How to Build Stairs

Updated September 2026 · Home Project Resources

Measure the total rise first, from the finished surface at the bottom to the finished surface at the top, then divide it into equal risers. Every other number in the project follows from that one measurement. Unequal risers are both the most common mistake in stair building and the one that fails inspection.

The reason is that people walking a staircase stop looking after the second or third step. Your legs learn the rhythm and then repeat it. A riser that is half an inch off breaks that rhythm at exactly the moment your eyes are somewhere else, and that is how people fall.

Need the numbers worked out? Our stair calculator takes your total rise and gives you riser count, riser height, tread depth, total run, and stringer length.

Updated September 2026

A note on numbers. This page gives you rise, run, tolerances, code limits and a full cut list, not dollar figures. Lumber moves with the market, railing systems vary enormously by material, and stair labor is quoted per step by local carpenters. Work out your exact flight here, then price that cut list at a lumberyard and against three quotes.

How to build stairs, step by step

1. Measure the total rise from finished floor to finished floor, in inches.
2. Divide by 7 and round to a whole number to get your riser count.
3. Divide total rise by that riser count to get the exact riser height.
4. Pick a tread depth that passes the comfort formulas and the local minimum.
5. Multiply tread depth by the number of treads for the total run.
6. Check headroom and landing space against the run you just calculated.
7. Lay out the stringer with a framing square and stair gauges.
8. Drop the bottom cut by exactly one tread thickness.
9. Cut the first stringer, then test fit it before cutting the rest.
10. Attach the stringers at the top and anchor them at the bottom.
11. Install risers first, then treads, working from the bottom up.
12. Add the handrail and guards to the required heights.

A straight flight of exterior stairs is a solid weekend for two people once the landing pad has cured. The layout and the first stringer take most of the first day.

The code numbers, and who the authority actually is

These are the values used in the International Residential Code, which most US jurisdictions adopt in some form. Your local building department is the authority, and amendments are common, so verify before you cut anything.

The 3/8 inch rule is worth stating on its own, because it is the one that catches people. The difference between the tallest riser and the shortest riser in a single flight cannot exceed 3/8 inch. Not 3/8 inch from the average, the total spread across the whole flight. Inspectors measure it, and a flight that fails gets torn out.

That is also why the bottom cut adjustment further down this page matters so much. Forgetting it makes the bottom riser off by one tread thickness, typically 1 1/2 inches, which is four times the allowed variation.

Anything structural inside a house, and most exterior stairs attached to a deck, needs a permit. If your stairs are part of a deck, they get inspected with it.

Total rise, riser count, and why you divide

Measure total rise correctly. Finished surface to finished surface. If you are going to add 3/4 inch hardwood at the top or a 1 1/2 inch concrete topping at the bottom later, include it now. Measure at both ends of where the stairs will land, because floors and pads are rarely dead level, and use the larger number.

Divide by 7 to get a starting riser count. Seven inches is a comfortable riser, so total rise divided by 7 gives you roughly how many steps you want. Round to the nearest whole number.

Divide total rise by that whole number to get the exact riser height. That number will almost never be a round fraction, and that is fine. It just has to be under the maximum and the same all the way up.

Treads are always one fewer than risers on a standard flight, because the top landing serves as the last tread. This trips people up constantly. Sixteen risers gives you fifteen treads.

Total run equals the number of treads times the tread depth. Check that against the space you have before you go further, because run is where the surprise usually is. A tall flight needs a lot of floor. Once the flight is built and you are covering it, how to measure stairs for carpet converts the same rise and run into yardage.

The comfort formulas, as a cross-check

Two old rules of thumb have survived because they work. Use them to sanity check a combination that technically passes code but feels wrong.

2R plus T should land around 24 to 25 inches. Two times the riser plus the tread depth. This one is based on the length of an average stride, and stairs that hit it feel natural at a normal walking pace.

R plus T should land around 17 to 18 inches. Riser plus tread. A simpler check that gets you to the same place.

Run both. A 7 inch riser with an 11 inch tread gives 25 and 18, which is a comfortable staircase. A 7 3/4 inch riser with a 10 inch tread gives 25.5 and 17.75, which is legal and noticeably steeper. A 5 inch riser with a 16 inch tread gives 26 and 21, which is technically shallow enough for anyone but feels like a ramp and makes people stutter step.

The tradeoff is always the same. Taller risers mean fewer steps and less total run, which saves space. Shallower risers are easier to climb but eat floor area fast.

Cutting stringers

A stringer is the sawtooth board that carries the treads. Cutting the first one is the part of the job people dread, and it is not hard once the layout makes sense.

Material. Use 2x12 stock. A 2x10 does not leave enough wood behind the notches once you cut a 7 inch rise and a 10 inch tread out of it. What remains behind the cuts is called the throat, and you want at least 5 inches of it. Less than that and the stringer flexes or splits.

