The spiral staircase calculator works out inner stringer length, actual riser rise and outer stair angle from angle of rotation, inside diameter, maximum riser rise, outside diameter, total rise, atan, one way, tan and headroom clearance. Enter what you have and the relationship is applied straight away, so you get the answer without working through the algebra yourself.
What Is the Spiral Staircase Calculator?
The spiral staircase calculator turns angle of rotation, inside diameter, maximum riser rise, outside diameter, total rise, atan, one way, tan and headroom clearance into inner stringer length, actual riser rise and outer stair angle, so you can order the right amount of material the first time.
Material estimates are where projects go over budget. Getting the quantities right before the delivery arrives is worth more than any discount on the order.
How to Measure for the Spiral Staircase
Measure everything in the same unit and take the largest dimension you can reasonably use rather than the average. Formwork, ground conditions and cutting waste all push the real figure above the theoretical one.
Where a plan calls for a specific thickness, check it against local building regulations before you order. The calculator reflects the relationship, not the code.
Allowing for Waste and Errors
Order a little more than the calculation suggests. The gap between the theoretical quantity and what actually arrives on site is normally waste, spillage, over-excavation and uneven grading, and all of it comes out of the same budget.
Write the figures down and compare them with what you actually used on site. That is how you build an estimate you can trust for the next job.
A Worked Example
Working through an example, with angle of rotation set to 10, inside diameter set to 5, maximum riser rise set to 2, the calculator returns number of steps of 5, and number of treads of 4, and actual riser rise of 2. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out inner stringer length?
Enter angle of rotation, inside diameter, maximum riser rise, outside diameter, total rise, atan, one way, tan and headroom clearance. The calculator then works through the relationship and reports inner stringer length, actual riser rise and outer stair angle.
What does the spiral staircase actually calculate?
It takes angle of rotation, inside diameter, maximum riser rise, outside diameter, total rise, atan, one way, tan and headroom clearance and converts them into inner stringer length, actual riser rise and outer stair angle using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter angle of rotation?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Is the answer exact?
It is as exact as the formula and the inputs allow. The method itself is the standard one for this problem, so the only sources of error are the figures you enter and the precision you ask for.
Do I have to fill in every field?
Only the fields a particular result depends on. If you leave one blank, the results that need it simply show a note instead of a number, and everything else still works.