Stair Stringer Calculator

How to use it

1. Enter the total rise from the finished surface at the bottom to the finished surface at the top, and the tallest riser you want. The calculator takes the fewest risers that stay at or under it and divides the rise evenly.
2. Set the run and nosing. The run is the depth of each tread cut, measured nosing to nosing; the tread board is the run plus the nosing deep.
3. Pick the materials: tread and riser thickness (0 for open risers), stringer stock, and how the top and bottom are built. The tread thickness sets how much comes off the bottom of the stringer.
4. Check the results, then print the page or download the full-size template. The share link and this browser keep your numbers.

How to measure total rise

Total rise is the vertical distance from the finished surface the stair starts on to the finished surface it arrives at. Indoors, measure in the stairwell from the finished lower floor to the finished upper floor. If flooring isn't down yet, measure between the subfloors, add the flooring still to come at the top and subtract the flooring still to come at the bottom, so the number is finished floor to finished floor; then choose "On a subfloor" at the bottom so the calculator allows for flooring laid around the foot. Floors are rarely dead level, so measure at both sides of the stair and use the average.

For a deck, the rise is not the height of the deck where you stand; it is the height above the spot where the bottom step will land. Run a straight board or a string with a line level out from the deck surface past where the stair will end, and measure down to the pad or the ground there. The run depends on the rise and the rise on where the run ends, so on sloping ground measure, calculate, move to the new landing spot, and measure again. If the stair will land on a concrete pad, measure to the top of the pad, not to the dirt it sits on.

Worked example: a deck 44 1/2 in. above a pad

This is the example the calculator opens with: 2x12 stringers, 2x treads 1 1/2 in. thick, 3/4 in. riser boards, a 10 1/2 in. run with a 3/4 in. nosing, and the deck as the top step.

• Risers: 44 1/2 ÷ 7 1/2 = 5.93, rounded up to 6. Each riser is 44 1/2 ÷ 6 = 7.417 in., which you lay out as 7 7/16 in.
• Treads: one fewer than risers, because the deck is the top step: 5 tread cuts of 10 1/2 in., so the stair runs 52 1/2 in. (4 ft 4 1/2 in.) out from the deck.
• Bottom cut: 7 7/16 − 1 1/2 = 5 15/16 in., so the first step is a full riser once the tread is on.
• Throat: each notch is 6 1/16 in. deep measured square to the edge, leaving 5 3/16 in. of the 11 1/4 in. board.
• Stringer: 63 7/16 in. long once cut. With the first notch point 3 7/16 in. from the foot end of the board, the last layout mark falls 67 11/16 in. from that end, so 8 ft 2x12s do it, three of them for a 36 in. wide stair.

Laying out a stringer with a framing square

1. Pick straight boards and find the crown. Sight down each 2x12 and lay it out with the crown (the high side of any bow) on the top edge, so the notches go on the crowned edge and the load straightens it.
2. Set the stair gauges: the riser height on the tongue (the short, narrow arm) and the run on the blade, on the same edge of the square. In the example that is 7 7/16 on the tongue and 10 1/2 on the blade.
3. Mark the notches. Start at the foot with both gauges against the top edge and the first notch point far enough from the end of the board that the toe of the stringer stays on it (3 7/16 in. in the example; the calculator gives the distance for your stair), and trace along the outside of the blade and the tongue. Slide the square toward the head until the blade's gauge sits on the mark the tongue just made, and repeat. On a long stringer, mark each notch point from the first with a tape instead (the calculator lists the distances), because a gauge setting rounded to 1/16 in. drifts on every step: 16 risers of 7.21875 in. stepped at 7 1/4 in. end up 1/2 in. out at the top, more than the 3/8 in. the code allows between risers.
4. Draw the bottom. From the first notch point, draw the bottom riser cut down the board parallel to the other riser lines, measure 5 15/16 in. along it (a full riser less the tread thickness), and draw the level floor cut square to it, parallel to the tread lines.
5. Draw the top. With the deck or floor as the top step, the last tread line ends at the head cut, a plumb line parallel to the risers that bears against the rim or header. With a flush top, the stringer has one more tread cut level with the top of the rim.

