I built a Kiln, and I would check its quality. Is there any way to do that, or does I need to calculate it from the formulaes given on the Wiki, assuming I remember the overall clay Quality I used lol ^^
Yes, it's much easier to check the quality using the formulas and material qualities while you're building.
However, it's also possible to use the output (bricks), to reverse engineer the quality of the structure. (The quality for bricks is [clay+clay+kiln+fuel]/4, if you know all the other items you should be able to figure out the quality of your kiln)
Plug in the previously provided formula for bricks, you should be able to find q10 anywhere, especially if you can find gray clay, and fuel should be easy as well.