There are 8 fluid ounces in a cup.
What planet are you on? I don't mean to be a wise-ass, but weight depends upon the acceleration of gravity, which is different on different planets, whereas mass is the same no matter where you are. On the surface of the Earth, the acceleration due to gravity is 9.8 m/s2, so a 40-kg mass will weigh 40 x 9.8 = 392 newtons.
1 US fluid ounce = 29.5735297 milliliters (about 30 mL). Millimeters are a measurement of length liquid ounces are a volume the two do not compute with each other, However the following does work with milliliters.
1 US fluid ounce = 29.5735296 milliliters One fluid ounce equals 2 TBS, 8 drams, 30cc, or 30ml. hope it helps. - medical student