For exterior stairs, use pressure treated lumber rated for ground contact on anything within 6 inches of soil, and rated for above ground use elsewhere. Our board feet calculator converts your cut list into board feet for pricing.

Lay out with a framing square and stair gauges. Stair gauges are small brass clamps that fix onto the square. Set one on the tongue at your riser height and one on the blade at your tread depth. Now the square becomes a template you can walk down the board, and every notch comes out identical.

Clamp the gauges tight and check them against a tape after the first two or three steps. A gauge that has slipped 1/16 inch gives you a flight that is a quarter inch off by the top.

Start at one end, seat both gauges against the top edge of the board, and trace the notch. Slide the square down so the heel of the last tread line meets the toe of the next riser line, and trace again. Repeat for the full riser count. Then mark the top plumb cut and the bottom level cut.

Cut with a circular saw and finish with a handsaw. Stop the circular saw exactly at the corner of each notch. Do not overcut through the corner, because that kerf runs into the throat and weakens the stringer at its narrowest point. Finish the last half inch of each cut with a handsaw or a jigsaw.

Test fit the first stringer before cutting the other two. Set it in place, check the bottom sits flat on the pad, check the top plumb cut sits tight to the framing, and check a level laid across a couple of notches. Fix the layout now, not after you have cut three boards.

The bottom cut adjustment, and why it exists

This is the step that gets forgotten, so here is exactly what is happening.

When you lay out a stringer with a framing square, every notch is identical. The vertical leg of each notch equals your riser height. That is correct for the middle of the flight, because each tread sits on top of a horizontal cut, and every riser is measured from the top of one tread to the top of the next. Each one gains the tread thickness, so they all stay equal.

The bottom is different. The bottom of the stringer sits directly on the pad or the floor. There is no tread underneath it. So the first riser, measured from the ground to the top of the first tread, comes out as your riser height plus the tread thickness.

With 1 1/2 inch treads, that first step is 1 1/2 inches taller than every other step. That is four times the allowed 3/8 inch variation, and it is exactly the step people trip on because it is the one they take at full walking speed.

The fix. Cut the bottom of the stringer shorter by exactly the finished tread thickness. If your treads are 1 1/2 inch 2x material, drop the bottom cut 1 1/2 inches. If the treads are 1 inch composite, drop it 1 inch. Measure the actual tread stock rather than trusting the nominal size, because a 2x6 is 1 1/2 inches but a 5/4 deck board is more like 1 inch.

One more correction at the bottom. If the stringer sits on a concrete pad and the treads are the finished walking surface, that is all you need. If there will be a finished floor or a paver surface added under the stringer later, subtract that thickness too, or the whole flight shifts.

Stringer spacing, material, and the center stringer

The rule people remember is stringers at 16 inches on center, and that is a safe default. Thinner tread material needs tighter spacing. 5/4 deck boards spanning 24 inches between stringers will feel springy underfoot within a year, and springy stairs make people nervous even when they are structurally fine.

A 36 inch wide flight with two outer stringers and nothing in the middle has a 33 inch clear span. That is too much for almost any tread material, so add the center stringer. It is one more board and it is the cheapest confidence you will buy on the whole project.

Attaching top and bottom

At the top. The usual method is to hang the stringers off a rim joist or a header. Attach a ledger to the back of the plumb cut, or use metal stringer hangers, which are purpose built connectors that transfer the load properly. Toe nailing stringers into a rim joist is common and it is not adequate on its own for an exterior flight. Use structural screws or hangers rated for the load, and use hot dip galvanized or stainless hardware anywhere outdoors, because the copper in modern pressure treated lumber corrodes plain steel fast.

At the bottom. Exterior stairs should land on a concrete pad, not on dirt or gravel. Wood sitting on soil wicks moisture, rots, and shifts, and a stringer that settles half an inch throws the bottom riser out of tolerance. Pour a pad at least 4 inches thick, extending 3 to 6 inches beyond the stairs in every direction, sloped slightly away from the house. Our concrete calculator handles the volume.

Anchor the stringers to the pad with a treated 2x4 kick plate bolted down with concrete anchors, or with metal angle brackets. Without an anchor, the base of a stair flight walks forward over time as people push off going up.

Landings. If the flight exceeds the maximum vertical rise between landings, typically 12 feet, you need an intermediate landing. A landing must be at least as deep as the stair is wide, so a 36 inch stair needs a 36 inch minimum landing depth. Doors that swing over a landing have their own rules.

Treads, risers, and nosing

Install risers first if you are using them, then treads, working bottom to top.

Closed risers are the vertical boards that fill the back of each step. Interior stairs almost always have them, and code limits the opening on open riser stairs so that a 4 inch sphere cannot pass through, which effectively means exterior stairs with open risers need the gap kept small or the flight kept low.

