how to calculate the radius os a spiral?

Question

In a spiral staircase case the inner radius is very close to the external radius regardless the distance between them. If you look the staircase from above, like in a floorplan, you may have an inner radius of, let's say, 1 meter and an external radius of 2 meters but when you shape the railings for this hipotetycal staircase the inner railing will have a raidus very close to 2 meters. This is because they are both covering the same vertical distance. I know this by practice but would love to learn a mathematical formula to calculate that.

Answer 1

1. the werd is staers, not staerkase

2. yu better put raels around the sides

3. ???? yu hav a hole with radius=2 meters, & nael the steps tu the wall av hole ???

Me thank sumthun like this require speshalist hu dun it B4

normal for steps is rise =bout 7 inch & run bout 9inch

But serkel result in run vary...more neer outside wall, small neer senter.

normal staers...get vetikal hite in inches, sae 9ft up tu floor 2...9*12=108 inches

divide 108 bi 7 tu get 15.428571 steps

round up tu 16 steps, so eech step=108/16=6.75 inch or 6 & 3/4 inch

me spekt speshalist hav a vershun for serkel staers