Insensible Water Loss Calculator

Estimate insensible water loss in ml/hr and ml/day for adults, children, infants, or burn patients from weight, height, fever, and burned body surface.

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Insensible Water Loss Formula

The following formula is used to calculate the insensible water loss for a given body surface area and insensible water loss rate.

IWL = BSA * IWL_R

Formula source: The Philadelphia Guide: Inpatient Pediatrics, 3e (McGraw Hill Medical)

Variables:

IWL is the insensible water loss (ml/day)
BSA is the body surface area (m²)
IWL_R is the insensible water loss rate per body surface area (ml/m²/day)

To calculate the insensible water loss, multiply the body surface area by the insensible water loss rate per body surface area.

What is Insensible Water Loss?

Insensible water loss refers to the amount of fluid lost from the body through processes that are not easily measured, such as evaporation from the skin and respiratory tract. Unlike sensible water loss, which includes measurable losses like urine and sweat, insensible water loss occurs continuously and is influenced by factors such as ambient temperature, humidity, and physical activity. It is an important consideration in medical and physiological contexts, particularly in the management of fluid balance in patients.

How to Calculate Insensible Water Loss?

The following steps outline how to calculate the Insensible Water Loss.

First, determine the body surface area (BSA).
Next, determine the insensible water loss rate per body surface area (IWL_R).
Finally, calculate the insensible water loss using the formula IWL = BSA * IWL_R.
After inserting the values 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.

Body Surface Area (BSA) = 1.8 m²

Insensible Water Loss Rate per Body Surface Area (IWL_R) = 400 ml/m²/day