Printable full-size stringer template

The PDF draws the stringer flat on its board at exactly full size, tiled across Letter or A4 pages. The board's top edge runs along row A, so the notches usually fit on that one row of pages, and pages that would hold no cut line are left out. Each page carries its label (A1, A2 and so on), the pages it joins, a 1 in. or 25 mm check bar and crosshairs in the strips it shares with its neighbors. Trim the left and top margins, line up the crosshairs, tape, and lay the template on the board with its top edge on the board's edge. The first page is a summary with every number, the code check, the cut list, a map of the pages and two rulers to confirm the scale.

Cutting and test-fitting

Cut the long lines with a circular saw and stop at each inside corner, then finish the corner with a handsaw or jigsaw held plumb. Running the circular saw past the line into the corner cuts into the throat, which is the thinnest wood the stringer has. Cut one stringer first and test it in place: a level on each tread cut should read level, the head cut should sit tight against the rim at the right height, and the foot should bear flat. Fix the pattern if anything is off, then trace it onto the other boards. On treated lumber, treat the cut ends as the lumber's end tag instructs.

Common mistakes

• Forgetting the tread thickness. Cut the bottom with a full riser and every tread sits 1 1/2 in. too high: in the example the first step becomes 8 15/16 in. and the last 5 15/16 in., a difference the code limits to 3/8 in.
• Ignoring flooring still to come. Tile or hardwood laid after the stair changes the first or last riser by its thickness. Measuring from subfloor to subfloor, add the flooring to come at the top, subtract the flooring to come at the bottom, and choose a subfloor at the bottom when it goes in around the foot.
• Measuring the rise at the deck on sloping ground. The rise that matters is at the landing spot, which can be several inches lower than under the deck.
• Overcutting the inside corners, which saws into the throat.
• Notching 2x10s for a deck stair. The throat ends up a little over 3 in.; see the table below.
• Setting deck stringers on a patio slab. DCA 6 bears them on posts and footings below the frost line, not on a pad that isn't founded that deep.

The code limits, and where they come from

The calculator checks the stair against the stair section (R311.7) of the 2021 International Residential Code, the model code most US states and towns adopt for houses; the 2024 edition moved the same limits to R318.7. Deck stairs follow the same rules. Local codes can change any of these numbers, and most stairs need a permit, so treat the check as planning, not approval.

For deck stairs, the American Wood Council's DCA 6 prescriptive deck guide adds rules for the stringers themselves: 2x12 minimum, at least 5 in. of throat, cut stringers no more than 18 in. apart with at least three under a stair, a cut stringer spanning no more than 6 ft level (or a post and footing to shorten it), an intermediate landing on stairs over 12 ft tall, and footings under the bottom.

2x10 or 2x12 stringers, and how many steps one can span

The notch depth depends on the riser and run, not on the board, so it eats the same wood out of either size. A 2x10 is 9 1/4 in. deep and a 2x12 is 11 1/4 in.

Only the 2x12 clears DCA 6's 5 in. minimum. Length is the other limit: a cut stringer may span 6 ft measured level from the bottom riser to the head cut, which caps the number of tread cuts.

Past that, DCA 6 supports the stringers on a 4x4 post and footing partway down, or splits the stair with a landing.

Stringers with a landing

A landing is one of the step heights, so its finished surface has to be a whole number of risers above the lower floor or the steps on either side won't match. For a 105 in. rise with 14 risers of 7 1/2 in. and the landing after riser 7, the landing's finished surface is 52 1/2 in. up; decked with 1 1/2 in. treads, its framing tops out at 51 in. The lower stringer treats the landing as its top step, and the upper stringer sits on the landing and drops by the tread thickness like any other. Make the landing at least as wide as the stair and 36 in. deep in the direction of travel. Tick "Split into two flights" in the calculator to get both stringers, both templates and both cut lists.