This calculator allows you to quickly estimate max allowable pressure for a cylinder tube or a pipe (when you know what material it is made of). It uses two generally accepted formulae - the Barlow's and the Lame's.
For your reference: the ST52.3, the most common steel grade for cold-drawn cylinder tubes, has a typical yield of ≥350 MPa, and a typical strength of about 490-630 MPa. Make sure that you know what kind of alloy your pipe or tube is made of, and don't forget that a "conservative" safety factor is never a bad thing (especially if your application is dynamic!).
Note: You can switch between units to quickly transform one into the other. Some "polite rounding" occurs as you do that.