How to use the free water deficit calculator
Estimate the free water deficit in a dehydrated patient from serum sodium and body weight. Enter body weight, serum sodium, total body water fraction in the fields above; the free water deficit is computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “free water deficit”, “hypernatremia water deficit”, “sodium water deficit”, “calculate free water deficit”, “find free water deficit”.
Formula
Variables
- w — Body weight (kg)
- na — Serum sodium (mmol/L)
- f — Total body water fraction
Worked example
With body weight = 70 kg, serum sodium = 155 mmol/L, total body water fraction = 0.6, the calculator gives free water deficit ≈ 4.5 L.
Frequently asked questions
What is the free water deficit calculator used for?
Estimate the free water deficit in a dehydrated patient from serum sodium and body weight. It helps with questions such as “free water deficit”, “hypernatremia water deficit”, “sodium water deficit”.
What is the formula for the free water deficit calculation?
Free water deficit (L) = f × w × (na / 140-1). Here w is body weight (kg), na is serum sodium (mmol/L), f is total body water fraction.
What inputs do I need for the free water deficit calculator?
You need body weight in kg, serum sodium in mmol/L, total body water fraction. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the free water deficit calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the free water deficit result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.