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Introduction: There are limited data on how stone factors relate to flexible ureteroscopy (f-URS) laser lithotripsy efficiency and outcomes when using the Moses Technology Ho:YAG system. We examined the relationship of stone volume and density to lithotripsy, lasing times, and energy used to treat a single renal stone. We also assessed short-term clinical outcomes. Methods: We analyzed patients undergoing f-URS by a single surgeon using high-power Moses Technology Ho:YAG system (Lumenis). We only included cases with a CT confirming a solitary renal stone. Ureteral stones, staged and bilateral procedures were excluded. Stone dimensions and HU were obtained. Volume (mm 3 ) was calculated using European Association of Urology criteria. Laser energy (J), lithotripsy, and lasing times were obtained. Laser activity was calculated by dividing lasing time by lithotripsy time. Relationships between time, stone density, volume, and energy were assessed using Spearman correlation. Complications were assessed using Clavien-Dindo grade. Residual fragments (RF) were determined on imaging within 3 months. Results: Twenty-nine patients met the inclusion criteria. Mean (range) stone volume and density were 290 mm 3 (42-1700) and 814 HU (170-1675), respectively. Mean lithotripsy and lasing times were 11.9 (3.6-26.0) and 6.0 (0.6-19.6) minutes, respectively. Mean laser activity was 47%. Mean fragmentation speed was 0.9 mm 3 /s. Mean energy used per unit stone volume was 38.2 J/mm 3 . Time taken to perform fragmentation had a stronger association with the stone volume vs stone density. Three (10.3%) and 2 (6.9%) patients had a Clavien Grade 1 and 2 complications, respectively. At follow-up the zero-fragment rate was 79.3%. Conclusions: When using the Moses Technology laser to ablate a single renal stone with f-URS, the fragmentation speed was ∼1 mm 3 /s. Stone volume, not density was correlated to lasing time. We propose mm 3 /s be considered a measure that has implications for technique efficiency and comparing laser platforms.