Kidney stone of 12mm size?

See Urology: If symptomatic need to se urology ; may need intervention depending upon the location. If recurrent to see a nephrologist for special testing and treatment. Meanwhile increase water intake if ok to do based on other medical or health problems and low sodium diet.

Yeah, that's big.: A stone up to 5mm in size will predictably pass, with variable degrees of pain. A 12mm stone is going to get stuck if it decides to move out of the kidney. You should get that stone managed before it starts to move.