σ = pr/t where r is the inside radius and t is the wall thickness
σ = p(R2 + r2) / (R2 - r2) where r is the inside radius and R is the outside radius (r plus the wall thickness)
Generally, a cylinder is considered to be "thin-walled" if its radius r is larger than 5 times its wall thickness t (r > 5 · t).
These calculators do nothing beyond evaluating the stated equations using the data supplied by YOU. Use stress values calculated with these calculators at your own risk.