Finished surface to finished surface (deck boards included)
Code max 7-3/4". 7" to 7-1/2" is comfortable.
3/4"-1-1/4" required when the run is under 11"
Minimum 36" (IRC)
Deck or floor is the top step. Most common.
Stringer length
6' 9-5/8"
Buy 3 × 8' 2x12s
7 risers at 6-7/8" · 6 treads at 11"
Mark the stringer
Stair layout
Side view, drawn to scale
Laying out the stringer on the 2x12
Mark notch 1 at 3-13/16" from the bottom end, then measure every notch from that first mark (don't add up one step at a time):
Cutting the stringer (bottom two steps, close up)
Cut it in this order
- 1Sight down the 2x12 and put the crown (the hump) up. The notches go on that edge.
- 2Clamp stair gauges on your framing square: 6-7/8" on the tongue (rise), 11" on the blade (run).
- 3Mark 6 notches along the edge. Measure each one from the first mark using the list, so small errors don't add up.
- 4Mark the floor cut (level) at the bottom and the plumb cut at the top.
- 5Cut the first rise 1-1/2" short (5-3/8"), the tread thickness, so every finished step is 6-7/8".
- 6Cut the notches with a circular saw, stop at the inside corners and finish with a handsaw or jigsaw.
- 7Test-fit this stringer, then use it as the pattern for the other 2.
How the numbers are worked out
- 1
How many risers
48 ÷ 7.25 = 6.62 → 7 risers
- 2
Exact riser height
48 ÷ 7 = 6.857" → 6-7/8"Stepping off 6-7/8" 7 times is 1/8" long. Mark the heights below instead.
- 3
Treads
7 − 1 = 6 (the deck is the top step)
- 4
Total run
6 × 11 = 5' 6"
- 5
Stringer length
√(48² + 66²) = 6' 9-5/8". The cut stringer fits in 6' 9" of board; with 2" to trim, buy 8'.
- 6
First rise cut (stringer drop)
6.86 − 1.5 tread = 5-3/8"
- 7
Throat
11-1/4" − 5.82 notch depth = 5-7/16" (5" or more is the target)
Story pole: top of each tread from the ground
IRC code checks
Rules of thumb (not code)
Material list
Estimated cost
Lumber and hangers at September 2026 retail prices (sources below). Labor is a rough hour allowance at $50-$125/hr, a typical carpenter/handyman billing rate. Riser boards not priced. Your yard and crew will differ.
Free to use. No signup needed.
Last updated: 2026-09-24
How to Calculate Stair Stringers, Risers, and Treads
I've been a carpenter for over 20 years. Stair math is straightforward, but it's the kind of thing where one bad measurement wastes an entire 2x12. This calculator does the layout for you. Plug in your total rise, and it gives you the riser count, actual riser height, tread layout, stringer length, material list, and a cost breakdown.
The number one mistake I see: measuring the total rise wrong. You need the exact distance from finished floor to finished floor (or finished floor to deck surface). Not rough framing. Not subfloor to subfloor. Off by half an inch on total rise and every single riser is off. That is how you end up with a trip hazard at the top or bottom step, and that is how you fail inspection.
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Inputs you'll need
- Total rise - Vertical distance from finished lower floor to finished upper floor or deck surface (inches)
- Target riser height - 7-3/4" code maximum; 7" to 7-1/2" is comfortable
- Tread run - Nosing to nosing, horizontal (10" minimum per IRC)
- Nosing - 3/4" to 1-1/4", required when the run is under 11"
- Stair width - Side to side measurement (36" minimum residential)
- Riser boards - Closed or open risers (open risers more than 30" up must not pass a 4" ball)
- Tread material - Sets tread thickness (for the stringer drop), boards per tread, and cost
IRC Code Requirements at a Glance
| Requirement | IRC Limit | Practical Target |
|---|---|---|
| Max riser height | 7.75" | 7" - 7.5" |
| Min tread depth | 10" | 11" |
| Riser variation | Max 3/8" between any two | Consistent throughout |
| Min stair width | 36" clear | 36" - 42" |
| Headroom | 6'-8" minimum | 7'+ preferred |
| Stringer throat depth | No IRC number | About 5"+ on a cut 2x12 (AWC DCA 6 basis) |
Worked examples
Example A: Deck stairs, 48" rise (4 ft deck), 11" treads, 3 stringers
- 48" / 7.25" target = 6.6, round to 7 risers
- Actual riser height = 48 / 7 = 6.86"
- Treads = 7 - 1 = 6
- Total run = 6 x 11" = 66" (5.5 ft)
- Stringer length = sqrt(48² + 66²) = sqrt(2304 + 4356) = 81.6" = 6.8 ft (order 8-ft boards)
- Stair angle = atan(48/66) = 36°
- 7-11 check: 6.86 + 11 = 17.86" ✓
Example B: Interior stairs, 108" rise (8 ft ceiling plus a 12" floor system), 11" treads, 3 stringers
- 108" / 7.25" = 14.9, round to 15 risers
- Actual riser height = 108 / 15 = 7.2"
- Treads = 14
- Total run = 14 x 11 = 154" (12.8 ft)
- Stringer length = sqrt(108² + 154²) = sqrt(11664 + 23716) = 188.1" = 15.7 ft (order 16-ft boards)
- Stair angle = atan(108/154) = 35°
Example C: High deck, 72" rise, 10.5" treads (needs mid-span support)
- 72 / 7.25 = 9.93, round to 10 risers
- Actual riser = 72 / 10 = 7.2"
- Treads = 9, total run = 94.5" (7.9 ft)
- Stringer length = sqrt(72² + 94.5²) = sqrt(5184 + 8930) = 118.8" = 9.9 ft. The cut stringer needs about 118-1/4" of board, which leaves no room to trim a 10-foot (120"), so order 12-ft boards
- The run is 94.5", more than the 6'-0" the AWC deck guide allows for cut stringers. Set a 4x4 post on a footing under the stringers, add a landing, or use solid stringers.
