Volume should be used instead of diameter for kidney stones between 10 and 20 mm to determine the type of surgery and increase success.

Aim of this study is to categorize stones between 10 and 20 mm according to stone diameter or volume and compare mini percutaneous nephrolithotomy (mPNL) and retrograde intrarenal surgery (RIRS) outcomes. Files of 515 patients who underwent surgery for kidney stones with sizes 10-20 mm were reviewed. Patients were divided into RIRS or mPNL groups. An attempt was made to find the diameter and volume threshold values above which the success of the operation, complication rates and the number of auxiliary treatments deteriorated. Subgroup analysis was performed below and above the threshold value to reveal the optimal treatment methods. RIRS complications increased with volumes above 1064 mm 3 , number of auxiliary interventions increased with volumes above 1256 mm 3 , and success of the operation decreased with volumes above 1416 mm 3 . A subgroup analysis under and over 1064 mm 3 was performed in RIRS group. Complication and auxiliary treatment rates were higher, operative success was lower in patients with a stone volume greater than 1064 mm 3 . In patients who underwent RIRS, for every 1000 mm 3 increase in stone volume success of the operation decreased by 2.1 times, while the probability of auxiliary treatment increased by 2.8 times. In patients with kidney stones between 10 and 20 mm, it is more meaningful to use volume instead of diameter to determine the success rate. When mPNL is used instead of RIRS for volumes greater than 1064 mm 3 , the success rate will be higher, complication rate will be similar, and the need for auxiliary treatment will be lower.