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Deck Stair Calculator

Plan steps from a deck down to the yard. The calculator accounts for ground that slopes away from the deck, a landing pad, and treads made from deck boards, and shows where the bottom step will land.

Deck and ground

Units
Top of the decking down to the ground directly below the deck edge where the stair starts.
Ground in front of the deck
Measured level, away from the deck.
Top of the concrete pad or pavers above the surrounding ground. 0 if the stair lands on the ground.
Treads
5 1/2 in for a 2x6 or 5/4x6.

6 risers of 6 7/8 in, 5 treads, landing 4 ft 4 1/2 in from the deck, actual rise 3 ft 5 1/8 in. Drawing and details

More options
1 in for 5/4 decking, 1 1/2 in for 2x.
At the deck
On centre. AWC's DCA 6 deck guide uses 18 in.
Lay out the stringers

Worked example: edit any value

Deck stair

Risers6
Riser height≈ 6 7/8 in
Treads5
Lands from deck4 ft 4 1/2 into bottom riser face

Actual rise 3 ft 5 1/8 in Going 10 1/2 in Tread depth 11 1/4 in Angle 33.1° Stringers 3 Tread boards 10

At the landing the ground is 1 1/8 in lower than at the deck, so the real rise is 3 ft 5 1/8 in, not 3 ft 4 in. Same riser count, different riser height.

The deck is more than 30 in above grade. In the IRC that usually means guards on the deck and the open sides of the stair (IRC 2024 R321.1.1; 2021: R312.1.1).

Stair side elevationSide view, drawn to scale: 6 risers of 6 7/8 in and 5 treads with a 10 1/2 in going. Total rise 3 ft 5 1/8 in, total run 4 ft 4 1/2 in, pitch 33.1 degrees. The upper floor forms the top step.R1R2R3R4R5R633.1°going 10 1/2 inriser 6 7/8 intotal run 4 ft 4 1/2 intotal rise 3 ft 5 1/8 indeck height 3 ft 4 indeck surfaceground at landing
To scale, including the ground slope. The rise that matters is measured at the landing, not at the deck.
How this result was calculated
  1. Going from the deck boards2 × 5.5 + 1 × 0.25 gap − 0.75 overhang = 10.5 inThe boards overhang the riser below by the nosing, so the going is the tread depth minus the overhang.
  2. Where the stair landslanding distance = treads × going = 5 × 10.5 = 52.5 inMeasured horizontally from the deck face to the face of the bottom riser.
  3. Ground change at the landing2.08 % × 52.5 = 1.0938 inGround falls away from the deck, so the stair is taller than the deck height.
  4. Actual total risedeck height + ground change = 40 + 1.0938 = 41.0938 in
  5. Risers: smallest count that keeps every riser at or under your maximum at the actual landing pointR = 6; h = 41.0938 ÷ 6 = 6.849 inEach riser count lands the stair at a different spot, so the calculator tests counts from 1 upward and keeps the first that works there.
  6. TreadsT = R − 1 = 5 (the deck is the top step)

Informational checks (IRC 2024 / 2021 values)

Not a compliance decision. Deck stairs follow your locally adopted code.

  • Within referenceRiser height. 6 7/8 in against a reference of at most 7 3/4 in. IRC 2024 R318.7.5.1 (2021: R311.7.5.1)
  • Within referenceTread depth (going, nosing to nosing). 10 1/2 in against a reference minimum of 10 in. IRC 2024 R318.7.5.2 (2021: R311.7.5.2)
  • Within referenceNosing projection. 3/4 in against a reference of 3/4 in to 1 1/4 in. Stairs with open risers may have larger projections under this reference. IRC 2024 R318.7.5.3 (2021: R311.7.5.3)
  • Within referenceRise of a single flight. 41 1/8 in is within the 151 in reference for one flight between floors or landings. IRC 2024 R318.7.3 (2021: R311.7.3)
  • CheckHandrail. 6 risers: this reference calls for a handrail on at least one side of flights with 4 or more risers. Handrail height and grip rules also apply. IRC 2024 R318.7.8 (2021: R311.7.8)
  • CheckUniformity as built. This plan assumes every riser and tread is identical. Finished floors added later change the first and last risers, so plan for the final flooring before cutting. This reference allows at most 3/8 in (9.5 mm) between the largest and smallest riser, and between the largest and smallest tread, in a flight (IRC 2024 R318.7.5.1–.2).
Materials and dimensions (table)
ItemValueNote
Deck height (as measured)3 ft 4 inDeck surface to ground at the deck edge
Actual total rise3 ft 5 1/8 inDeck surface to ground at the landing
Risers6
Riser height≈ 6 7/8 in6.849 in
Treads5
Going10 1/2 in
Landing distance from deck4 ft 4 1/2 inDeck face to bottom riser face
Ground change at landing1 1/8 inLower than at the deck
Stringers3at ≤ 18 in on centre
Deck boards for treads10 pieceseach 36 in long, before overhang
2x12 stringer: first riser cut≈ 5 7/8 inRiser minus tread thickness
2x12 stringer: shortest board5 ft 2 1/8 inBefore trimming allowance

Why deck stairs need their own calculator

Indoors, the floor at the bottom of a stair is level, so the height you measure is the height you build. Outside, it usually is not. Yards slope away from houses for drainage, so the ground where the stair lands is lower than the ground under the deck edge. A stair measured at the deck comes out short: the bottom riser ends up taller than the others, which is exactly the step people trip on.

