Water makes up a large percentage of our body weight. Total body water (TBW) represents the sum of all fluid compartments in our body. Knowing your TBW can help you assess your hydration status and health. This article explains what TBW is, how to calculate it, and how to interpret the results.
What is Total Body Water?
Water is essential for life. It makes up 50-60% of our total body weight. Body water is contained both inside and outside cells in different compartments:
- Intracellular fluid (ICF) - Fluid inside cells (about 2/3 of TBW)
- Extracellular fluid (ECF) - Fluid outside cells (about 1/3 of TBW)
Total body water is the sum of intracellular and extracellular fluid. It depends on your age, sex, body fat percentage, and health status. Well-hydrated adult males have higher TBW (60-65% of weight) than females (50-60% of weight). Athletes also tend to have more TBW than less active people.
As we age, our body water percentages decrease. Fat tissue contains less water than muscle, so higher body fat levels also reduce TBW. Dehydration, illness, or muscle loss can quickly impact total body water.
How to calculate Total Body Water?
There are a few simple ways to estimate your total body water percentage at home:
Body weight method
Multiply your weight in kg by 0.6 if male, or 0.5 if female. This gives a rough estimate of TBW.
Body fat method
Subtract your body fat percentage from 100, then multiply the remainder by 0.73. This accounts for the lower water content of fat mass.
Watson formula
For males: TBW = 2.447 - 0.09156 × age + 0.1074 × height + 0.3362 × weight
For females: TBW = -2.097 + 0.1069 × height + 0.2466 × weight
where:
- age in years,
- height in centimeters,
- weight in kilograms.
Interpreting your Total Body Water results
The results of TBW calculations or body composition tests allow you to gauge your hydration status. Lower than normal TBW may indicate:
- Dehydration - Losing over 2% of TBW through sweat, urine, diarrhea, etc. can impact performance and health.
- Muscle loss - Since muscles are about 75% water, losing muscle also reduces TBW.
- Obesity - Excess fat tissue lowers TBW percentage due to its low water content.
Higher than normal TBW can sometimes result from edema or water retention due to illness, hormonal changes, certain medications, etc.
Tracking TBW over time provides insights into your hydration habits, body composition, and overall health. Aim to drink enough fluids daily to maintain normal total body water percentages for your age and sex. Consult a doctor for persistent high or low values.
Based on research by
- Watson PE, Watson ID, Batt RD. Total body water volumes for adult males and females estimated from simple anthropometric measurements. Am J Clin Nutr. 1980 Jan;33(1):27-39.
- Seoung Woo Lee, Joon Ho Song, Gyeong A Kim, Kyong Joo Lee, Moon‐Jae Kim Assessment of total body water from anthropometry‐based equations using bioelectrical impedance as reference in Korean adult control and haemodialysis subjects. Nephrology Dialysis Transplantation, Volume 16, Issue 1, January 2001, Pages 91–97.