Treads. Two 2x6 deck boards make a 11 inch tread with a small drainage gap between them, which is why that combination is so common on decks. Interior treads are typically 1 inch or 1 1/16 inch hardwood stair tread stock, or 3/4 inch plywood under carpet.

Leave a 1/8 to 1/4 inch drainage gap between exterior tread boards. Water that sits on a tread is what rots it and what freezes into an ice patch.

Nosing is the overhang of the tread past the riser below it. Where the tread depth is under 11 inches, code requires a nosing of 3/4 to 1 1/4 inches, and the nosing has to be consistent within 3/8 inch across the flight. It exists because it gives the ball of your foot a little more landing area on the way down without adding to the total run.

Fasten treads with two screws per stringer, predrilled near the ends of the board to keep it from splitting. Countersink so nothing catches a shoe.

Handrails and guards

Handrails are required on at least one side of any flight with four or more risers. Height is measured vertically from the nosing line, and the typical range is 34 to 38 inches. The rail has to be continuous for the full flight, and it has to return to the wall or the post at each end rather than ending in a stub that catches a sleeve.

Graspability is a real requirement, not a preference. A round rail between 1 1/4 and 2 inches in diameter qualifies as a Type I handrail. A non circular Type I rail needs a perimeter of 4 to 6 1/4 inches and a maximum cross section of 2 1/4 inches. Type II rails, which are larger, need a specific finger recess profile.

The practical translation: a 2x4 laid flat on top of posts is not a handrail. It is far too wide to grab, and it fails inspection routinely. Buy actual handrail stock.

There has to be at least 1 1/2 inches of clearance between the rail and any wall behind it so your hand can wrap around.

Guards are the barrier that stops a fall off the open side. Required where the walking surface is more than 30 inches above the surface below, at a minimum height of 36 inches in residential work. Openings must reject a 4 inch sphere, though on the open triangular area formed by a stair tread, riser, and the guard bottom rail, the allowance is a 6 inch sphere.

Exterior stairs are different

Lumber. Everything must be pressure treated, and the treatment rating matters. Ground contact rated material for stringers and anything within 6 inches of soil, above ground rated for treads and rails. Cut ends should get a brush coat of copper naphthenate preservative, because the cut face is untreated wood.

Hardware. Hot dip galvanized at minimum, stainless in coastal or high moisture areas. Modern treated lumber is corrosive to plain and electroplated steel, and fasteners that fail are hard to spot until a tread lets go.

Drainage. Gap the treads, slope the pad away from the house, and keep the bottom of the stringers off the soil. Water is what kills exterior stairs, always.

Older homes. If you are demolishing existing stairs in a home built before 1978, assume the paint contains lead until tested, and follow lead safe work practices. Sanding or dry scraping old painted stairs generates lead dust that is genuinely hazardous to children. If you find suspect insulation, sheet flooring, or mastic in a pre-1990 building, do not disturb it, and get it tested for asbestos before demolition.

Worked example: a 108 inch total rise

Say your deck surface is 108 inches above the finished patio, which is a 9 foot rise.

Riser count. 108 divided by 7 equals 15.43. Round to 16.

Riser height. 108 divided by 16 equals 6.75 inches exactly. Comfortably under the 7 3/4 inch maximum, and it works out clean.

Tread count. 16 risers minus 1 equals 15 treads, because the deck surface is the sixteenth walking surface.

Tread depth. Two 2x6 deck boards laid with a 1/8 inch gap gives 11 1/8 inches. Call it 11 inches of run per tread, which is over the 10 inch minimum and gets you out of the mandatory nosing requirement.

Comfort check. 2R plus T equals 13.5 plus 11, which is 24.5. Right in the target range. R plus T equals 6.75 plus 11, which is 17.75. Also right in range. This flight will feel good.

Total run. 15 treads times 11 inches equals 165 inches, which is 13 feet 9 inches. Confirm you have that much space in front of the deck plus a landing area at the bottom.

Stringer length. The diagonal is the square root of 108 squared plus 165 squared, which is the square root of 38,889, or about 197.2 inches. That is 16 feet 5 inches, so you need 2x12 stock at least 18 feet long, and 20 foot boards are the common stock length. Order 3 of them for a 36 inch wide flight.

Bottom cut. Treads are 1 1/2 inch 2x6 material, so drop the bottom cut on every stringer by exactly 1 1/2 inches.