The trouble is circular. Where the stair lands depends on how many treads it has, and how many treads it needs depends on how high the deck is above the landing. This calculator solves it directly: for each possible riser count it finds the landing point, works out the ground height there, and keeps the fewest risers that respect your maximum at that spot.

Worked example: when the slope adds a step

A deck is 46 1/2 in above the ground at its edge. Treads are two 5 1/2 in deck boards with a 1/4 in gap and a 3/4 in overhang, so the going is 2 × 5.5 + 0.25 − 0.75 = 10.5 in. The maximum riser is 7 3/4 in.

  • On level ground: 46.5 ÷ 7.75 = exactly 6 risers of 7 3/4 in, 5 treads, landing 52 1/2 in from the deck.
  • On ground that falls 2 in over 8 ft: at 52 1/2 in out the ground is 1.09 in lower, so the real rise is 47.59 in, and six risers would be 7.93 in each, over the limit. Seven risers land 63 in out, where the ground is 1.31 in lower: 47.81 in ÷ 7 = 6.83 in per riser.

Measured only at the deck, that stair would have been built with six risers and a bottom step about 1 in taller than the rest. Both cases are automated test fixtures (D3 on the methodology page).

Measuring a deck for stairs

  1. Measure from the top of the decking straight down to the ground at the deck edge where the stair starts.
  2. To find the slope, rest a straight board level on the deck-edge ground (or stretch a level string line) out past where the stair will land, about 6 to 8 ft. Measure down from the board to the ground at the far end: that is the drop over that distance.
  3. If the stair will land on a concrete pad or pavers, enter the pad's height above the ground. The pad top becomes the bottom finished surface.
  4. Then check the landing spot with a tape before you dig footings. The result tells you where the face of the bottom riser lands, measured from the deck face.

For a deeper walkthrough, including indoor stairs, see how to measure total rise.

Deck stair details that are easy to miss

  • Guards and handrails. Under the IRC, flights with four or more risers need a handrail on at least one side (2024 R318.7.8), and open sides more than 30 in above grade within 36 in horizontally need guards (2024 R321.1.1). Section numbers were R311.7.8 and R312.1.1 in the 2021 edition.
  • Bottom landing. The IRC calls for a landing at the bottom of each flight, at least 36 in deep in the direction of travel on a straight run (2024 R318.7.6), with exceptions. A level pad is easier to build to than sloping soil.
  • Stringers. AWC's prescriptive deck guide (DCA 6, 2015) asks for stringers of at least 2x12, three or more when only cut stringers are used, and an intermediate landing when the total height exceeds 12 ft. Use the stringer calculator for cut layout and board length.
  • Bearing at the bottom. The same guide has stringers bear on blocking attached to posts on footings, not simply resting on soil. Footing depth depends on your frost line.

These are references, not your local rules. Many jurisdictions amend the IRC or use their own deck details.

Questions people ask

These are questions Google showed under "People also ask" for related searches (checked 2026-10-24), answered here with the same tested formulas the calculators use.

What is the ideal rise and run for deck stairs?

There is no single ideal, but there are limits and good habits. Where the IRC applies, risers may be at most 7 3/4 in and treads at least 10 in. Two 5 1/2 in deck boards with a 1/4 in gap and a 3/4 in overhang give a 10 1/2 in going, and risers near 7 in make a comfortable outdoor stair. Most important outdoors: make every riser the same, measured at the spot where the stair lands, not at the deck.

How many steps for a 24 inch rise on a deck?

On level ground, 24 ÷ 7.75 = 3.1, so 4 risers of 6 in and 3 treads (the deck is the top step). With 10 1/2 in goings the stair lands 31 1/2 in from the deck. If the ground slopes or a pad is added, enter those in the calculator, because the rise at the landing changes.

How many steps for a 27 inch rise?

4 risers of 6 3/4 in and 3 treads. Three risers would be 9 in each, over the IRC's 7 3/4 in maximum. With 10 1/2 in goings the stair is 31 1/2 in long.

How to build exterior deck stairs?

  1. Measure the deck height and the ground slope where the stair will land; plan a level landing pad.
  2. Plan the stair with the calculator above (risers, treads, landing point) and check it against your local code.
  3. Lay out and cut 2x12 stringers with the stringer calculator, dropping the bottom by the tread thickness.
  4. Attach the stringers to the deck framing with the connection your local rules require, and support the bottom on blocking, posts or a pad as specified.
  5. Fit treads and risers, then add handrails (four or more risers) and guards where the sides are more than 30 in above grade.

Get spans, connections and footings approved locally; this site checks geometry only.