Estimate insensible water loss from body weight or body surface area using typical adult (10 mL/kg/day) or child (400 mL/m²/day) rates, or your own.

10 mL/kg/day is a common adult estimate. Use Custom for a clinician-selected rate.

Optional settings
Blank means no adjustment. No automatic fever correction is applied.

Related Calculators

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 × IWLR

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)
  • IWLR is the insensible water loss rate per body surface area (ml/m²/day)

For the BSA method, multiply BSA by your supplied baseline rate in mL/m²/day. Alternatively, use weight × supplied mL/kg/hour rate × 24. A clinician must choose the rate for the patient and conditions. Height and weight can estimate BSA using the Mosteller approximation: BSA (m²) = √(height in cm × weight in kg / 3600). The optional percentage is an entered assumption, not an automatic fever correction. This estimates insensible loss only and cannot determine an individual fluid prescription.

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.

  1. First, determine the body surface area (BSA).
  2. Next, determine the insensible water loss rate per body surface area (IWLR).
  3. Finally, calculate the insensible water loss using the formula IWL = BSA * IWLR.
  4. 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

Illustrative supplied rate (IWLR) = 400 mL/m²/day. With no additional adjustment, 1.8 × 400 = 720 mL/day, or 30 mL/hour. This example rate is not a recommendation for all adults, children or infants.