Value comparison
ECW/TBW ratio vs. total body water
Short answer
Total body water tells you how many litres of water you carry, while the ECW/TBW ratio describes how that water is split between the inside of your cells and the space around them.
Side by side
| Aspect | ECW RatioECW/TBW | Total body waterTBW |
|---|---|---|
| What it measures | The share of water outside cells within total body water, i.e. the distribution of water. | The total volume of water in the body, the sum of water inside and outside cells. |
| How it is produced | Calculated from measured volumes: ECW Ratio = ECW / TBW. | Derived from the measured impedance; the manufacturer presents it as a measured quantity rather than an estimate. |
| Unit | dimensionless ratio | litres |
| Manufacturer reference range | 0.360–0.390. The evaluation sheet adds: Normal below 0.390, Slightly Over 0.390–0.400, Over above 0.400. | An individual range is printed in brackets next to the value; the manual gives no general formula for it. |
| Where on the sheet | The ECW Ratio Analysis section; marked ECW/TBW on the research sheet, with a segmental variant per body part. | The first row of Body Composition Analysis; the body water sheet breaks it into water inside and outside cells. |
| When to use it | When checking whether muscle mass is overstated by retained water, or when following swelling. | When following hydration and the comparability of conditions between measurements. |
| What it cannot tell you | It cannot identify a cause or any diagnosis; the manual notes raised ratios in slim women, older adults and people with obesity without any specific diagnosis. | It cannot say whether the water sits inside or outside cells — that is precisely what the ratio is for. |
When the values diverge
- After heavy drinking or a salty meal total water can rise without the ratio moving much, because water is added to both compartments.
- With swelling the water outside cells rises faster than the total volume, so the ratio climbs even when the litres stay flat.
- After muscle gain total water rises thanks to water inside cells, so the ratio may actually drift slightly down.
- With dehydration the litres fall while the ratio stays inside the range, because water is lost from both compartments.
The most common wrong conclusion
Reading more litres of water as "retention". Retained water shows up as a shifted ECW/TBW ratio, not as a larger absolute volume — which naturally grows with muscle mass.
Full explanations of each value
Related articles
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
Does a higher ECW/TBW ratio mean I have swelling?
Not on its own. The manual notes that slim women, older adults and people with little muscle can show a raised ratio without any specific diagnosis. It is a signal to read muscle values more carefully and follow the trend, not a conclusion about health status.
Why do I have a lot of body water yet a normal ratio?
Water volume naturally grows with muscle mass — the manual states that roughly 73 % of fat free mass is water. What answers the retention question is the distribution, that is the ratio, not the absolute litres.
Which value is more sensitive to a single measurement?
Total water in litres fluctuates routinely with drinking, food, exercise and time of day. The ratio is steadier, which is exactly why it is read as a control value alongside muscle mass and the segmental analysis.
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.