Building a deck? Use our deck cost calculator for the full framing and decking estimate, or the joist span calculator for framing layout. For stair railing materials, use the deck railing calculator.
Mistakes that burn you on stair layout
- Measuring to the subfloor instead of the finished floor. If you lay out subfloor to subfloor and the upper floor later gets 3/4" hardwood while the lower floor gets 1/2" tile, the error doesn't spread out: the top step ends up 3/4" taller and the bottom step 1/2" shorter than the rest, both past the 3/8" riser variation the IRC allows.
- Forgetting the bottom riser drop. You have to subtract one tread thickness from the bottom of every stringer. Skip this and the first step is noticeably taller than the rest.
- Over-cutting the notches with a circular saw. The blade arc cuts past the corner and weakens the stringer throat. Always stop short and finish with a jigsaw or handsaw. A cracked stringer under load is a serious safety problem.
- Using 2x10 for notched stringers. Once you cut the notches there is too little wood left, and the AWC deck guide calls for 2x12 stringers. Always use 2x12.
- Not checking the framing square. A framing square that is off by even 1/16" compounds across 14 steps. Check your square against a known straight edge before layout.
Lumber prices per linear foot (checked September 2026)
| Material | Cost per LF | Best For |
|---|---|---|
| PT 2x12 (stringer) | $2.10 - $3.40 | Exterior/deck stairs |
| PT 5/4x6 deck boards (2-3 per tread) | $0.90 - $1.40 | Deck treads |
| Composite deck boards (2-3 per tread) | $2.60 - $5.50 | Low-maintenance decks |
| Cedar 5/4x6 (2-3 per tread) | $2.40 - $4.50 | Natural look, moderate durability |
| Oak stair treads (1 per tread) | $11.00 - $19.00 | Interior finished stairs |
Stairs are one of those things that look simple until you mess up the layout. I always cut a test stringer first and set it in place before cutting the rest. One wrong mark on the pattern wastes three 16-foot 2x12s. At about $48 each, that is roughly $145 in lumber for a careless mistake. Measure twice, cut once applies more to stairs than almost anything else on the jobsite.
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Sources
- International Code Council, 2021 IRC R311.7 Stairways. Your jurisdiction may amend these; check your local code.
- American Wood Council, DCA 6 Prescriptive Residential Wood Deck Construction Guide (stair stringers: 2x12 minimum, at least three cut stringers, 18" max spacing, span limits)
- Home Depot, 2x12x16 #2 ground-contact pressure-treated lumber listing (price checked September 2026)
- Tread and hardware prices, checked September 2026 (local prices vary): PT 5/4x6x16, cedar 5/4x6x16, Trex Enhance 16 ft, red oak tread 48 in, Simpson LSC stringer connector. Labor uses a $50-$125/hr carpenter/handyman billing range; the hours are a rough allowance.
How to Use This Calculator
Measure your total rise
Measure the vertical distance from the finished lower floor to the finished upper floor or deck surface. Use a level and tape measure for accuracy. This is the single most important number in stair layout.
Select tread depth and stair width
Choose your tread depth (10" minimum per IRC, 11" is standard) and set your stair width. Most residential stairs are 36" wide minimum. Wider stairs or decks may need extra stringers.
Choose tread material and riser boards
Choose your tread material (it sets the tread thickness for the stringer drop) and whether the stair has riser boards. The calculator sizes the stringer count: at least three cut stringers, no more than 18" apart.
