The specific gravity of a fluid is the weight of the fluid relative to that of an equal volume of a reference substance, typically water. It is related to the density (weight per volume) of the fluid. If the weight and specific gravity of a urine sample are known, then the volume can be calculated.
specific gravity of fluid =
= (weight in grams of 1 mL of fluid) / (weight in grams of 1 mL of water)
where:
• The weight of 1 gram of water at 0°C and 1 atmosphere is 1 gram (0.99987). At room temperature (70°F) it is about 0.998 grams. To keep the calculations simple I will use 1 gram for the weight of 1 mL of water.
weight of fluid sample in grams =
= (weight of fluid filled container) – (weight of container empty)
volume of fluid in mL =
= (weight of fluid sample in grams) / (specific gravity of fluid)
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