Enter the water uptake and body weight into the calculator to determine the Hydration Index. This calculator can also evaluate any of the variables given the others are known.

Hydration Index Formula

The following formula is used to calculate the Hydration Index.

HI = (WU / BW) 


  • HI is the Hydration Index (mL/g)
  • WU is the water uptake (mL)
  • BW is the body weight (g)

To calculate the Hydration Index, divide the water uptake by the body weight.

What is a Hydration Index?

A Hydration Index is a measure used to determine how well a beverage hydrates the body compared to a standard reference, usually water. It takes into account factors such as the volume of fluid intake, the drink’s nutrient composition, and the body’s fluid balance over a certain period after consumption. This index is useful in understanding the hydration effectiveness of different beverages, which can aid in maintaining optimal hydration levels for health and performance.

How to Calculate Hydration Index?

The following steps outline how to calculate the Hydration Index (HI).

  1. First, determine the water uptake (WU) in milliliters (mL).
  2. Next, determine the body weight (BW) in grams (g).
  3. Next, use the formula HI = (WU / BW) * 1000 to calculate the Hydration Index.
  4. Finally, calculate the Hydration Index.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Water uptake (WU) = 250 mL

Body weight (BW) = 500 g