Review layout and code compliance
Check the framing square settings, the first rise cut, and the code checks. Adjust your inputs until the layout passes before you cut.
Stair Stringer Layout Formulas
Number of Risers = Total Rise ÷ Target Riser Height, rounded to the nearest whole number
(if that makes a riser taller than 7-3/4", use one more riser)
Actual Riser Height = Total Rise ÷ Number of Risers
Number of Treads = Number of Risers − 1 (one step down), or = Number of Risers (flush top)
Total Run = Number of Treads × Tread Run
Stringer Length = √(Total Rise² + Total Run²)
First Rise Cut = Riser Height − Tread Thickness
Throat = 11-1/4" − (Riser × Run ÷ √(Riser² + Run²))
Stair Angle = arctan(Total Rise ÷ Total Run)Where:
- Total Rise
- = Vertical distance from finished lower floor to finished upper floor (inches)
- Tread Depth
- = Front-to-back dimension of each step (10" min per IRC, 11" standard)
- Total Run
- = Horizontal distance from the face of the first riser to the face of the last
- Stringer Length
- = Diagonal length of the stringer board before notching
- Stair Angle
- = Angle of the stairway from horizontal (30-37° is comfortable)
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Frequently Asked Questions
How do I calculate stair stringers?
Start with your total rise (floor to floor, in inches). Divide by your target riser height (7" to 7.5" is ideal) to get the number of risers. Round to the nearest whole number. The actual riser height is total rise divided by that number. Treads = risers minus 1. Total run = treads times tread depth. Stringer length = square root of (total rise squared + total run squared). For a 9-ft (108") rise with 11" treads, you get 15 risers, 14 treads, a total run of 154", and a stringer length of about 15.7 ft.
What is the maximum riser height allowed by code?
The International Residential Code (IRC) sets the maximum riser height at 7.75 inches (7-3/4"). The practical sweet spot is 7" to 7.5" per riser. Risers in a single stairway cannot vary by more than 3/8" from tallest to shortest, so accurate measurement and layout are critical. If your rise calculation gives you risers over 7.75", add one more riser to bring the height under the limit.
How many stair stringers do I need?
The American Wood Council deck guide (DCA 6) calls for at least three cut stringers, no more than 18" apart. That is 3 for a 36" stair and 4 for 48". Composite and PVC treads often need closer support, so check the manufacturer's stair span before you space stringers.
What size lumber do I use for stair stringers?
2x12 is the standard for stair stringers. After you cut the notches for treads and risers, check the solid wood left below the deepest notch (the "throat"). The IRC does not set a number; the American Wood Council deck guide (DCA 6) requires 2x12 stringers and was engineered assuming about 5" of wood left below the notches. A 7-1/4" rise with an 11" run leaves about 5-3/16" on a 2x12 (11-1/4" actual). A notched 2x10 leaves too little.
What is the 7-11 rule for stairs?
The 7-11 rule is a comfort guideline: riser height + tread depth should equal 17 to 18 inches. A 7" riser with an 11" tread gives you 18" - right in the sweet spot. Stairs that fall outside this range feel either too steep (riser too tall, tread too shallow) or too shallow and sprawling (riser too short, tread too deep). The IRC minimum tread depth is 10", and the max riser is 7.75", so the code range naturally overlaps with this rule.
How much does it cost to build stairs in 2026?
It depends mostly on tread material, the number of steps and your labor rate. The calculator above prices the stringers, treads, risers and hardware per foot of lumber and labor per hour, adjusted for your location, so use it with your real numbers. As a reference point, a 16-foot pressure-treated 2x12 listed at about $48 at Home Depot in September 2026.
How do I cut a stair stringer?
Mark the stringer with a framing square using stair gauges set to your riser height and tread depth. Draw the first riser line, then walk the square down the board marking each step. Important: subtract one tread thickness from the bottom riser so the first step equals all the others once the treads are installed. Cut the notches with a circular saw, but stop short of the inside corner. Finish the cut with a handsaw or jigsaw to avoid over-cutting, which weakens the stringer. Always cut a test stringer first and check it in place before cutting the rest.
What is the minimum stair width?
The IRC (R311.7.1) requires at least 36 inches of clear width above handrail height. Handrails may project up to 4-1/2" on each side, so at and below handrail height the clear width can be 31-1/2" with one handrail or 27" with two. Deck stairs follow the same rule unless your local code differs.
Do I need to adjust the bottom riser for tread thickness?
Yes. Drop the stringers by the thickness of one tread at the bottom. If you are using 5/4 deck boards (1" actual) or 2x treads (1.5" actual), cut that amount off the bottom of each stringer. Without this adjustment, the first riser will be taller than the rest by the tread thickness, which violates the 3/8" variance rule and will feel wrong underfoot. It is an easy one to miss.
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