BMI Calculator - Body Mass Index for Adults

A BMI calculator answers one screening question: given standing height and current body weight, what is the body mass index, and which WHO adult category does that number fall into? The formula is the Quetelet index BMI = weight (kg) / height (m)². The default inputs on this page are 175 cm and 70 kg, which is 70 / 1.75² ≈ 22.86, inside the WHO normal band of 18.5–24.9. Imperial entries are converted with 1 inch = 2.54 cm and 1 pound = 0.45359237 kg, then the same SI formula runs. Equivalently, BMI = 703 × lb / in²; this implementation prefers kg/m² so metric and imperial stay consistent.

BMI is popular because it needs only two cheap measurements and because large epidemiology studies already tabulate population risk against those bands. It is also easy to misuse. The index does not measure fat, muscle, bone, waist, visceral adipose tissue, blood pressure, glucose, or fitness. A powerlifter and a sedentary office worker can share a BMI of 28 and have very different cardiometabolic profiles. This page therefore labels the WHO band as a screening category, not a disease name.

Scope is adult and non-pregnant. Children need age- and sex-specific percentiles (CDC or WHO growth charts). Pregnancy needs obstetric weight-gain guidance, not a pre-pregnancy BMI slapped onto a third-trimester scale reading. If you want the weight interval that keeps BMI between 18.5 and 24.9 for a height without entering today’s weight, use the healthy weight calculator. If you already know BMI and want the overweight/obesity cutoffs highlighted, use the overweight calculator. Underweight and thinness grades are covered on the underweight BMI calculator. None of those pages diagnose an eating disorder.

This is not medical advice. A clinician may still use BMI as one input among waist circumference, history, labs, and medications. Some health systems apply lower overweight thresholds for people of Asian ancestry (often 23 and 25 instead of 25 and 30) because type 2 diabetes risk can rise at a lower BMI. This calculator reports the global WHO adult table and does not silently switch ethnic cutoffs. If your clinic uses a different table, follow the clinic.

1. Choose metric (centimetres and kilograms) or imperial (feet, leftover inches, and pounds).
2. Enter current standing height and a recent weight. Morning weight after voiding is more repeatable than a post-meal reading, but any consistent protocol is better than mixing protocols.
3. Read BMI, the WHO adult category, and the 18.5–24.9 weight band at that height. Copy the result if you need a record.
4. Treat the category as a conversation starter, not a prescription. Inputs stay in this browser for up to 30 days and are never uploaded.

Convert 175 cm to 1.75 m. Square the height: 1.75 × 1.75 = 3.0625 m². Divide 70 kg by 3.0625: BMI = 22.857…, displayed as 22.86. WHO normal starts at 18.5 and stops just below 25, so 22.86 is unambiguously normal on that table. The matching healthy weight interval is 18.5 × 3.0625 = 56.66 kg through 24.9 × 3.0625 = 76.26 kg. Those bounds move only with height, not with today’s weight.

Imperial check: 5 ft 9 in is 69 inches. 70 kg is about 154.3 lb. 703 × 154.3 / 69² ≈ 703 × 154.3 / 4761 ≈ 22.79–22.86 depending on rounding of pounds. Small discrepancies come from rounding 70 kg to a whole pound, not from a different definition of BMI. This page converts to SI first so the default metric case is exact.

Category edges are inclusive on the lower side of each WHO sentence as commonly taught: 24.9 is still normal, 25.0 is overweight. Obesity class I begins at 30.0, class II at 35.0, class III at 40.0. Underweight is everything below 18.5, with thinness grades at 17.0, 16.0, and 16.0 downward. A BMI of 18.49 is mild thinness; 18.50 is normal. Those tenth-place cliffs are administrative, not a sudden change in physiology.

The World Health Organization adult table is a public-health instrument. It was never designed to certify “healthy” for an individual. Cross-sectional studies still show higher average rates of hypertension, dyslipidemia, and type 2 diabetes as BMI climbs through overweight and obesity classes in many populations. That is a group pattern. Your labs can disagree with your band.

Several Asia–Pacific consensus statements recommend overweight action from BMI 23 and obesity from 25 for some East and South Asian groups, because diabetes and cardiovascular risk appear at lower BMI than in many European cohorts. This calculator does not auto-apply those cutoffs. If you are using a clinic that does, map 23 and 25 yourself rather than assuming the WHO 25/30 lines are universal biology.

