Stair Calculator

Measure the total rise from finished floor to finished floor, then divide by your target riser height, about 7 inches, and round to a whole number. A 108 inch rise gives 108 / 7 = 15.4, so 15 risers of 7.2 inches. You get one fewer tread than risers because the upper floor is the last tread.

Rise is the total vertical height between floors. Run is the horizontal distance the stairs cover. Divide the rise by a target riser to find the number of risers, subtract one for the treads, and multiply the treads by the tread depth. For 15 risers and a 10 inch tread the run is 14 × 10 = 140 inches.

It depends on the riser you choose. Three risers give 8 inches each, which is steep. Four risers give 6 inches each, which is gentler but needs three treads. At a 7 inch target the calculator rounds 24 / 7 = 3.4 to 3, so try a lower target if you prefer four.

Total rise is the vertical distance from the finished surface of the lower floor to the finished surface of the upper floor. Include any flooring that will be laid. It is the single most important measurement, because every riser height and the whole layout come from it.

Total run is the horizontal length the stairs take up, measured along the floor. For a straight flight it equals the number of treads times the tread depth. If the stairs include a landing, add the landing's depth to get the total space needed.

Riser height equals total rise divided by the number of risers. The number of risers comes from dividing the total rise by a target height and rounding to a whole number. Using the exact result keeps every riser identical, which matters because uneven risers are a common cause of trips.

The top step is the upper floor itself, so the last riser ends on the floor rather than on a tread. A flight with 15 risers has 14 treads. Counting a tread for every riser adds a step that does not exist and makes the run one tread too long.

Treat the rise and the run as the two legs of a right triangle and find the diagonal: stringer length = square root of (rise squared plus run squared). For a 108 inch rise and a 140 inch run that is 176.8 inches. Cut the board longer than this to allow for the top and bottom cuts.

With 5 risers of 7.5 inches and 4 treads of 10 inches, the rise is 37.5 inches and the run is 40 inches, so the stringer diagonal is about 54.8 inches, or 4.6 feet. Buy a board a little longer to allow for the cuts at each end.

With 2 risers of 7.5 inches and one 10 inch tread, the rise is 15 inches and the run is 10 inches, so the diagonal is about 18 inches. Short flights still follow the same triangle: stringer length is the square root of rise squared plus run squared.

With 7 risers of 7.5 inches and 6 treads of 10 inches, the rise is 52.5 inches and the run is 60 inches, so the stringer diagonal is about 79.7 inches, or 6.6 feet. Add some extra board length for the top and bottom cuts and the seat of the stringer.

A common layout has one stringer along each side and one in the centre, with more added for wider stairs. The right number depends on the stair width, the tread material and your local code, so treat three as a starting point and check what your building department requires.

The 7-11 rule is shorthand for a riser of about 7 inches and a tread of about 11 inches, a comfortable step. It is a rule of thumb, not a legal limit. Local building codes set the actual allowed ranges, so use the figure as a design target and confirm the limits where you live.

Several rules of thumb circulate under names like the 27 rule or the 7-11 rule, and they are not code. The one with a documented source is Blondel's: 2 x riser + tread equals the step length. The calculator shows that number for your layout. For legal limits, use your local building code.

Nicolas-François Blondel, in work published between 1675 and 1683, was the first known person to link tread and riser sizes, stating that 2 x riser + tread gives the step length. Taller risers call for shallower treads and the formula keeps the stride comfortable. The calculator reports this value for your stairs.

Many people find risers of about 7 inches (18 cm) comfortable, with treads of 10 to 11 inches. Steeper risers shorten the run but are harder to climb. Your local code sets a maximum riser height, and the calculator lets you pick any target and see the angle and step length.

An 8 inch riser is steeper than the common 7 inch target and gives a steeper angle, but whether it is allowed depends on your code and the building type. OSHA's workplace limit is 9.5 inches. For a home, check your local building department before settling on 8 inches.

