Free stair calculator. Enter total rise in inches to find how many steps you need and the riser height for even, comfortable stairs.
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Divide total rise by a 7.5 inch target riser and round up to whole steps, then divide total rise by that step count for the exact riser height. Every riser in a flight must be the same height, or the stairs will trip people.
To calculate stair steps, divide total rise by a target riser height and round up to whole steps. A total rise of 108 inches needs 15 steps at 7.2 inches each, since 108 divided by 7.5 is 14.4, rounded up to 15. A rise of 96 inches needs 13 steps at 7.38 inches each.
The riser is the vertical face of each step, the tread is the flat surface you step on, and the nosing is the tread edge that overhangs the riser below. Total rise is floor to floor height, total run is the horizontal length of the whole stair, and the stringer is the sloping board that supports treads and risers.
With this calculator 7.5 inch target riser, the results are: 96 inches gives 13 steps at 7.38 inches, 102 inches gives 14 steps at 7.29 inches, 108 inches gives 15 steps at 7.20 inches, 114 inches gives 16 steps at 7.13 inches, and 120 inches gives 16 steps at 7.50 inches. Other calculators using a 7 inch target give 17 steps for 120 inches, which is why step counts differ between tools: the target riser matters.
Treads are usually one fewer than risers, since the top floor acts as the last tread. With 10 inch treads, a 108 inch rise with 15 risers gives 14 treads and a total run of 140 inches. Stringer length is the diagonal: square root of (108 squared plus 140 squared) = about 176.8 inches, before end cuts. Stair angle is arctan(riser / tread), which is arctan(7.2 / 10) = about 35.8 degrees.
Building code requirements under the US International Residential Code for homes say risers may not exceed 7.75 inches, treads must be at least 10 inches deep with a nosing or 11 inches without one, headroom must be at least 6 feet 8 inches, and minimum width is 36 inches. Riser and tread variation within a flight must stay within 3/8 inch. In England, private stairs under Approved Document K allow risers up to 220 mm with a minimum going of 220 mm and maximum pitch of 42 degrees. Always confirm local amendments before building.
A long-standing comfort rule, often credited to Blondel, says 2 times riser plus tread should be about 24 to 25 inches, or 60 to 65 centimetres. A 7.2 inch riser with a 10 inch tread gives 24.4 inches, right in range. Higher risers call for shallower treads and vice versa, and values well outside the range feel awkward even when they meet code.
Deck stairs follow the same geometry, with total rise measured from deck surface down to the finished ground where the bottom step lands. Use rot-resistant or treated lumber, rest stringers on a solid base such as a concrete pad, leave small gaps between tread boards for drainage, and choose slip-resistant surfaces. On sloping ground, measure at the point where the bottom step will actually land.
Measuring to the subfloor instead of the finished floor leaves the first or last step a different height. Counting treads the same as risers forgets the top floor as the last tread. Mixing inches and centimetres, ignoring headroom under beams, and letting riser heights vary are all common errors. Even a small riser difference breaks walking rhythm and causes trips, which is why codes limit variation.
Most comfortable stairs use risers between 7 and 7.75 inches, with treads about 10 to 11 inches deep. Shorter risers feel easier but need more steps and more run.
People learn the step height within a few steps and stop looking at their feet. One riser that differs by even a small amount is a common trip hazard.
A 108 inch floor-to-floor rise usually needs 15 steps at 7.2 inches with this calculator 7.5 inch target. With a 7 inch target the same rise gives 16 steps, so always note which target a calculator uses.
Most single-floor rises of 8 to 9 feet work out to 14 to 16 steps, depending on target riser. Divide total rise in inches by 7 and round up for a quick estimate, then use the calculator for the exact riser height.
The riser is the vertical height of each step, and the tread is the horizontal part you step on. One tread per riser, except the top landing, which counts as the last step, so treads are risers minus 1.
Divide the total rise in inches by the number of risers you want. For a 108 inch rise split into 15 steps, each riser is 108 / 15 = 7.2 inches.
Under the US IRC a single flight may not rise more than 12 feet 7 inches (151 inches) without a landing, and landings are also needed at top and bottom and where a door opens onto the stair. Landings also break up long runs for safety. Check local code.
A stringer is the sloping board that supports treads and risers. Its straight-line length is the square root of (total rise squared plus total run squared). Buy a longer board to allow for end cuts and top bearing.
Under the US IRC, residential risers may not exceed 7.75 inches and treads must be at least 10 inches with a nosing, or 11 inches without one. Local amendments may differ, so confirm with your building department.
Measure from the top of the finished floor at the bottom to the top of the finished floor at the top, including flooring thickness at both ends. If flooring is still to be laid, add its thickness, or the first and last steps will differ.
Yes, the geometry is the same. Measure total rise from deck surface to the finished ground where the bottom step lands, and follow local code for decks, including guards and handrails.