Stair Stringer Calculator - Free Riser & Tread Layout Tool

Start with your total rise (floor to floor, in inches). Divide by your target riser height (7" to 7.5" is ideal) to get the number of risers. Round to the nearest whole number. The actual riser height is total rise divided by that number. Treads = risers minus 1. Total run = treads times tread depth. Stringer length = square root of (total rise squared + total run squared). For a 9-ft (108") rise with 11" treads, you get 15 risers, 14 treads, a total run of 154", and a stringer length of about 15.7 ft.

The International Residential Code (IRC) sets the maximum riser height at 7.75 inches (7-3/4"). Most inspectors enforce this strictly. The practical sweet spot is 7" to 7.5" per riser. Risers in a single stairway cannot vary by more than 3/8" from tallest to shortest, so accurate measurement and layout are critical. If your rise calculation gives you risers over 7.75", add one more riser to bring the height under the limit.

The rule of thumb is one stringer every 16-18 inches of stair width. For a 36" wide stair: 3 stringers (one on each side plus one center). For 48" width: 4 stringers. Most building codes require stringers no more than 18" apart for 5/4 deck boards and no more than 16" apart for 2x treads. If you are using composite treads, check the manufacturer specs - some need support every 12".

2x12 is the standard for stair stringers. After you cut the notches for treads and risers, the remaining "throat" of the stringer must be at least 3.5 inches deep (IRC requirement). A 2x12 gives you an 11.25" actual width, leaving enough throat after a 7.5" rise and 11" run cut. Never use 2x10 for notched stringers - the throat gets too thin and the stringer will crack under load.

The 7-11 rule is a comfort guideline: riser height + tread depth should equal 17 to 18 inches. A 7" riser with an 11" tread gives you 18" - right in the sweet spot. Stairs that fall outside this range feel either too steep (riser too tall, tread too shallow) or too shallow and sprawling (riser too short, tread too deep). The IRC minimum tread depth is 10", and the max riser is 7.75", so the code range naturally overlaps with this rule.

A basic exterior deck stair set (3 stringers, pressure-treated lumber, 4-6 steps) runs $200-$500 in materials. Interior stairs with hardwood treads and closed risers cost $800-$2,500+ in materials. Labor for cutting and installing a standard set of stringers runs $150-$500 depending on complexity. Total installed cost for a basic deck stair is typically $400-$1,000, while a full interior staircase can run $2,000-$5,000+.

Mark the stringer with a framing square using stair gauges set to your riser height and tread depth. Draw the first riser line, then walk the square down the board marking each step. Important: subtract one tread thickness from the bottom riser so the first step equals all the others once the treads are installed. Cut the notches with a circular saw, but stop short of the inside corner. Finish the cut with a handsaw or jigsaw to avoid over-cutting, which weakens the stringer. Always cut a test stringer first and check it in place before cutting the rest.

The IRC requires a minimum clear width of 36 inches for residential stairs, measured between the finished walls or guards. This does not include handrail projections - handrails can project up to 4.5" from each side. For a 36" clear width between handrails, the rough stair opening needs to be about 42-44". Exterior deck stairs typically follow the same 36" minimum unless local codes differ.

Yes. Drop the stringers by the thickness of one tread at the bottom. If you are using 5/4 deck boards (1" actual) or 2x treads (1.5" actual), cut that amount off the bottom of each stringer. Without this adjustment, the first riser will be taller than the rest by the tread thickness, which violates the 3/8" variance rule and will feel wrong underfoot. This is the most common stair-building mistake.