A staircase can reach the required height and still fail to fit the available space. The Whatson Staircase Calculator shows total rise, adjusted riser height, tread count and horizontal run together so you can see that relationship.
It is a straight flight geometry and quantity worksheet. Its results do not certify building code compliance or design the reinforcement.
Start with the finished level difference
Total rise is the vertical difference between the relevant finished levels. Enter it in the selected measurement unit. Stair width follows that unit too.
Target riser, tread depth and optional waist thickness are entered in inches. The target riser is used to choose a whole number of risers. The actual riser is then recalculated so all risers share the total rise evenly.
Using rough structural levels while forgetting the finished floor build ups can give a different rise from the completed staircase. Confirm the level basis with the drawing.
Eighteen risers are not eighteen lower treads
For a 10 ft rise, target riser 7 inches and tread 10 inches, the checked result is 18 risers. Each actual riser is about 6.667 inches.
The upper floor is treated as the final arrival surface, so the flight has 17 treads below it. At 10 inches each, the horizontal run is about 14.17 ft. The geometric flight angle is about 35.22 degrees.
That run needs to be compared with the intended plan space. It does not include a landing or a turn.
The concrete result has a narrow scope
With a 3.5 ft stair width, 6 inch waist and 5% allowance, the same checked example estimates about 1.31 m³ of concrete.
The model combines a sloping waist slab with triangular tread wedges. It excludes landings, supports, beams, finishes and reinforcement. Actual detailing can therefore require a different takeoff. A zero waist setting omits the concrete quantity from the displayed estimate.
Changing the target riser can cause a jump
The riser count is rounded up, so a small input change can add a whole riser and alter the tread count. Review the whole result after any change; do not keep an earlier run while using a new riser height.
Headroom, guards, handrails, tread rules and local approval requirements need a design review outside this tool. Use the calculator to check dimensions against an approved arrangement, then price concrete in PKR per m³ if required.