Material list. - 3 pieces of 20 foot pressure treated 2x12 for the stringers, which is 120 board feet - 30 pieces of 3 foot 2x6 treated decking for the treads, or 90 linear feet, which is 90 board feet - 16 pieces of 3 foot riser stock if closing the risers - Stringer hangers or a ledger with structural screws - One treated 2x4 kick plate and 4 concrete anchors - Handrail stock, posts, and balusters for 16 feet of rail - Concrete for a landing pad 4 feet by 4 feet by 4 inches, which is 5.33 cubic feet, or 0.2 cubic yards, about 10 bags of 80 pound mix

Pricing the materials. The list above is the whole order, so hand it to the lumberyard as it stands and you have a real number the same day. Two lines move that number more than everything else put together. The railing is the first: handrail stock, posts and balusters swing further between plain treated lumber and a composite or metal baluster system than the rest of the list swings in total. The tread material is the second, since treated decking, cedar and composite are three quite different orders for the same 16 treads. Stringers, hardware, anchors and the bags for the pad barely move at all.

Labor, separately. A contractor building an exterior flight this size normally quotes it per step, which makes bids easy to compare once you have settled your step count. A landing or a turn adds more than the extra steps suggest, because both mean extra framing and a second set of stringers. Interior stairs with finished hardwood treads and a full railing system sit in a different bracket entirely, since the finish carpentry is most of the job. Give every bidder the same rise, run and step count from the calculator so you are pricing one flight three times rather than three different flights.

Run your own numbers through the stair calculator, size the lumber with the board feet calculator, and if the stairs are part of a larger project, the deck calculator and our how to build a deck guide cover the framing they attach to.

Frequently asked questions

What is the maximum riser height for stairs?

7 3/4 inches under the International Residential Code, which most US jurisdictions adopt. Commercial stairs are typically limited to 7 inches. Your local building department can amend these, so confirm the number for your area before cutting stringers, especially if you are trying to fit a tall rise into a short run.

How many stringers do I need for stairs?

Three for a standard 36 inch wide flight, spaced no more than 16 inches on center. Four for anything 42 to 48 inches wide. Two stringers leaves a 33 inch clear span between them, which is too far for 2x tread material and much too far for 5/4 decking. The center stringer is the cheapest insurance on the whole build.

Why do you cut the bottom of a stair stringer shorter?

Because the bottom of the stringer sits directly on the ground with no tread beneath it, while every other notch gets a tread stacked on top. Without the adjustment, the first riser ends up taller than the rest by exactly the tread thickness, usually 1 1/2 inches. That is four times the 3/8 inch variation allowed in a flight, and it fails inspection.

How much can stair risers vary?

3/8 inch between the largest and smallest riser in a single flight, and the same limit applies to tread depth. That is the total spread across the whole flight, not the deviation from an average. Inspectors measure it because uneven risers are a genuine fall hazard once your legs have learned the rhythm.

What is the ideal rise and run for stairs?

A riser around 7 inches with a tread around 11 inches is close to ideal for most people. Check any combination against 2R plus T, which should land between 24 and 25 inches, and R plus T, which should land between 17 and 18. Both formulas come from average stride length, and combinations that miss them feel wrong even when they pass code.

How deep does a stair landing need to be?

At least as deep as the stairway is wide, so a 36 inch wide flight needs a landing at least 36 inches deep. A landing is also required to break up any flight exceeding roughly 12 feet of vertical rise. Doors opening onto a landing add further requirements, so check with your building department.

Do deck stairs need a concrete pad?

Yes, in practice. Stringers landing on soil or loose gravel wick moisture and rot, and they settle unevenly, which throws the bottom riser out of the 3/8 inch tolerance. A 4 inch pad extending a few inches past the stairs on every side, sloped away from the house, solves both problems. Anchor the stringers to it with a treated kick plate.

How much does it cost to build stairs?

Build the materials list first, since that half you can price yourself: stringers, treads, risers, hardware, railing and a landing pad for however many steps your rise works out to. Take that list to a lumberyard and the material side is settled in an afternoon, and the railing and tread choices will move it more than anything else on it. Contractor labor is quoted separately and usually per step, so the step count from the calculator is the number that makes bids comparable. Interior stairs with finished hardwood treads and a full railing system cost considerably more than an exterior flight of the same size, because the finish carpentry is most of the work. Get three local quotes against one written scope.

The short version

Measure total rise from finished surface to finished surface. Divide by 7, round to a whole number, then divide the rise by that number for an exact riser height that repeats all the way up. Treads are always one fewer than risers.

Pick a tread depth that clears the 10 inch minimum and passes 2R plus T of 24 to 25 inches. Multiply by the tread count for the total run and confirm you have the space.

Lay out the stringers with a framing square and stair gauges, cut with a circular saw and finish the corners by hand, and drop the bottom cut by exactly one tread thickness. Test fit the first stringer before cutting the other two.

Hang the top with hangers or a ledger, anchor the bottom to a concrete pad, use three stringers on a 36 inch flight, and put a real graspable handrail on it at 34 to 38 inches. Outdoors, everything is treated lumber with hot dip galvanized hardware and gaps for drainage.

Our stair calculator does the rise and run math, the board feet calculator prices the lumber, and the how to build a deck guide covers the structure at the top of the flight.