Body Fluid Balance Calculator
Calculates net 0.9% saline–equivalent and free-water balance from recorded inputs and outputs.
Enter every amount as a positive number in mL. The calculator applies a negative sign to body-fluid losses automatically. For urine, TPN, other body fluid, and other enteral solution, enter the measured or prescribed sodium concentration when volume is recorded.
Calculated balance
Positive values indicate a net gain; negative values indicate a net loss.
Net 0.9% saline equivalent
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Net free water
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Recorded fluid balance
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| Source | Recorded mL | [Na⁺] used (mEq/L) | 0.9% saline equivalent (mL) | Free water (mL) |
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Calculation method
For standard inputs: 0.9% saline equivalent = volume × [Na⁺] ÷ 154. Free water = volume − saline equivalent. Losses are reported as negative values.
Packed RBCs use the specified 2.8 mL 0.9% saline equivalent per 1 mL pRBC, with free water set to 0 mL.
Clinical decision-support only. Confirm all fluid volumes, sodium concentrations, product formulations, and local protocols; do not use this calculation as the sole basis for patient management.
