BMI inputs
Choose US or metric units, then enter height and weight. Results update immediately and stay on this page.
Health calculator
BMI Calculator
Calculate body mass index from height and weight, then view the standard BMI category and a practical healthy-weight reference range.
Updated May 23, 2026No sign-in requiredDate, Time & Health calculator
Best used for
Quickly compare weight and height using a common screening metric.
Calculator inputs
Change any assumption and the result updates immediately.
BMI category
Healthy weight
Adult screening category
Healthy weight range
129-174 lb
Based on BMI 18.5 to 24.9
Height used
70.0 in
US units
Weight used
170.0 lb
US units
How to interpret BMI
BMI is a screening metric based on height and weight. It can be useful for a quick reference, but it does not measure body composition, fitness, or individual health risk.
BMI methodology
Metric BMI is weight in kilograms divided by height in meters squared.
- US BMI uses weight in pounds and height in inches with the 703 conversion factor.
- The category uses common adult BMI ranges: underweight, healthy weight, overweight, and obesity.
- Healthy-weight range is estimated from BMI 18.5 to 24.9 at the entered height.
BMI = weight kg / height m^2
US units: BMI = 703 x weight lb / height in^2
BMI example
A person who is 5 ft 10 in and weighs 170 lb has this BMI estimate.
Height
70 inches
Weight
170 lb
BMI
24.4
Category
Healthy weight
Understanding Body Mass Index
What BMI is and when people use it
Body mass index is a simple ratio of weight to height that sorts adults into broad categories: underweight, healthy weight, overweight, and obesity. Because it needs only two numbers, it has become a quick screening reference in clinics, fitness settings, and personal health check-ins.
People reach for BMI to get a fast, standardized snapshot, to estimate a healthy-weight range for a given height, or to have a clearer starting point for a conversation with a clinician. It is a screening signal, not a verdict on health.
How the BMI formula works
In metric units, BMI is weight in kilograms divided by height in meters squared. In US units, the same idea is expressed as 703 times weight in pounds divided by height in inches squared, where 703 simply converts the units so both formulas land on the same scale.
The math intentionally ignores everything except height and weight. That simplicity is what makes BMI easy to calculate anywhere, and also what creates its blind spots, since it cannot tell what the weight is actually made of.
Reading your BMI category
For many adults, a BMI from 18.5 to 24.9 is labeled healthy weight, below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above falls into the obesity range. These thresholds are population guidelines, not personal diagnoses.
A useful way to read the result is as a prompt rather than a conclusion. A number near a boundary, or one that surprises you, is a reason to look at other measures and context, not a reason to draw firm health conclusions on its own.
Common mistakes when interpreting BMI
A frequent error is treating BMI as a body-fat measurement. It does not distinguish muscle from fat, so a muscular, athletic person can land in the overweight range despite low body fat, while someone in the healthy range may carry more fat than the number suggests.
Another mistake is applying adult categories to people they were not designed for. Children, older adults, pregnant people, and some athletic or ethnic groups may need different references, so a single adult cutoff can mislead.
Practical ways to use BMI well
Pair BMI with other simple signals such as waist measurement, energy levels, activity, and how clothes fit. Looking at a few indicators together gives a fuller picture than any single number, and waist size in particular adds context BMI cannot.
Track trends over time rather than fixating on one reading. A gradual direction across months, alongside habits like sleep, movement, and nutrition, tends to be more meaningful than a single snapshot taken on one day.
What BMI does not capture
BMI says nothing about body composition, fat distribution, bone density, fitness, blood pressure, blood sugar, or genetics. Two people with identical BMIs can have very different health profiles, which is exactly why it is a screening tool and not a diagnostic one.
It also cannot account for individual medical history. Health risk is shaped by many factors that a height-and-weight ratio simply does not see, so BMI works best as one input among several.
A note on health decisions
This calculator is for general education and a quick reference. It does not provide medical advice, diagnose any condition, or recommend treatment, and it should not replace a professional assessment.
For decisions about weight, nutrition, or health risk, speak with a qualified healthcare professional who can consider your full history, run appropriate tests, and interpret results in the context of your individual situation.
Common Uses
- Quickly compare weight and height using a common screening metric.
- Estimate a healthy-weight range for a given height.
- Discuss weight categories more clearly with a qualified clinician.
Limitations and Assumptions
- BMI does not measure muscle mass, body fat percentage, pregnancy status, age-specific risk, or athletic build.
- BMI categories may not fit children, older adults, pregnant people, or some populations.
- This calculator does not diagnose health conditions.
Frequently Asked Questions
What is BMI?
BMI stands for body mass index. It compares body weight to height using a simple mathematical formula.
Is BMI a diagnosis?
No. BMI is a screening tool, not a diagnosis. Health risk depends on many factors beyond height and weight.
What BMI is considered healthy?
For many adults, a BMI from 18.5 to 24.9 is commonly categorized as healthy weight.
Why can BMI be misleading?
BMI can be misleading for people with high muscle mass, different body composition, pregnancy, or age-specific health considerations.
Does BMI work for children?
Adult BMI categories are not the right standard for children. Pediatric BMI should be interpreted using age- and sex-specific growth charts.
Can BMI measure body fat?
No. BMI uses only height and weight. It does not directly measure body fat, muscle mass, waist size, or metabolic health.
Should I make health decisions from BMI alone?
No. Use BMI as a quick reference only and discuss personal health decisions with a qualified healthcare professional.
Health disclaimer
This calculator is for general educational use only and is not medical advice. Health needs vary by age, sex, body composition, medical conditions, activity level, and professional guidance.
Built and maintained by Calculator Matters, an independent calculator project. Method checked against published formulas and primary sources · Educational estimate, not professional advice · How we calculate · Found an error? corrections@calculatormatters.com