Calculator Inputs
Formula Used
TBW = body weight × total body water fraction
ECF water = TBW × extracellular fraction
ICF water = TBW − ECF water
TBW sodium pool = sodium concentration × TBW
ECF sodium = sodium concentration × ECF water
ICF sodium = ICF sodium concentration × ICF water
Modeled total body sodium = ECF sodium + ICF sodium + structural reserve sodium
Target change = TBW × (target sodium − current sodium)
Grams sodium = mmol × 22.98976928 ÷ 1000
Salt equivalent = mmol × 58.44277 ÷ 1000
How to Use This Calculator
- Select a body water profile or enter a custom water percentage.
- Enter body weight and choose kg or lb.
- Enter sodium concentration in mmol/L or mEq/L.
- Set extracellular water fraction and ICF sodium if needed.
- Add exchangeable and reserve factors for advanced modeling.
- Enter a target concentration to estimate the modeled change.
- Press Calculate to view results above the form.
- Use CSV or PDF export for reports and class records.
Example Data Table
| Case | Weight | TBW % | Sodium | TBW | TBW Sodium Pool | Sodium Mass |
|---|---|---|---|---|---|---|
| Adult male model | 70 kg | 60% | 140 mmol/L | 42.00 L | 5,880 mmol | 135.18 g Na |
| Adult female model | 60 kg | 50% | 138 mmol/L | 30.00 L | 4,140 mmol | 95.18 g Na |
| Older adult model | 80 kg | 45% | 142 mmol/L | 36.00 L | 5,112 mmol | 117.57 g Na |
Understanding Total Body Sodium
Total body sodium is the modeled amount of sodium in the body. Sodium is a major extracellular ion. It supports osmotic balance, water distribution, and electrical gradients. A chemistry calculator cannot measure body stores directly. It estimates pools from weight, water fraction, and sodium concentration. That makes the result useful for study, teaching, and quick comparison.
Why Body Water Matters
Most measured sodium is reported as a concentration. The usual unit is millimoles per liter. A concentration becomes an amount only after it is multiplied by volume. Total body water supplies that volume estimate. The calculator lets you choose a profile or enter a custom water percentage. This is important because water fraction changes with body size, age, sex, and composition.
Compartment Modeling
The extracellular compartment contains the highest sodium concentration. The intracellular compartment has much lower free sodium. For this reason, the tool separates total body water into extracellular and intracellular water. It then multiplies each compartment by its selected sodium concentration. You can also add a structural reserve factor. This optional term represents sodium linked with bone and other less exchangeable stores.
Interpreting the Outputs
The main result is a modeled sodium amount in millimoles. The calculator also converts that value to grams of elemental sodium. It gives a sodium chloride equivalent for comparison. These conversions use molar mass. They do not mean the body contains all sodium as table salt. The target change line estimates a sodium gap from a chosen target concentration. Positive values suggest added dissolved sodium would be needed in the model. Negative values show the model is above the target.
Use and Limits
Use this calculator for chemistry practice and educational planning. Check every input before trusting the result. Small changes in body water create large changes in sodium amount. The equations are simplified. Real human physiology includes hormones, kidney function, proteins, and nonexchangeable stores. This page is not a diagnostic tool. It should not guide treatment, fluid therapy, or diet changes. For health decisions, use professional clinical advice.
Good records improve repeat use. Save each result with its assumptions. Compare examples with equal units. This helps learners see which input drives the largest change in the final amount.
FAQs
What does total body sodium mean?
It means the estimated amount of sodium in body compartments. This calculator models sodium from water volume, concentration, and optional reserve factors.
Is mmol/L the same as mEq/L for sodium?
Yes. Sodium has a charge of plus one. For sodium ions, 1 mmol/L equals 1 mEq/L.
Why does body water percentage matter?
Sodium concentration is measured per liter. Body water estimates the volume. A higher water percentage gives a larger sodium pool.
What is the ECF fraction?
ECF fraction is the share of total body water outside cells. Sodium is mainly extracellular, so this value strongly affects compartment results.
What is the ICF sodium value?
It is the selected sodium concentration inside cells. It is much lower than extracellular sodium in this simplified model.
What is structural reserve sodium?
It is an optional estimate for sodium linked with less exchangeable stores. It helps create a broader chemistry model.
Can this guide medical treatment?
No. It is an educational calculator. It should not guide diagnosis, fluid therapy, diet plans, or medicine decisions.
Why export CSV or PDF?
CSV is useful for spreadsheets. PDF is useful for reports, assignments, and saved chemistry calculations.