Hydration Status from Urine Calculator

How it is calculated

The tool turns urine specific gravity into an approximate osmolality with a simple rule of thumb:

osmolality (mOsm/kg) ≈ (SG − 1) × 1000 × 35

In other words, take the last digits of the specific gravity (1.020 gives 20) and multiply by 35. SG is entered as a decimal such as 1.020 and must be above 1.000 and below 1.060; anything outside that range, or a whole number such as 1020, returns no result. The result is shown in mOsm/kg with two decimals. The tool gives only the osmolality estimate, not a hydration category, so you need to compare it with the reference ranges of your own lab or coach. The 35 factor is an approximation, and glucose or protein in the urine, which raise specific gravity more than osmolality, can make it less accurate.

Common mistakes

• Typing the reading without the decimal point (1020) or only the last digits (20). The tool expects the full value such as 1.020 and returns no result otherwise.
• Using a test strip colour or a urine colour chart reading in the SG field. The input is the numerical specific gravity from a refractometer or strip.
• Measuring after a large drink or heavy exercise and treating it as a usual state. A single reading changes through the day, so a first-morning sample is more consistent.
• Using the estimate for a person with glucose or protein in the urine, such as in uncontrolled diabetes. Those substances raise SG more than osmolality.
• Mixing osmolality units. The result is in mOsm/kg, and lab results in mmol/kg are numerically similar but should be checked against the lab's units.