General Wellness
The everyday measurements that give a picture of overall health.
Some health numbers do not belong to a single organ system: resting heart rate, sleep duration, activity level, weight trend and waist measurement together sketch a general picture. Their value is mostly in their trend rather than any single reading, and in how they change together. This hub collects the measurements worth understanding even when nothing is wrong, alongside a realistic account of what each can and cannot tell you.
General Wellness tools
Calculators and converters for the measurements in this area.
BMI
General Wellness
Calculate body mass index in feet and pounds or metric units, with its real limits explained.
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Blood Pressure
Heart Health
See which guideline category a blood pressure reading falls into.
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Heart Rate Zones
Fitness
Estimate training heart rate zones from your age and optional resting heart rate.
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Waist-to-Height
General Wellness
Divide your waist by your height and read the result against the bands NICE publishes.
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Waist-to-Hip
General Wellness
Compare your waist and hip measurements against the cut-points in the WHO expert consultation.
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Body Fat %
Fitness
Estimate body fat from tape measurements with the Hodgdon–Beckett circumference equations.
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Body Surface Area
General Wellness
Calculate body surface area with four published equations, and see how far apart they land.
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Ideal Body Weight
General Wellness
Compare the Devine, Robinson, Miller and Hamwi equations — and see how much they disagree.
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Water Intake
Nutrition
See the US and European reference values for water side by side, rather than one invented number.
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General Wellness guides
Plain-English explanations of what these measurements mean.
FitnessBody Fat Percentage and the Navy Tape Method: How Accurate Is It?
The tape-measure method used by the US military estimates body fat from neck, waist and height, and hip for women. It is typically accurate to within three to four percentage po…
8 min read
NutritionHow Much Water Do You Need Each Day? What the Numbers Mean
US and European reference values for daily water intake differ by roughly a liter, they count water from food and every beverage, and thirst is a workable guide for most healthy…
8 min read
Blood TestsLiver Function Tests Explained: What ALT and AST Results Mean
ALT and AST are enzymes that leak into the blood when liver cells are irritated or damaged. A raised result is a prompt to look for a cause, not a diagnosis, and a result inside…
8 min read
SleepSleep Stages Explained: Light, Deep and REM Sleep
Sleep cycles through NREM stages and REM sleep, each defined by brain and muscle activity. Understanding what the stages are, and why a wrist device can only estimate them, help…
7 min read
General WellnessWaist Circumference, Waist-to-Height and Waist-to-Hip Ratio Explained
Where weight is carried says something that BMI cannot. Waist circumference, waist-to-height ratio and waist-to-hip ratio each measure central fat in a different way, with cut-p…
8 min read
Diabetes & Metabolic HealthBlood Glucose Units Explained: mg/dL, mmol/L and A1C in mmol/mol
The same glucose result can be written in mg/dL or mmol/L, and A1C in percent or mmol/mol. The conversions are exact arithmetic, but they change how a number is written, not wha…
7 min read
Heart HealthCholesterol Units Explained: mg/dL vs mmol/L and Why Triglycerides Differ
US labs report cholesterol in mg/dL and most other countries use mmol/L. Cholesterol and triglycerides have different conversion factors, 38.67 and 88.57, and using the wrong on…
7 min read
General WellnessIdeal Body Weight Formulas: Where Devine, Robinson, Miller and Hamwi Came From
The four ideal body weight equations in common use were written to size drug doses, not to say what weight is healthiest. They disagree by several kilograms at the same height,…
7 min read
Heart HealthHow to Measure Blood Pressure at Home Accurately: A Step-by-Step Guide
Posture, rest, cuff size and timing change a home blood pressure reading by enough to alter how it is classified. Here is the measurement routine the American Heart Association…
7 min read
Kidney HealthBody Surface Area Formulas: Mosteller, Du Bois, Haycock and Why They Differ
Body surface area scales drug doses and kidney measurements such as eGFR. Four published equations estimate it, they agree closely at average size and diverge at higher body wei…
7 min read
General WellnessBMI Categories Around the World: WHO, CDC and the Asian Action Points
The adult BMI categories used by the WHO and the CDC are the same, but the WHO has also suggested additional action points at 23.0 and 27.5 for some Asian populations. Here is h…
7 min read
General WellnessHow to Judge an Online Health Calculator: A Checklist for Readers and Clinics
A health calculator is only as trustworthy as its equation, its limits and what it does with your data. This checklist shows how to tell a transparent tool from a risky one, wit…
8 min read
SleepHow Much Sleep Do Adults Actually Need?
Seven or more hours a night is the figure US sleep and public health bodies converge on for adults. It is a floor rather than a target, the evidence behind it is associative, an…
8 min read
SleepWhat Sleep Trackers Actually Measure
A wrist tracker measures movement and pulse, then infers sleep from them. Total sleep time comes out reasonably well; the stage percentages are estimates from an algorithm that…
8 min read
Women's HealthIron, Hemoglobin and Ferritin: Why the Ranges Differ for Women
Hemoglobin reference ranges are lower for women and ferritin ranges differ too, largely because menstrual blood loss makes iron deficiency far more common before menopause. Ferr…
8 min read
Women's HealthWhich Health Calculators Do Not Apply During Pregnancy
Pregnancy changes blood volume, kidney filtration, red cell turnover and energy requirements, and most everyday health equations were derived in people who were not pregnant. He…
8 min read
Heart HealthUnderstanding Blood Pressure Numbers
The top number is the pressure as your heart contracts, the bottom number is the pressure between beats. In the United States the categories come from the 2025 AHA/ACC guideline…
13 min read
General WellnessWhat Is BMI and What Does It Actually Tell You?
BMI is weight divided by height squared — a population screening tool invented in the 1830s, not a measure of an individual’s health. It cannot distinguish muscle from fat, says…
10 min read
Heart HealthWhat Is a Normal Resting Heart Rate?
A resting heart rate of 60 to 100 beats per minute is the commonly cited adult range, though trained athletes often sit well below it. What matters more than the absolute number…
7 min read
NutritionBMR vs TDEE: Understanding Daily Calorie Needs
BMR is the energy your body uses at complete rest; TDEE adds everything else you do. Both are predicted from equations rather than measured, and the predictions carry a margin o…
8 min read