Body water percentage: typical ranges, why scales vary, and how to measure it comparably

What is body water percentage?

Body water percentage is the share of your body weight that is water. Researchers calculate it by dividing total body water, in liters, by body weight, in kilograms.⁴ Water sits inside cells, around cells and in blood, and it is part of nearly every tissue.¹

Smart scales report this number. The Withings Body Comp page lists total body water percentage among its units, and the RENPHO Elis 1 page lists body water percentage among its 13 metrics.⁹¹⁰ Both estimate it from how easily a weak electrical current moves through the body, a method called bioelectrical impedance analysis. Impedance reflects the body’s water content, which is why it is used for this purpose.⁷

A scale cannot see inside you. It combines the impedance it measures with the age, height and sex you entered, then applies the maker’s equations. The result is an estimate of total body water. No manufacturer page read for this guide presents the figure as a test of how well hydrated you are right now.

What is a typical body water percentage?

The sources do not agree on one figure, and they should not be forced into one. Mayo Clinic says water makes up about 50% to 65% of your body weight.¹ Cleveland Clinic says an adult’s body is about 60% water.² MedlinePlus says water makes up more than two-thirds of the weight of the human body.³ The differences come from who was measured, how, and how the figure is rounded.

A study in Kidney Research and Clinical Practice measured 545 people aged 3 to 98 by bioelectrical impedance, which is the same family of method a home scale uses. In normal-weight males the percentage was about 62% from childhood through adult life and fell to 57% in the 61-and-older group. In normal-weight females it fell to 55% in the 11-to-20 group, stayed relatively stable through age 60, then fell to 50% in the oldest group. Overweight men and women had significantly lower percentages than normal-weight people.⁴

None of these pages gives a medical cutoff for “low” or “high” body water on a scale. RENPHO’s own explainer on what its scale measures does not give a normal range either.¹¹ That is worth knowing before you worry about a single reading.

Why does body water percentage differ between people?

Three factors show up in the study data. The first is sex. In the 545-person study, normal-weight women had a lower percentage than men from the teenage years on.⁴ The second is age. In both sexes the percentage was lower after age 60.⁴ The third is body fat. Overweight participants had significantly lower percentages than normal-weight participants.⁴

The practical consequence is that two healthy people can have quite different readings and both be typical for them. Comparing yourself with a friend, or with a single published percentage, says little. Comparing yourself with your own readings under the same conditions says much more.

Your body fat percentage and your muscle mass sit on the same measurement, so they move together with the water figure. For those, see the guides to body fat percentage and muscle mass. For the full picture of what a scale reports, see what is body composition.

How hydration changes the reading

Because impedance depends on body water, anything that shifts water shifts the reading. The studies below were done on healthy volunteers and, for the most part, on clinical or laboratory devices rather than home scales. They show the direction of the effects. They do not give you a correction factor.

Read together, the studies say two things. Your state at the time of the reading matters, and the effect on any one reading is usually modest. In the Deurenberg study, when conditions were standardized (morning, fasting, bladder emptied) the day-to-day variation within a person was 2.8 percent.⁵ A 2025 study of a clinical multi-frequency device in 1,000 healthy adults found high retest reliability for its device, and its background notes that such methods are reliable and moderately accurate only in tightly controlled conditions of food, hydration, recent exercise and time of day.⁸

A worked example: why the percentage moves when your weight does

Take a 160-pound person whose scale reports 55% body water. Water weight is 0.55 x 160 = 88 pounds. After a hot day the person loses 1.5 pounds, all of it water. The body now weighs 158.5 pounds and holds 86.5 pounds of water: 86.5 / 158.5 = 0.5457, or 54.6%. The percentage moved by less than half a point even though the person is mildly dehydrated. A scale that sees a different impedance, as the studies above suggest, could report a larger shift or a smaller one. This is arithmetic, not a measured result.

How to measure body water in a way you can compare

You cannot control everything, but you can control the conditions that you control. The routine below uses the manufacturers’ own instructions and the standardized conditions from the impedance study.

1. Weigh at the same time of day. RENPHO advises weighing at the same time each day, such as the morning.¹²
2. Follow the study’s standardized setup where you can: in the morning, fasting, after emptying your bladder.⁵
3. Avoid heavy exercise beforehand. RENPHO says measurements may not be accurate after heavy physical activity, and the Deurenberg study found strenuous exercise lowered impedance.⁵¹²
4. Step on with bare, dry feet, both on the electrode plates. Both RENPHO and Withings say not to step on with wet feet.¹²¹³
5. Use a hard, flat surface. RENPHO says softer floors such as carpet can cause inaccuracies.¹²
6. Keep your drinking routine steady on the evening before and the morning of the reading, so the same amount of fluid is in play each time.
7. Compare weekly averages. RENPHO says trends matter more than the absolute value of a single measurement.¹²

Athletes and pregnancy need extra thought. RENPHO’s FAQ says adults who are athletes should turn on Athlete Mode, noting that athletes can have higher bone density and hydration levels.¹² The Withings guide warns that accuracy of the body composition analysis may be affected in pregnancy, and that the scale should not be used with a cardiac pacemaker, an implantable cardioverter-defibrillator or other implanted electronic devices.⁹¹³ Ask a clinician if either applies.

What a scale’s body water number does not tell you

• Where the water is. The studies split water into intracellular and extracellular, but a home scale usually shows only a total percentage.⁶⁹¹⁰
• Whether you are dehydrated. The studies show hydration shifts the reading; they do not make the reading a hydration test.⁶⁷
• A diagnosis of any condition. A scale gives estimates for tracking trends. Questions about swelling, unusual thirst or fluid intake belong with a clinician.
• A target to chase. No source read sets a pass-or-fail body water percentage, and the sources differ on the average.¹²³

A smart scale is more useful as a trend tool. If your body water reading drifts steadily over several weeks while your routine stays the same, that is a pattern worth noting. If it jumps on one morning after a salty dinner or a hard workout, it probably says more about the dinner or the workout.

To compare brands before buying, see Withings vs Renpho. To understand the limits of home scales more broadly, read are smart scales accurate and the best time to weigh yourself.

Frequently asked questions