Deck building tool
Deck Stair Calculator
Set out exterior deck steps from one measurement: equal risers, tread run, total run, stringer cut line, framing deductions and IRC code checks — with a live section diagram.
Finished floor to finished floor.
7-7.5in is comfortable; risers are equalised.
Horizontal depth, nosing excluded.
Plumb from the nosing line to the ceiling above.
Landings, stringers & handrail
Half-landings or quarter-turns in this flight.
16in suits most treads; 12in for thin or composite.
Measured above the nosing line.
4in (100mm) sphere rule.
Sets the bottom stringer drop.
Your flight
15 risers × 7.33in
14 treads at 10.50in / 26.7cm · 36.8 degree pitch
- Riser height (equal)
- 7.33in / 18.6cm
- Tread run (going)
- 10.50in / 26.7cm
- Total run
- 147.00in / 373.4cm
- Cut line (diagonal)
- 183.60in / 466.3cm
- Stringer stock length
- 195.60in / 496.8cm (16.3ft)
- Pitch
- 36.8 degrees
- 2R + G
- 25.17in / 63.9cm
- Stringers
- 4 at 12.0in centres (65.2ft stock)
- Handrail length
- 207.60in / 527.3cm (17.3ft)
- Balusters
- 39 at 5.2in centres
Code & comfort checks
IRC (US) allows a maximum 7.75in riser. Every riser in a flight must match within 3/8in.
Minimum going is 10.00in. Shallow treads are the single biggest cause of descending falls.
Comfortable domestic flights sit between 30 and 37 degrees; 42 degrees is the absolute ceiling.
Two risers plus one going should land between 24in and 25in (600-640mm) for a natural stride.
IRC (US) expects at least 36.0in of clear width above the handrail height.
Minimum headroom is 80in measured plumb from the tread nosing line.
IRC wants a graspable handrail 34-38in above the nosing line, continuous for the full flight, and no gap that passes a 4in sphere.
Guidance only — confirm against your local building control before you cut or pour.
Compare riser counts
| Risers | Riser | Going | Run | Pitch |
|---|---|---|---|---|
| 14 | 7.86in | 10.50in | 11.4ft | 38.9° |
| 15 | 7.33in | 10.50in | 12.3ft | 36.8° |
| 16 | 6.88in | 10.50in | 13.1ft | 34.9° |
The highlighted row is your current flight. Nudging the riser count is usually the cheapest way to bring a steep or shallow stair back inside code.
Advanced layout
Mark-out schedule, framing deductions & take-off
Quick answer
How do you calculate deck stairs?
Measure the total rise from the finished ground or landing pad up to the top of the deck boards, divide by a 7 to 7.5in target riser and round to a whole number for the riser count, then divide the rise back by that count for equal risers. Deck steps normally have one fewer tread than risers because the deck surface is the top step. Multiply the tread run by the tread count for total run, take the diagonal for the stringer cut line, drop the bottom of the stringer by one tread thickness and deduct the top riser at the rim joist.
- Total rise runs from the ground pad to the top of the deck boards.
- Risers = rise divided by a 7-7.5in target, rounded to a whole number.
- Treads = risers minus one, because the deck surface is the top step.
- Total run = tread run x tread count; 10.5in or two 5/4 boards is typical.
- Stringer cut line = sqrt(rise squared + run squared), plus waste.
- Drop the bottom stringer by one tread thickness and deduct the top riser.
Measuring total rise on a deck
Deck stairs go wrong at the bottom, not the top. Stretch a straight edge out from the deck surface, level it, and drop a tape from its underside to the finished landing surface. Include the paving, slab or gravel that will be there when the job is done. That figure — deck boards to finished ground — is what the calculator wants as total rise.
| Total rise | Risers | Riser height | Treads | Total run at 10.5in |
|---|---|---|---|---|
| 24in / 610mm | 3 | 8.00in | 2 | 21in |
| 36in / 914mm | 5 | 7.20in | 4 | 42in |
| 48in / 1219mm | 7 | 6.86in | 6 | 63in |
| 57in / 1448mm | 8 | 7.13in | 7 | 73.5in |
| 72in / 1829mm | 10 | 7.20in | 9 | 94.5in |
Know your numbers in 30 seconds
Enter your step count, tread depth and riser height — the stair runner calculator gives you the exact length to order, in metres and feet, with waste included.
Open the stair runner calculatorTread material sets the run and the spacing
Two 5/4x6 deck boards with a 1/4in gap give a 10.5in run, which is why that number appears on almost every deck plan. Composite treads change the picture twice over: they need closer stringer spacing, and many systems come with a matched stair-nose profile that alters the effective run. Check the manufacturer's stair span table before you buy — over-spanned stringers void the tread warranty.
- 2x solid timber: spans 24in on centre, cheapest, needs annual sealing on cut ends.
- 5/4 decking: 16in on centre, the default for pressure-treated decks.
- Composite: 12in on centre, use the maker's stair-nose profile for the nosing.
- Seal every cut face — raw end grain is where deck stringers rot first.
The two deductions that keep risers equal
Drop the bottom of the stringer by one tread thickness so the first riser matches the rest, and deduct one riser height at the top when the deck surface acts as the top step. Both figures come out of the advanced layout panel for the exact tread you are using, alongside a mark-out schedule that gives the height and run for every step so you can check the cut before the saw comes out.
Guards and handrails
Any flight with four or more risers needs a graspable handrail, and open sides need a guard 34-38in above the nosing line. Work that into the post layout before you fix the stringers, not after.
Whatever you decide, get the numbers first: the stair runner calculator doubles as a stair runner length calculator, adding nosing wrap, landings, winders, pattern repeat and waste so you order the right length the first time.
Frequently asked questions
How do I calculate deck stairs from the ground?
Run a level line out from the deck surface to a point above where the bottom step will land, then measure straight down to the finished ground or concrete pad. That vertical figure is your total rise — measuring to raw soil that will later be paved is the most common cause of a first step that ends up too tall.
How many stringers do deck stairs need?
Spacing is set by the tread material, not the width. Solid 2x timber spans 24in, 5/4 decking wants 16in and most composite decking makers specify 12in on stairs because composite loses stiffness on a diagonal span. A 36in wide stair with composite treads needs four stringers. The stair stringer calculator returns the count and throat depth.
What is the standard deck step rise and run?
A 7 to 7.5in rise with a 10.5in run is the standard, because 10.5in is exactly two 5/4x6 deck boards with a small gap between them. The IRC caps the riser at 7 3/4in for residential stairs and requires a 10in minimum run.
Why do you drop the bottom of a deck stringer?
Because the tread sits on top of the notch. Without dropping the stringer by one tread thickness, the first step ends up one board thicker than every other riser, which breaks the 3/8in equal-riser tolerance. The advanced panel returns the exact drop for your tread thickness.
Do deck stairs need a landing pad?
Yes. Stairs must land on a firm, level surface at least 36in deep in the direction of travel. Pouring that pad first, then measuring the rise to it, keeps the flight equal — retro-fitting a pad under finished stairs always shortens the bottom riser.
Is the deck stair calculator free?
The geometry, diagram and code checks are free with no account. The advanced layout — mark-out schedule, bottom stringer drop, top framing deduction and take-off — needs a free account, and it is also available inside the Riser portal where flights save to a project and become quotes.