Bladder ultrasound

volume = length x width x heigth x 0.52

Source

Arch Ital Urol Androl. 2005 Mar;77(1):60-2. Measurements of urinary bladder volume: comparison of five ultrasound calculation methods in volunteers. Dicuio M, Pomara G, Menchini Fabris F, Ales V, Dahlstrand C, Morelli G.