Reinforcing steel for a slab, footing, or pier: bar count, lengths after cover, total feet, stock sticks, and weight, with spacing and lap splices.
Open calculator → - CALC. 21
Concrete weight calculator
Weight of a concrete pour in pounds, short tons, and kilograms from slab dimensions or a known volume, across standard, reinforced, and lightweight mixes.
Open calculator →
The same math the app runs
Every calculator here shares its arithmetic with the CutOnce app, and the app's numbers are checked against the app's own test suite on every build. The worked examples on each page are computed by that shared code, not typed in, so the page cannot say one thing while the calculator does another.
Choosing an app instead?
CutOnce vs Construction Master Pro
The classic handheld's app against CutOnce, side by side: entry model, stairs, rafters, code checks, and output, with an honest call on which to buy.
Read the comparison →Best construction calculator apps
An honest roundup of the apps worth installing, including our competitors, judged on entry model, framing depth, and what you walk away with.
Read the comparison →
The whole toolbox, offline
The web pages are a taste. The app carries the full toolbox: stairs, rafters, and roof framing plus materials, concrete, drywall, decks, and unit conversions, a tape that keeps 500 calculations, and printable PDF plans, all working with no signal.
