If the size of both kidneys is 8cm and the kidney function is normal, it is normal. If the size of both kidneys is 8cm but the kidney function is abnormal, it is abnormal and may be caused by kidney disease. To determine whether the size of both kidneys 8cm is normal or not needs to be based on the actual situation and cannot be generalized, it mainly depends on whether the kidney function is abnormal or not. Under normal circumstances, the length, width and thickness of adult kidneys are 10.5-11.5cm, 5-7.2cm and 2-3cm respectively. if the size of both kidneys is 8cm and there is no abnormality in kidney function, it is normal. It is mainly because the size of kidneys is related to gender, congenital development and other factors, and there is obvious individual variability. However, if the size of both kidneys is 8cm and there are abnormalities in renal function, the size of both kidneys is not normal, and you need to consider that it may be caused by chronic pyelonephritis, secondary glomerulonephritis and other renal diseases. To summarize, the size of both kidneys 8cm is not necessarily normal, you need to go to the hospital to test the renal function and so on, to clarify the specific situation.