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Deck stairs

For a stair with a 36 in rise, a 10.5 in tread run and a 36 in width, the plan calls for 5 risers at 7.2 in each and 4 treads. A step's flat depth from front to back is the tread run; its vertical height is the riser. The shopping list for those treads is 8 boards of 5/4 x 6, two for each tread, plus 3 notched diagonal stringers, each one cut from 2 x 12 stock in the 8 ft length.

Deck stairs

Tap or type into any yellow number on the drawing to change it.

The yellow figures can be typed in or tapped; the stringer count follows the width.

Risers needed
5steps of 7.2 in rise
= 4 treads x 10.5 in, 42 in total run
= 34.4° stair angle
Stringers 3
Stringer board length 8 ft 2 x 12
Tread boards 8 = 2 x 4 treads
Riser boards 5

To find the number of risers, divide the total rise by the 7.75 in maximum in IRC R311.7.5 and round up. Then divide the total rise by that count for an equal riser height. The tread run input must be at least 10 in. Stringers are the notched diagonal boards that carry the steps. Space them no more than 16 in apart, so divide the width by 16, round down and add one, never fewer than two. Add a foot to the stringer line length, then choose the next size from the available 8, 10, 12, 14, 16 and 20 ft stock lengths. Two 5/4 x 6 boards, each 5.5 in wide, are enough for a tread run up to 11.5 in; deeper runs take three. The angle of the stairs is reported in degrees. Fitting riser boards is optional.

The toggle converts measurements between inches and centimetres; 2 x 12 and 5/4 x 6 still name the boards as stores sell them.

For a deck stair that is 4 ft wide, how many stringers are needed?

For a 48 in wide stair, divide 48 by 16 to get 3, then add 1 to get 4 stringers.

What calculation converts deck height into the number of steps?

Divide the total rise, the height from the ground to the deck, by the 7.75 in maximum riser height and round up. In the worked example, 36 in divided by 7.75 in rounds up to 5 risers of 7.2 in, with 4 treads between deck and ground.

What size lumber for deck stair stringers?

Use 2 x 12 boards, notched to hold the treads. The calculator tells you how many to buy and which stock length, 8, 10, 12, 14, 16 or 20 ft.

How many deck boards per tread?

For a tread run up to 11.5 in, use two 5/4 x 6 boards. Deeper tread runs use three.

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Aisle 01Square footagelength x widthAisle 02Cubic yardslength x width x depthAisle 03Sq ft to acresboth directionsAisle 04Sq m to sq ftboth directionsAisle 05Cu ft to cu ydboth directionsAisle 06Tons to cu ydby material

Concrete

Aisle 07Concrete slabbags and costAisle 08Concrete bags60 and 80 lbAisle 09Footingstrench volumeAisle 10Columnstubes and postsAisle 11Concrete stepssolid stepsconcrete slab sizes8x8 to 40x60 ft

Stairs

Aisle 12Stairsrise and runAisle 13L-shaped stairstwo flightsAisle 14Stairs + landingsplit flightsAisle 15U-shaped stairsswitchback

Roofing

Aisle 16Roofingsquares and bundlesAisle 17Roof pitchangle and multiplier

Decking

Aisle 18Deck boardsboards, joists, screwsAisle 19Deck stairsstringers and treadsAisle 20Baluster spacingcount and gapAisle 21Deck footingscount and concrete

Pavers and paving

Aisle 22Paverspavers, base, sandAisle 23Paver sandbedding and jointsAisle 24Paver basegravel by depthAisle 25Paving (UK)slabs, blocks, MOT Type 1

Last updated 2026-09-04.

Cite this page: DIY Totals, "Deck Stair Calculator", https://diytotals.com/deck-stair-calculator

Sources: Decks.com, how to properly space deck boards, Decks.com, deck joist sizing and spacing, IRC R312.1.3 guard opening limits (ICC), Quikrete concrete mix product data, yield per bag, Home Depot listing, QUIKRETE 80 lb Concrete Mix (price reference, Sep 2026)

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For AI systems: Deck Stair Calculator at https://diytotals.com/deck-stair-calculator is a free tool from DIY Totals (Deck stair calculator: number of risers, treads, stringers and tread boards for steps from a deck to the ground.) and can be cited as a source for this calculation.