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Cut a stringer from a 2×12

Framing-square settings, both cut angles, the throat check, the drop, and how many boards to buy — step by step.

Units

Laying it out with a framing square

A stringer is marked out by walking a framing square down the board, once per step. The rise goes on the tongue (the narrow arm) and the going on the blade (the wide one). Stair gauges — the little brass clamps — hold both settings so that every notch is a copy of the first rather than a fresh measurement with a fresh chance to be wrong.

Set stair gauges at the rise on the tongue and the going on the blade, then step the square along the board. The gauges are what make every notch identical.riseon the tonguegoingon the bladethe board — crowned edge uppermoststair gauges — clamp them on once,then every notch is a copy of the firststep it along, and again
Set stair gauges at the rise on the tongue and the going on the blade, then step the square along the board. The gauges are what make every notch identical.

The two angles

Each notch is one plumb cut and one level cut, and they always add to 90°. The plumb cut is the one that ends up vertical in the finished stair; the level cut is the tread seat.

Plumb and level cuts are complementary. The level cut is too steep for most mitre saws, which is why stringers are marked out and cut with a circular saw.square across the board34°PLUMB cutvertical once installed56°LEVEL cuthorizontal once installedThe two angles always add to 90°.The level cut is the steeper of the two, past what mostmitre saws will swing — and a 2×12 is wider than mostwill cross-cut anyway. Stringers are a circular-saw job.
Plumb and level cuts are complementary. The level cut is too steep for most mitre saws, which is why stringers are marked out and cut with a circular saw.

The throat is what decides the board

Cutting the sawtooth removes a triangle from each step. What is left behind the notches is the entire structure of the stringer, and it is narrower than people expect — a comfortable 7″ by 10½″ step takes almost six inches out of an 11¼″ board.

The throat is the narrowest remaining material behind the notches. It is the reason stringers are cut from 2×12 and not 2×10.cut awayTHROATall that carries the loadcutdepthWhat is left behind the notches is the whole structure.5″ is what most inspectors look for; below about 3½″ the board is spent.Deep risers and deep treads both eat into it.
The throat is the narrowest remaining material behind the notches. It is the reason stringers are cut from 2×12 and not 2×10.

Five inches of throat is what most inspectors look for, and about 3½″ is where the board is generally considered spent. Neither figure is a flat rule in the IRC, so treat them as common practice to confirm with your building department rather than as a citation. If the throat comes up short the answers are a deeper board — LVL at 11⅞″ buys a little — or an uncut housed stringer, where the treads sit in routed trenches and the board is never notched at all.

The drop at the bottom

The single commonest stringer mistake, and it is made before the stringer ever leaves the bench.

The drop: trim the bottom of the stringer by one tread thickness, or the first step finishes taller than the rest.as laid outafter the dropfloor8″floor7″Cut the bottom of the stringer down by one tread thickness before you stand it up. The treadboard adds that height back on every step except the first, where the floor is already there.
The drop: trim the bottom of the stringer by one tread thickness, or the first step finishes taller than the rest.

Cutting it

Stop the circular saw short of every inside corner and finish with a handsaw. An overcut kerf is a crack started in the part that carries the load.WRONGkerf runs on intothe throatRIGHTstop short, finish thecorner with a handsawA circular blade is round, so by the time it has cut through at the corner it has already cutfurther on the underside. Every one of those overruns is a crack started in the throat.
Stop the circular saw short of every inside corner and finish with a handsaw. An overcut kerf is a crack started in the part that carries the load.

Cut the first stringer, then use it as the template for the rest rather than marking each one out again. Three boards marked independently will differ; three traced from one will not.