Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Calculate riser count, riser height, total run, and stair angle from your total rise and chosen tread depth.
A staircase's total rise (floor to floor height) rarely divides evenly into a comfortable riser height, so building code and comfort standards work the other way: pick a target riser height (commonly around 7 to 7.75 inches), find the whole number of risers closest to that target, then divide the total rise evenly across them. This calculator does exactly that math, along with the resulting total run and stair angle.
Enter your total rise (the vertical floor-to-floor height in inches), your chosen tread depth (10 inches is a common comfortable default), and your target riser height (7.5 inches is a widely used starting point, though local code maximums vary and should always be checked).
Risers = round(Total Rise ÷ Target Riser Height)
Actual Riser Height = Total Rise ÷ Risers
Total Run = Tread Depth × (Risers − 1)
Angle = arctan(Riser Height ÷ Tread Depth)
Total run uses one fewer tread than riser, since the top riser lands on the upper floor itself rather than needing its own tread.
Building codes set maximum riser height and minimum tread depth limits that vary by jurisdiction (commonly around 7.75in max riser and 10in min tread for residential stairs in the US model codes) -- always verify against your local code before finalizing a stair design.
Once you have your riser height and tread depth, the Stair Stringer Calculator converts your total rise and run into the actual stringer board length to buy.
Suppose your measured floor-to-floor height is 96 inches, you plan on 10-inch treads, and you keep the 7.5-inch target riser. Dividing 96 by 7.5 gives 12.8, which rounds to 13 risers. The actual riser height is then 96 divided by 13, about 7.38 inches, and the total run is 10 times 12 treads, or 120 inches (10 feet). The resulting angle is roughly 36.4 degrees. Notice that the riser came out slightly shorter than your target because 12.8 was rounded up to 13. That is normal and usually desirable, since it keeps you under a maximum riser limit.
The most common source of stair errors is a bad rise measurement, not the arithmetic. A few habits help:
People adapt quickly to a consistent stair rhythm, and an uneven riser is a classic trip hazard. The calculator divides the rise evenly for exactly this reason. If you later cut stringers, keep in mind that the bottom riser is usually trimmed slightly by the thickness of the tread so that every step ends up the same height once treads are installed. Ask your inspector or local code office how they measure uniformity tolerances.
The angle is a quick comfort check. A stair in the mid-30-degree range feels like a typical residential staircase. Angles that climb noticeably higher feel steep and need more careful attention to tread depth and handrails, while very shallow angles consume a large amount of floor space. If the total run does not fit your available space, you can experiment with a shorter tread or a slightly taller riser, but only within the limits your local code allows.
Because the total rise must be divided evenly across a whole number of risers -- the calculator finds the closest whole riser count to your target, then recalculates the exact height that results.
Most residential stairs use risers between about 7 and 7.75 inches -- lower risers feel gentler but require more total run (floor space) for the same total rise.
No -- measure your total rise from finished floor to finished floor, and add any tread nosing overhang separately if your stringer layout needs it.
Re-check the total rise entry. A unit mix-up, such as entering feet instead of inches, produces an absurd riser count. The rise should be entered in inches.
Only by adding a riser. Lower your target riser height slightly so the rounding lands on one more step; the total run will grow by one tread depth as a result.
No. It models one straight flight. If a landing is required, treat each flight as its own rise and run and check landing size requirements with your local code office.