TBW/WT
Total Body Water to Weight (TBW/WT)
This value states what percentage of your body weight is made up of total body water.
Short answer
The water share of weight is mainly a picture of body composition. Water lives in fat free mass, so more fat means a lower water share. The manual gives a span of 50 to 70 percent and explains it precisely through the proportion of fat, not through fluid intake. Always read it alongside percent body fat.
What the value represents
The value comes from dividing total body water by weight. The manufacturer manual states that water makes up 50 to 70 percent of body weight, making it the single largest component of body composition.
The key point runs against most expectations: this value is not about fluid intake. Water is stored mainly in fat free mass — the manual puts it at roughly 73 percent of fat free mass — while fat tissue holds little of it. The water share of weight therefore largely tracks the share of fat free mass.
The manual illustrates this with the extremes: athletes with very low body fat reach up to 70 percent water, while people with a high proportion of fat sit around 50 percent. What separates them is not how much they drink but what their bodies are made of.
A lower water share therefore usually means a higher proportion of fat, not a shortage of fluid.
- The share of total body water in body weight, expressed as a percentage.
- An indirect picture of body composition — the larger the share of weight made up of fat free mass, the higher the water share.
- It does not represent hydration status or a recommended fluid intake.
- It says nothing about how water is divided between the inside of cells and their surroundings. That is described by the separate ECW Ratio.
How the value is produced
- A calculated value: total body water (L) ÷ weight (kg) × 100. A litre of water counts as a kilogram in this calculation.
- Total body water is not derived from weight — it comes from impedance measured at several frequencies, and the manufacturer presents it as a measured quantity rather than an estimate.
- Weight is measured directly by the built-in scale of the device.
- The manual gives no separate recommended range for this value. On the Evaluation Result Sheet it is instead accompanied by a T-score (comparison with a young age group) and a Z-score (comparison with the same age group) against the manufacturer reference data set.
How to read the current value
- The manual gives a general span of 50 to 70 percent of body weight and explains it through body composition: up to 70 percent in athletes with very low body fat, around 50 percent in people with a high proportion of fat.
- Always read the value alongside percent body fat. A low water share with a high fat percentage is the expected result, not a sign of insufficient fluid.
- The manual gives no recommended range for this value as it does for other metrics. On the evaluation sheet it is compared against the manufacturer data set through T- and Z-scores; that is a position within a reference set, not a clinical norm.
- The manual further notes that younger people tend to have more body water, which gradually declines with age, and that men tend to have more of it than women. It explains this by the difference in the amount of fat free mass, not by quality of hydration.
How to read change over time
- Short-term swings come mainly from the denominator. Food and drink change weight immediately, while body water distributes into tissues only with a delay — which is why the manual recommends measuring fasted.
- A sustained rise in the share alongside rising muscle mass and falling fat is expected. The water share goes up in that situation even if fluid intake never changed.
- A falling share alongside rising weight usually means fat mass rather than fat free mass is being added.
- Because both the numerator and the denominator can move, always look up total body water in litres and weight separately. Otherwise you cannot tell which side of the fraction shifted.
General principles: how to read change between measurements →
What to read it with
- Total body water in litres – the absolute value behind the share.
- Weight – the denominator, without which a change in the share cannot be interpreted.
- Percent Body Fat – the main reason the water share differs between people.
- Fat free mass – the component the water is mostly stored in.
- Hydration of fat free mass (TBW/FFM) – relates water only to the non-fat part of the body, so it is not distorted by the amount of fat.
- The ECW Ratio – adds the distribution information this share does not carry.
Common misunderstandings
- A low water share does not mean dehydration. It most often reflects a higher proportion of fat, because fat tissue contains little water.
- A higher water share does not mean water retention. Retention would show up as a shift in the ECW Ratio rather than in the water share of weight.
- You cannot meaningfully influence the value by drinking before the measurement. The fluid also raises the weight in the denominator, which is exactly why the manual recommends measuring fasted.
- The water share of weight is not the same as hydration of fat free mass. The first relates water to the whole of weight including fat, the second only to the non-fat part.
- The 50 to 70 percent span from the manual describes a population range, not a personal goal or a recommended range for a given individual.
What can affect the result short term
- Food and drink shortly before the measurement — stomach contents count towards weight and towards body composition.
- Training, sauna and showering before the measurement — they change perfusion and fluid distribution.
- Time of day and body position; the manual recommends standing for at least 5 minutes beforehand and repeating measurements under the same conditions.
- A full bladder — the water in it is not captured by the measurement, which according to the manual leads to overstated fat mass.
- Menstruation, during which body water fluctuates.
- Higher salt intake, alcohol the day before, illness and fever.