Ten to eleven inches is the usual choice for house stairs. The tread depth is measured from the back of one tread to the back of the next, so a nosing that overhangs does not shorten it. A deeper tread lowers the stair angle and increases the run.

Take the inverse tangent of riser divided by tread. A 7 inch riser with a 10 inch tread is atan(0.7) = 35 degrees, and 7 by 11 is 32.5 degrees. The calculator gives the angle for your exact riser height. OSHA's workplace stair range is 30 to 50 degrees.

Measure from the finished surface of the lower floor to the finished surface of the upper floor, in one straight vertical line at the stair opening. Include any flooring or carpet that will be installed. If the floors differ in thickness, use the final heights so that the first and last risers match the rest.

Choose the number of landings and their depth in the calculator. The landing's depth is added to the total run, because it is a flat section, but it does not change the stringer calculation for the sloped parts. OSHA's workplace rule asks for landings at least 30 inches deep.

Use the same method in centimetres. For a 270 cm rise, an 18 cm riser gives 15 risers, a 25 cm tread gives 14 treads and a run of 350 cm. Switch the unit setting to centimetres and the calculator does it all, including the stringer and angle.

Work out the steps as for a straight flight, then add the landing depth to the run for the footprint. A 9 foot rise with a 36 inch landing has 15 risers, 14 treads and a total run of 140 + 36 = 176 inches. Split the steps into two flights if the landing sits partway up.

A straight flight needs a run equal to the number of treads times the tread depth, plus any landing and the width of the stairs. A 9 foot rise needs about 140 inches (11.7 feet) of run at a 10 inch tread. Steeper stairs shorten the run, shallower stairs lengthen it.

For standard workplace stairs, OSHA 29 CFR 1910.25 calls for an angle between 30 and 50 degrees, a maximum riser height of 9.5 inches, a minimum tread depth of 9.5 inches, a minimum width of 22 inches between vertical barriers, and landings at least 30 inches deep. These cover industrial stairs, not home codes.

The calculator does the geometry, not code checking. Residential building codes set their own limits on riser height, tread depth, headroom and handrails, and they differ by place and by year. Take the riser, tread and run it gives you to your local building department and confirm them before building.

Yes, the geometry is the same. Measure the total rise from the ground surface (or the top of the landing pad) to the finished deck surface, choose your riser and tread, and read the number of steps and the stringer length. Check your local code for deck-specific rules such as the footing and guard requirements.

The calculator rounds the number of risers to a whole number and then recalculates the riser height so every step is identical. If the exact riser comes out higher or lower than you want, change the target riser and watch the rounding move between, for instance, 14 and 15 risers.

Divide the length in inches by 12. A 176.8 inch stringer is 14.7 feet, so you would plan on a board of at least that length plus trimming allowance. Lumber is sold in set lengths, so round up to the next length your supplier stocks and cut the stringer from it.

It does not. The riser height depends only on the total rise and the number of risers. Changing the tread depth changes the run, the stringer length and the angle. The riser changes only when the number of risers changes, which happens when you alter the rise or the target riser.

A nosing is the part of a tread that overhangs the riser below it. Because treads are measured from the back of one to the back of the next, the nosing does not add to the run. It does make the visible tread look deeper and gives the foot a little extra room.

Measure from the ground, or the top of the landing pad, up to the finished deck surface. That distance is the total rise. Divide it by a target riser near 7 inches, round to a whole number of risers and use the exact riser the calculator returns, so every step on the deck stairs is identical.

A flight can have as few as one riser, but the geometry works the same. A 7 inch rise needs 1 riser and no treads, while a 14 inch rise needs 2 risers and 1 tread. The calculator always returns at least one riser and treads equal to risers minus one.

Each notch is one riser high and one tread deep, so mark the riser height and tread depth alternately along the board using a framing square. The calculator gives the exact riser and tread values to mark and the diagonal length the board must cover, before you add allowance for the top and bottom cuts.