Free Stair Stringer Calculator
Calculate the exact rise, run, and stringer length for any staircase.
What is a stair stringer calculator?
A stair stringer calculator is a free online tool that helps you calculate stair stringer dimensions including rise, run, and number of steps for code-compliant stairs. It runs entirely in your browser — no signup, no app, and no data is ever sent to a server.
A stair stringer calculator gives you the exact dimensions for cutting stair stringers — the notched boards that support your staircase steps. Enter the total rise (vertical height from ground to landing) and the calculator tells you how many steps you need, the exact riser height per step, the total run, the stringer length, and the stair angle. Building codes in most areas require a maximum riser height of 7.75 inches and a minimum tread depth of 10 inches, so the calculator defaults to those standards but lets you adjust them.
How it works
The calculator divides the total rise by your maximum desired riser height to determine the number of steps. It then divides the total rise evenly across that many steps to get the exact riser height. The total run is the tread depth multiplied by (steps minus 1) — one fewer run than rise because the top step is the landing. The stringer length uses the Pythagorean theorem: √(total rise² + total run²). The angle is the arctangent of rise over run.
When to use a stair stringer calculator
Contractors building decks, porches, or interior stairs need accurate stringer dimensions before cutting. DIY homeowners building their own steps need to know exactly how to mark their stringers. The calculator is also useful for accessibility ramp design — a ramp is essentially a very shallow stair with a tiny rise per step.
Common mistakes when building stairs
The single biggest mistake I see in DIY stair building is inconsistent riser heights. Building codes across the US (IRC) and UK allow a maximum variation of 3/16 inch (about 4.8 mm) between the tallest and shortest riser in a single flight. The human brain detects tiny inconsistencies in step height — that's why tripping on stairs is so common in poorly built ones. Always divide the total rise evenly across all steps, which is exactly what the calculator does. Another mistake: forgetting to subtract tread thickness from the first riser cut. If you're using 1.5-inch tread boards, the bottom riser cut needs to be shorter by that amount or the first step will be too tall. The third issue is building stairs that meet code minimums without considering who will use them. A 7.75-inch riser with a 10-inch tread is technically legal, but it's steep and uncomfortable — especially for elderly users or kids. The ideal ratio is 7-inch rise and 11-inch run, which falls within the comfort zone of the standard rise-run formula (rise + run = 17-18 inches).
How to use this calculator
- Enter total rise — Measure the vertical height from the ground to the top of the landing in inches.
- Set tread depth — Enter your desired tread depth (typically 10-11 inches per building code).
- View stringer specs — The calculator shows number of steps, exact rise per step, stringer length, and angle.
Frequently asked questions
How do I calculate stair stringer length?
Use the Pythagorean theorem: stringer length = √(total rise² + total run²). The total rise is the vertical height from the ground to the landing. The total run is the number of treads × each tread's depth. A standard 10-foot rise with 7-inch risers and 10-inch treads needs a stringer about 14 feet long.
What is the standard stair rise and run?
The standard stair rise is 7 inches (maximum 7.75 inches per most building codes). The standard tread depth (run) is 11 inches (minimum 10 inches per IRC). The ideal ratio is a rise of 7 inches and a run of 11 inches, which gives a comfortable step angle of about 32 degrees.
How many stairs do I need for a 10-foot rise?
A 10-foot (120-inch) total rise divided by a 7-inch riser gives 17.1 steps — round to 17 steps. The actual riser height would be 120 ÷ 17 = 7.06 inches per step. The calculator automatically adjusts the riser height to divide evenly into the total rise.
What is the formula for cutting stair stringers?
Mark the top plumb cut, then measure down the stringer by the riser height, then out by the tread depth, repeating for each step. The bottom cut is parallel to the floor. Most contractors use a framing square with stair gauges. The calculator gives you the exact dimensions for every cut.
What is the maximum number of steps before a landing is required?
Most building codes (IRC R311.7.3) require a landing after every 12 feet (3.7 m) of vertical rise, which works out to roughly 20-21 steps at 7-inch risers. Landings must be at least as wide as the staircase and 36 inches (914 mm) in depth. This calculator helps you plan where landings are needed based on your total rise.
How thick should stair stringers be?
Minimum stringer thickness is 2x12 lumber (1.5 inches by 11.25 inches actual) for most residential codes. Never use 2x10 lumber for stringers — the notches reduce the structural capacity too much. The stringer length from the calculator accounts for the full board length you need to buy, so you can take the measurement directly to the lumber yard.