Storage Tank Stairs Design

Number of steps = height of tank wall ÷ height of individual step.

Then it depends on what the local codes require or permit as good stair practice.

What does the 60° refer to? The slope of the stairs (an undesirable choice), or how far they can wrap around the tank? The height is 250 what?

250 height is height of individual steps.my tank is circular and i want for circular stairs.these stairs completes in 60 deg of tank.

That really cleared everything up nicely.

Divide the circumference of the tank by 6 to yield the horizontal distance or run you will have available in 60 degrees of tank circumference. as #1 said divide the height by 250 to get the number of steps. divide the run by number of steps to find tread width. use the same units for measurements.

If the vertical step-to-step rise is 250mm, the horizontal step-to-step tread should be about 190mm. (There are various guideline formulas, but I don't know if any of them are strictly mandated.) You still haven't said how tall the tamk is.