Calculate BMI with consistent units
Body mass index compares weight with height squared:
BMI = weight in kilograms ÷ height in meters²
The equivalent customary-unit calculation is approximately 703 × weight in pounds ÷ height in inches². Convert feet and inches into total inches first. For example, 5 feet 10 inches is 70 inches, not 5.10 feet.
At 72 kilograms and 1.75 meters, BMI is 72 ÷ 1.75², or approximately 23.51 kg/m². The formula is arithmetic; interpreting it requires context.
Understand the adult screening categories
| BMI | CDC adult category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to below 25 | Healthy weight |
| 25 to below 30 | Overweight |
| 30 or above | Obesity |
These categories apply to adults age 20 and older. Children and teenagers use age- and sex-specific assessment rather than simply applying this adult table. The terms are screening categories, not descriptions of a person’s worth or proof of a diagnosis. [1]
The BMI categories in this guide apply to adult screening. They are not a pregnancy weight-gain framework or a pediatric growth assessment.
Why a category is not a complete health assessment
BMI does not distinguish fat from muscle and other lean tissue. It also does not describe where fat is distributed. Two people with the same height and weight can have different body composition and health circumstances. [2]
A result within the “healthy weight” category does not rule out a medical concern. A result outside it does not establish that a particular treatment or weight-loss plan is appropriate. Health history, examination, blood pressure, laboratory information when indicated, and other factors can matter.
Avoid turning a single calculator result into an “ideal weight” command. A clinically appropriate goal depends on the individual and the purpose of the assessment.
Measurement and rounding can change a borderline result
Measure height and weight consistently and check the entered units. A pounds-versus-kilograms mistake produces a much larger error than an extra decimal place can fix.
Near a category boundary, rounding can make a displayed value look as if it belongs in the adjacent category. Use the unrounded calculation for categorization, but do not treat a tiny crossing as a sudden transformation in health.
Day-to-day weight variation can reflect fluid and other short-term changes. A trend measured under comparable conditions is usually more interpretable than repeatedly reacting to one isolated reading.
Use BMI alongside the question you actually have
For a fitness goal, strength, endurance, recovery, and training progress may answer questions BMI cannot. For a clinical concern, a healthcare professional can decide which additional measurements are relevant. For nutrition concerns, intake, symptoms, and changes over time can be more informative than a category label alone.
A person with unexplained weight change, restrictive eating concerns, pregnancy, or a condition affecting body composition should not rely on a generic adult calculator to choose a target. Seek individualized guidance rather than intensifying diet or exercise to move the number.
What to do with the result
Record the input values and understand the category. Then ask whether there is a specific health concern that needs evaluation. A calculator can organize information for that conversation, but it cannot diagnose disease or determine treatment.
Use the related guide on BMI limitations to understand alternatives without assuming that another single number is a perfect replacement. The goal is a more complete assessment, not finding whichever metric supplies the most reassuring label.
Frequently asked questions
Is BMI a direct body-fat measurement?
No. It is calculated from height and weight and does not distinguish fat from muscle or other lean tissue.
Can children use the adult BMI categories?
No. Children and teenagers require age- and sex-specific growth assessment rather than direct use of the adult category table.
Does a healthy-weight BMI guarantee good health?
No. It is one screening result. Symptoms, medical history, body composition, and other relevant measurements still matter.
Sources & calculation notes
Primary references are linked below. Dates, limits, and product terms can change; confirm the applicable details before acting.
Use this guide thoughtfully. Educational information, not a diagnosis or individualized medical advice. A screening result or formula cannot establish what is safe or appropriate for a particular person. Consult a qualified healthcare professional for clinical decisions.