Decks & stairs calculators
Lay out a deck from footings to boards, then the stairs down from it. Every span and riser is checked against the residential code.
Stair Calculator
Enter the height from floor to floor and get risers, treads, run, stringer length and a to-scale drawing checked against the code.
Open the Stair CalculatorStairs
Stair Calculator
Enter the height from floor to floor and get risers, treads, run, stringer length and a to-scale drawing checked against the code.
Stair Stringer Calculator
Enter the total rise and stair width to get the framing square settings, cut marks, throat depth, board length and stringer count.
Stair Landing Calculator
Pick straight, L or U, enter the rise and stair width, and get both flights, the landing height and size and the plan footprint.
Spiral Staircase Calculator
Enter the diameter, floor-to-floor height and turn to get treads, rise, walkline tread width and headroom, checked against IRC R311.7.10.1.
Stair Tread Calculator
Stair risers = total rise ÷ 7½ in, rounded, and treads = risers − 1: a 9 ft rise needs 14 risers, 13 treads and 14 riser boards on a 36 in wide stair.
Stair Runner Calculator
Runner length = steps × (tread + nosing + riser) plus landings and half a step spare: 14 steps of 18.7 in come to 22 ft 7 in, so buy 23 ft (7⅔ yards).
Decks
Deck Calculator
For building a deck, not a card deck: enter its size and height to get boards, joists, beam, posts, footings, concrete and hardware, checked against the IRC.
Deck Board Calculator
Enter the deck size, board and direction to get boards by length, butt joints over joists, screws or hidden clips and a board layout drawing.
Deck Joist Span Calculator
Pick lumber, joist size and spacing to see the allowable joist span, cantilever and beam span from the IRC deck tables, plus how many joists you need.
Deck Footing Calculator
Enter the beam span, joist span and soil to get the load on each post, the IRC footing size, the hole depth and the concrete bags for every footing.
Deck Stain Calculator
Enter the deck, railing and steps, pick a stain, and get the square footage, gallons per coat and how many gallons and 5-gallon pails to buy.
Railings
Baluster Spacing Calculator
Baluster count = (space between posts − max gap) ÷ (baluster width + max gap), rounded up: 6 ft between posts with 1½ in balusters takes 13 with 3¾ in gaps.
Deck Railing Calculator
Railing posts = one per section plus one per run, less shared corners: a 16 × 12 ft deck railed on three sides with a 4 ft stair opening needs 8 posts at 6 ft spacing.