What is the standard riser height for residential stairs?

The standard riser height for residential stairs is 7" to 7-3/4", with 7-1/2" being the most common target. The IRC sets a maximum of 7-3/4" (R311.7.5.1, 2021 edition). Most framers aim for 7" to 7-1/2" because this range pairs well with a 10" to 11" tread depth for a comfortable walking angle.

How do you calculate the number of stairs needed?

Divide the total rise (floor-to-floor height in inches) by your desired riser height, then round to the nearest whole number. For example, a 109" total rise divided by 7.5" gives 14.53, which rounds to 15 risers. The number of treads is always one fewer than the number of risers, so this flight would have 14 treads.

What is the minimum tread depth for stairs?

The minimum tread depth is 10" for residential stairs under the IRC and 11" for commercial stairs under the IBC (2021 editions). Tread depth is measured horizontally from the front edge of the nosing to the front edge of the next nosing above. A deeper tread of 11" to 11-1/4" is more comfortable and preferred by most builders.

How long should a stair stringer be?

Stringer length equals the square root of (total rise squared plus total run squared). For a typical flight with 109" total rise and 140" total run, the stringer length is about 177-7/16" (approximately 14' 9-7/16"). Always add at least 12" to your lumber length for the top and bottom cuts and any fitting adjustments.

What is the 7-11 rule for stairs?

The 7-11 rule is a guideline stating that stairs are most comfortable with a 7" riser height and an 11" tread depth. This combination produces a walking angle of about 32 degrees. A related check is that the sum of one riser plus one tread should fall between 17" and 18" — the 7-11 combination sums to 18", right at the upper comfort limit.

How much headroom is required for stairs?

A minimum of 6' 8" (80 inches) of headroom is required by both the IRC and IBC (2021 editions). Headroom is measured vertically from the nosing line to the nearest overhead obstruction such as a header, floor joist, or ceiling. If ductwork or beams run across the stairwell, measure to the lowest point.

What size lumber do you need for stair stringers?

Most stair stringers require a 2x12 (actual depth 11-1/4"). After notching, the remaining throat depth must be at least 3-1/2" per code. A 2x12 accommodates risers up to about 7-3/4" with a standard tread run. For low-rise stairs with small notches, such as short deck stairs with a 6" rise, a 2x10 (actual 9-1/4") may be sufficient.

Free Stair Calculator — Rise, Run & Stringer Length

How to Use the Stair Calculator

How to Calculate Stair Rise and Run

To calculate stairs, divide the total rise (floor-to-floor height in inches) by your desired riser height to get the number of risers, then subtract one to get the number of treads. Multiply the number of treads by your tread depth to find the total run. This calculator handles all of these calculations instantly, including stringer length, code compliance, and headroom clearance.

Measuring Total Rise

Total rise is the vertical distance from the surface of the lower finished floor to the surface of the upper finished floor. This is the single most critical measurement in stair layout — every other dimension derives from it.

Measure from finished floor to finished floor, not from subfloor to subfloor. If the finished flooring has not been installed yet, add its thickness to your measurement. For example, if you measure 108" from subfloor to subfloor and both floors will receive 3/4" hardwood, your total rise is 108" + 3/4" (upper floor) − 3/4" (lower floor) = 108". If only the upper floor gets finish material, add only that thickness.

For a floor-to-floor height of 9' 1" (109 inches), dividing by a target riser height of 7-1/2" gives 14.53 — round up to 15 risers. The actual unit rise becomes 109" ÷ 15 = 7.267", or approximately 7-1/4". This keeps each riser comfortably within code limits.

The Rise-Run Relationship

The number of treads always equals the number of risers minus one. The top "tread" is the upper floor itself, so a flight with 15 risers has 14 treads. Multiply the tread count by the unit run (tread depth minus any nosing overhang) to calculate total run — the horizontal distance the stair covers.

The industry standard known as the 7-11 rule recommends a 7" rise paired with an 11" run. This combination produces a comfortable walking angle of roughly 32 degrees. Both the IRC and IBC reference this proportion, and most experienced framers use it as a starting target before adjusting to fit the available space.

A useful cross-check: the sum of one riser plus one tread should fall between 17" and 18". Values outside this range tend to feel either too steep or too shallow for normal foot traffic.

IRC vs IBC Code Requirements

Building codes set maximum and minimum dimensions to ensure safety. The two most widely adopted codes in the United States are the International Residential Code (IRC) for dwellings and the International Building Code (IBC) for commercial and public buildings.

IRC R311.7.5.1 (2021 edition) — Residential: Maximum riser height 7-3/4", minimum tread depth 10", minimum headroom 6'8", minimum stair width 36", maximum nosing projection 1-1/4", maximum riser variation 3/8" within a flight.
IBC 1011.5.2 (2021 edition) — Commercial: Maximum riser height 7", minimum tread depth 11", minimum headroom 6'8", minimum stair width 44" (or 36" for occupant loads under 50), maximum riser variation 3/8".

Important: Many states and municipalities amend these codes. Always check your local jurisdiction's adopted code edition and any local amendments before finalizing your stair design. This calculator flags violations against the standard IRC and IBC limits, but your local inspector has the final word.

Stringer Layout Basics

Stringers are the notched diagonal boards that support the treads and risers. Use a framing square with stair gauges clamped at the unit rise and unit run to mark each step along the stringer stock. The cut follows a sawtooth pattern, with each notch removing material from the board.

The stringer throat — the narrowest remaining width of the stringer after notching — must be at least 3-1/2". This typically means a 2×12 is required for risers above 7-1/2" or runs above 10". For smaller stairs (such as short deck stairs with a 6" rise and 10" run), a 2×10 may provide adequate throat depth, but always verify by drawing the layout to scale or using this calculator's stringer diagram.

Pro Tips

Measure total rise in three spots across the stair opening — left edge, center, and right edge — and use the longest measurement. Floors are rarely perfectly level, and using the longest dimension prevents a short riser at the top.
Check that both the upper and lower landing surfaces are level before measuring. A landing that slopes toward the stair opening will throw off your total rise and produce uneven risers.
Add 1/16" to your unit rise when marking stringers to prevent cumulative error. Over a 15-riser flight, pencil-line thickness and saw kerf can shave nearly 1/4" from the total rise. The extra 1/16" per step compensates.
Always check local code amendments before ordering materials — some jurisdictions modify the standard IRC or IBC riser and tread limits, and a few still enforce legacy codes with different requirements.
Cut one stringer first and test-fit it in place before cutting the rest. Clamp it to the upper floor frame and set a level on the tread notches. Adjust if needed — it is far cheaper to recut one board than to waste an entire set of stringer stock.