How to Cut Stair Stringers

The stringer is the notched board that the treads and risers sit on - the backbone of the staircase. Cutting one accurately is mostly careful marking with a framing square.

Before you start: get your numbers

You need your riser height and tread depth (the going), worked out from the total rise - see stair rise and run explained. The stair calculator gives you these and draws the profile, so you can mark the stringer with confidence.

Step 1: Set up the framing square

On a straight, knot-free board (usually a 2×12):

1. Clamp stair gauges (the little brass buttons) to the framing square - one at your riser height on the tongue (short arm), one at your tread depth on the blade (long arm).
2. Slide the square along the top edge of the board so both gauges touch the edge. That single position marks one step - the riser up the tongue, the tread along the blade.

Step 2: Step off the flight

Mark around the square, then move it along so the next step starts where the last tread mark ended. Repeat for the full number of steps. Keep each placement tight to the edge - small drifts add up over a flight.

Step 3: Mark the top and bottom cuts

• Top: a vertical plumb cut where the stringer meets the upper floor or header.
• Bottom: a horizontal seat cut where it lands on the base.

Step 4: The all-important deduction

Trim the bottom of the stringer by one tread thickness. This “dropping the stringer” keeps the first step level with the rest once the treads are fitted. Forget it and your bottom step is one tread-thickness too tall - the classic stringer error and a trip hazard.

Step 5: Cut

Cut the notches with a circular saw, stopping on the line, and finish the inside corners with a handsaw or jigsaw so you do not overcut and weaken the board. Use the first stringer as a template for the rest.

How many stringers

Space them no more than ~16 in (400 mm) apart. A standard ~36 in (900 mm) stair needs three (two outers, one centre); wider stairs need more so treads do not flex.

Next

Building exterior steps off a deck? The same stringer method applies, plus footings and ledger fixing - see how to build deck stairs, and check your geometry first with the stair calculator.