High lean mass inflates BMI. Rugby forwards, American football linemen, and heavyweight weightlifters routinely sit above 25 or 30 with body-fat percentages that a DEXA scan would not call obese. Low lean mass deflates the story the other way: an older adult with BMI 22 can have little muscle and a large waist. Waist circumference (often 102 cm / 40 in in men and 88 cm / 35 in in women as crude metabolic-risk flags in some guidelines) and a Navy body-fat estimate add information BMI cannot see. Even those are still estimates.

Pediatric BMI is plotted on growth charts. A 10-year-old with BMI 22 may be high on a percentile curve while an adult with BMI 22 is typical. Applying the adult WHO table to a child is a category error. This tool will still do the arithmetic if you type a short height, but the category labels remain adult WHO labels and are the wrong clinical language for pediatrics.

During pregnancy, weight includes fetus, placenta, amniotic fluid, expanded blood volume, and uterine tissue. Gestational weight-gain recommendations start from pre-pregnancy BMI, not from a BMI computed at 30 weeks. Do not use this calculator to “check if the pregnancy is overweight.”

Limb loss, edema, plaster casts, and ascites all distort weight independently of adipose tissue. Adjusted BMI formulas exist in rehabilitation literature; they are not implemented here. Extremely short or tall adults also sit farther from the populations Quetelet studied. Use clinical judgment, not a web form, when the body is not a textbook cylinder.

“Ideal weight” formulas (Devine, Robinson, Miller, Hamwi) were built for drug dosing and insurance tables, not for a personal aesthetic target. They disagree with each other by several kilograms. Compare them on the ideal weight calculator. The healthy-weight range on this BMI page is simpler: it is whatever mass keeps BMI in 18.5–24.9 at your height, which is a band, not a single destiny weight.

Energy needs are a different question. BMI does not tell you how many calories to eat. Basal metabolism depends on sex, age, height, weight, and optionally lean mass. Estimate BMR with the BMR calculator and daily expenditure with the calorie calculator, then split macros on the macro calculator. Those are still planning estimates.

Body-surface area used in some chemotherapy and physiology contexts is also not BMI. Mosteller BSA is √(height_cm × weight_kg / 3600). For 175 cm and 70 kg that is √(3.4028) ≈ 1.84 m², which you can compute on the body surface area calculator. Do not confuse m² of skin with kg/m² of Quetelet.

Adolphe Quetelet proposed the ratio of weight to height squared in the 1830s as a way to describe the “average man,” not to diagnose obesity. Ancel Keys and colleagues later popularized the name body mass index in the 1970s because, in their samples, kg/m² correlated with densitometry better than several rival indices. Public-health agencies then needed a cheap field metric. BMI won because a tape and a scale beat a hydrostatic tank.

Search traffic still clusters on “what is a healthy BMI,” “BMI 27,” and “how to calculate BMI.” The honest answer to the first is: on the WHO adult table, 18.5–24.9 is the normal band, and even that band is a compromise, not a moral grade. BMI 27 is overweight on that table. How to calculate it is kg/m² or 703×lb/in². Anything beyond that - fat loss, muscle gain, medication, surgery - is clinical work this page will not perform.

Stigma is a documented harm of BMI-only conversations. Weight-cycling, crash diets, and using a calculator as self-punishment are not what this tool is for. If food or weight thoughts are taking over your life, contact a clinician or a local eating-disorder resource. BMI cannot diagnose anorexia nervosa, bulimia, or binge-eating disorder. We deliberately did not build a tool named after those conditions.

Worked extras: 160 cm and 55 kg → 55 / 1.6² = 21.48 (normal). 180 cm and 95 kg → 95 / 1.8² = 29.32 (overweight). 165 cm and 90 kg → 90 / 1.65² ≈ 33.06 (obesity class I). 190 cm and 75 kg → 75 / 1.9² ≈ 20.78 (normal). 150 cm and 42 kg → 42 / 1.5² = 18.67 (still normal, just above 18.5). 150 cm and 41 kg → 18.22 (mild thinness). Those examples show how a few kilograms move a short adult across a cutoff that would barely register on a taller frame.

After you have BMI, composition and training tools answer different jobs: lean body mass, Army circumference body fat, target heart rate, and calories burned. Use the calculator that matches the question. This one only divides mass by height squared.