- Heavy clothing and jewellery, which raise the weight in the denominator.
What to do next
- Use the water share as a supplementary view of body composition, not as a check on fluid intake.
- When tissue hydration is what interests you, reach for hydration of fat free mass (TBW/FFM) and for the ECW Ratio. Those are built for it; this share is not.
- Follow the water share and percent body fat side by side. They move as mirrors of one another and make sense together, while separately they invite a wrong conclusion.
- Compare only measurements with the same preparation. The weight in the denominator responds to food and drink faster than the body water in the numerator.
What the value does not determine
- It does not establish hydration status or dehydration.
- It says nothing about how water is divided between the inside of cells and their surroundings.
- The manual gives no recommended range for it; the only comparison is a T- and Z-score against the manufacturer data set.
- It is sensitive to measurement conditions, because the weight in the denominator responds faster than body water.
- It shares the uncertainty of the bioimpedance estimate of total body water.
On terminology
- On the result sheet the value is labelled TBW/WT.
- The 50 to 70 percent span from the manual describes a population range, not a recommended range in the sense the manufacturer uses elsewhere.
In more depth, with sourcesIn more depth: why the water share of weight tracks the share of fat free massExpand the detailed explanation
InBody works with a molecular model in which weight = total body water + protein + minerals + fat mass, and fat free mass is the sum of the first three components. The manual adds that roughly 73 percent of fat free mass is water. From those two relationships it follows that the water share of weight is largely a restatement of the share of fat free mass: the larger the part of weight made up of non-fat tissue, the higher the water share. The extreme values the manual gives — up to 70 percent in athletes with very low body fat and around 50 percent in people with a high proportion of fat — are a direct consequence of that link, not a difference in fluid intake.
Methodologically it matters that the same assumption about the water content of lean tissue is also the basis from which bioimpedance estimates fat free mass in the first place. The ESPEN clinical guidelines on bioimpedance warn that in states with altered fluid distribution the assumption does not hold and body composition estimates shift. In such a situation the water share of weight is read more cautiously and always alongside the ECW Ratio, which shows whether water is distributed in the usual way.
On the Evaluation Result Sheet the value is compared against the manufacturer data set through T- and Z-scores. The manufacturer emphasises at the same time that this data affects only the evaluation and not the body composition analysis itself, and that chart settings can differ by country. These are therefore not clinical norms, and the scores must not be confused with the Z- and T-scores used in other fields.
The manual adds two pieces of physiological context: losing roughly 10 percent of body water has an immediate negative impact on the body, and an adult loses about 2.5 litres of water a day through breathing, sweat, urine and stool, so that much needs replacing. Both describe the need for water in general; they are not interpretive thresholds for this particular metric. The NIH consensus statement on bioimpedance further recalls that standardised conditions are decisive for comparing repeated measurements, which holds doubly for a value with weight in the denominator.
Sources
- InBody 970 Result Sheet Interpretation (ENG_A_211104) — InBody Co., Ltd.
- Bioelectrical impedance analysis in body composition measurement: NIH Technology Assessment Conference Statement — National Institutes of Health
- Bioelectrical impedance analysis – part II: utilization in clinical practice — Clinical Nutrition (ESPEN guidelines)
On this page
Related values
Related articles
Where to find it
The ECW Ratio Analysis and the separate Body Water result sheet.
- Reviewed by
- MojeInBody content team
- Date
An InBody measurement is not a diagnostic tool. Results do not determine health status and do not replace a medical examination.
FAQ
Frequently asked questions
Answers to what people ask most often about this value.
My water share is low. Does that mean I do not drink enough?
Usually not. Water is stored mainly in fat free mass, while fat tissue holds little of it. A lower water share therefore most often accompanies a higher proportion of fat. Check percent body fat from the same measurement — the answer is usually there.
Will drinking before the measurement raise my water share?
Not meaningfully. The fluid you drink also raises the weight in the denominator, and in the first moments it has not yet distributed into tissue. This is exactly why the manual recommends measuring fasted and repeating measurements under comparable conditions.
What water share is correct?
The manual gives no recommended range for this value. It gives only the general population span of 50 to 70 percent and explains it through the proportion of fat. On the evaluation sheet the value is compared against the manufacturer data set through T- and Z-scores, which is orientation within a reference set rather than a norm.
What is the difference between the water share and hydration of fat free mass?
The water share relates water to the whole of weight including fat, so it moves with the amount of fat. Hydration of fat free mass (TBW/FFM) relates water only to the non-fat part of the body, so it is not distorted by the amount of fat.
Explanations make the most sense alongside your own trend.
The public guide is open to everyone. The client portal adds your own value, history and the context of a specific measurement.