How to Cut Stair Stringers
Before marking anything
Get the numbers from the stair calculator: number of risers, exact riser height, tread depth and minimum stringer length. Then buy a board longer than that — the calculated length is the straight line through the notches, with nothing spare for the cuts or the top connection. For a 14 ft calculated length, buy 16 ft.
Choose the straightest stock you can find, usually 2x12. A crowned or twisted stringer transfers its bow into every tread.
Laying out with a framing square
- Set stair gauges — the small brass clamps — on the framing square at your rise on the tongue and your run on the blade. Now every step is marked identically without re-measuring.
- Start at one end and mark the first triangle. Slide the square along so the run mark meets the previous rise mark, and repeat for every riser.
- Count as you go. Mark the number of risers the calculator gave you, not one more or one fewer. Miscounting is the most common error here and it is invisible until the stair is installed.
- Mark the bottom and top cuts. The bottom cut is horizontal where the stringer meets the floor; the top is vertical where it meets the header or hanger.
Dropping the stringer — the step everyone forgets
Once the notches are cut, the top surface of every notch is where a tread will sit. The tread has thickness. Install the stringer as cut and the bottom riser ends up taller than all the others by one tread thickness, while the top riser ends up shorter by the same amount — breaking the 3/8 in uniformity rule immediately.
The fix, called dropping the stringer: cut the bottom horizontal cut down by the thickness of one tread. With 1 in treads, remove 1 in from the bottom.
One caveat that changes the number: if finished flooring is going down at the bottom but not the top, or the other way round, the drop must account for that difference too. Measure to finished surfaces on both levels and adjust.
Cutting
- Circular saw to the lines, stopping just short of the inside corner. Do not overcut into the corner — a kerf past the corner is a stress point that can split the stringer.
- Finish the corners with a handsaw or jigsaw.
- Cut the first stringer, then use it as a template for the rest. Marking each one separately introduces small differences that show up as uneven treads.
- Test-fit the first stringer before cutting the others: bottom sitting flat, top meeting the header, and a level laid across the notches reading level.
How many stringers
Three for a 36 in wide stair, roughly at 16 in centres. Wider stairs need more, and treads thinner than 5/4 stock or stairs carrying heavy loads need closer spacing. Check span requirements in your code — cutting notches removes a great deal of a 2x12's depth, and a notched stringer is much weaker than the board it came from.
Enter the total rise — floor to floor, not floor to ceiling — and get the riser count, the exact riser height, the total run, the stringer length and the angle, checked against the usual residential limits.
Frequently asked questions
What does dropping the stringer mean?
Cutting the bottom horizontal cut down by the thickness of one tread. The notches you cut are where treads sit, so without the drop the bottom riser would be one tread thickness taller than every other riser, and the top one shorter.
How do I lay out stair stringers with a framing square?
Clamp stair gauges to the square at your riser height on the tongue and your tread depth on the blade, mark the first triangle, then slide the square so the run mark meets the previous rise mark and repeat for each riser. Every step comes out identical.
How many stringers do I need?
Three for a typical 36 inch wide stair at about 16 inch centres, and more for wider stairs, thinner treads or heavier loads. A notched 2x12 is far weaker than the board it was cut from, so check span requirements.
What length board do I need for a stringer?
Longer than the calculated diagonal. The stair calculator gives the straight-line length through the notches — for example 14 feet 1 inch for a 9 foot rise — so buy a 16 foot board to leave material for the cuts and the top connection.