How Long Do Kidney Stones Take To Pass What To Expect In our study, the stonefree rate for kidney stones > 40 mm dropped down to 67% after a mean 18 session, compared with a 100% stonefree rate for stones 40 mm after a mean 13 session Therefore, in our opinion, the percutaneous approach should be considered to be a preferred option for stones larger than 40 mmThe SFR for stones in the renal pelvis, lower, middle, and upper calices were 724, 56, 556, and 69%, respectively, whereas that for stones 1 cm, 11 to 2 cm, and 005) The author concluded that stone burden rather than stone location is a more important predictor of the outcome of SWL How long to pass 1 mm kidney stone