BMI Calculator - Body Mass Index

Key facts

BMI = weight (kg) ÷ height (m)² — the world’s most used weight-for-height check (imperial: 703 × lb ÷ in²).
Healthy range is 18.5 to 24.9; 25–29.9 is overweight, 30+ is obesity (WHO categories).
Used by doctors and insurers worldwide as a screening tool — not a diagnosis.
BMI cannot tell muscle from fat — muscular athletes may score "overweight" while lean.

Body Mass Index (BMI) is the world’s most widely used quick check of whether your weight is in a healthy range for your height. This free BMI calculator computes your BMI instantly from your weight and height and tells you which category you fall into.

Enter your weight in kilograms, enter your height, and pick your unit — centimetres, inches, or metres. Press Calculate to get your BMI instantly: a plain-English verdict, a colour gauge showing where you land, and your healthy weight range for your height.

How to use

Enter your weight in kilograms.
Enter your height and choose your unit: centimetres, inches, or metres.
Press Calculate. Your BMI, category, verdict sentence, colour gauge, and healthy weight range appear.
Compare against the category table below to see where you stand.

Quick answer: Body Mass Index estimates body fat from height and weight: BMI equals weight in kilograms divided by height in meters squared. The World Health Organization classes 18.5 to 24.9 as the healthy adult range, 25 to 29.9 as overweight, and 30 or more as obesity. BMI is a screening tool, not a diagnosis.

Last reviewed: September 2026

BMI formula

BMI = weight (kg) ÷ [height (m)]²

Term	Meaning
weight	Your body weight in kilograms.
height	Your height in metres (divide centimetres by 100).

Example: 70 kg at 175 cm → 70 ÷ 1.75² = 70 ÷ 3.0625 = 22.9 — comfortably in the healthy range.

Worked examples

Healthy range

70 kg, 175 cm: BMI = 70 ÷ (1.75 × 1.75) = 22.9 — Normal range (18.5–24.9).

Overweight range

85 kg, 170 cm: BMI = 85 ÷ (1.70 × 1.70) = 29.4 — Overweight (25–29.9), close to the obesity threshold of 30.

For this height, the healthy weight range is roughly 53.5–72.0 kg (18.5 × 1.7² to 24.9 × 1.7²).

Imperial units example

150 lb, 5'6" (66 in): BMI = 703 x 150 / (66 x 66) = 703 x 150 / 4356 = 24.2 — Normal range (18.5-24.9).

WHO BMI categories

BMI	Category	What it means
Below 18.5	Underweight	May indicate undernourishment; consider medical advice.
18.5 – 24.9	Normal / healthy	Associated with the lowest health risks.
25 – 29.9	Overweight	Above the healthy range; lifestyle review sensible.
30 and above	Obesity	Higher risk of heart disease, diabetes and more; see a doctor.

For children and teens, BMI is interpreted against age-and-sex growth charts, not these adult cut-offs.

Healthy weight range by height

The calculator shows your range automatically; this table gives the WHO healthy band (BMI 18.5-24.9) at common heights.

Height	Healthy weight
160 cm (5'3")	47.4-63.7 kg
170 cm (5'7")	53.5-72.0 kg
175 cm (5'9")	56.7-76.3 kg
180 cm (5'11")	59.9-80.7 kg
185 cm (6'1")	63.3-85.2 kg

Frequently asked questions

Is BMI accurate?

It is a useful population-level screening tool, but it cannot tell muscle from fat. Very muscular people, pregnant women and the elderly should interpret it with a clinician.

How do I calculate BMI with pounds and inches?

BMI = 703 × weight (lb) ÷ height (in)². Or use the calculator above: it takes weight in kg with height in centimetres, inches, or metres.

What is a healthy BMI?

18.5 to 24.9 for adults, according to the World Health Organization.

Does BMI work for children?

Not with adult cut-offs. Children’s BMI is plotted on percentile charts for their age and sex — ask a paediatrician.

My BMI is 27 — should I worry?

It is above the healthy range, which statistically raises some health risks. Small, sustained changes to diet and activity move it more than crash diets do.

Why does the calculator say “screening, not diagnosis”?

Because health is more than one number: waist size, blood pressure, cholesterol, fitness and family history all matter alongside BMI.

How much protein should I eat to lower my BMI?

While losing weight, aim for about 1.2 to 2.0 grams of protein per kilogram of body weight per day. Extra protein preserves lean muscle during a calorie deficit, which keeps your metabolism from slowing as your BMI falls. Spread it across meals, roughly 25 to 40 grams per meal, and pair it with resistance training for the best body-composition result.

Is BMI accurate for athletes?

Not always. BMI only uses height and weight, so muscular athletes can score as overweight despite low body fat. It also misses fat distribution. For athletes, body fat percentage, waist measurements, or performance-based assessments give a truer picture than BMI alone.

What is a good BMI for my age?

For adults aged 20 and over, the healthy BMI range is 18.5 to 24.9, the same for men and women of any age, according to the CDC and WHO. BMI cut-offs do not change with age for adults; for children and teens, BMI is interpreted against age-and-sex percentile charts instead. Note that some health bodies suggest slightly different action points for Asian populations, and very muscular adults may read high despite low body fat.

What are the BMI obesity classes?

Obesity (BMI 30 and above) is divided into three classes: Class I is 30.0-34.9, Class II is 35.0-39.9, and Class III (severe obesity) is 40 and above. The classes help clinicians assess health risk — higher classes are linked to greater risk of heart disease, diabetes, and high blood pressure — but a clinician looks at blood pressure, cholesterol, and waist size too, not BMI alone.

Sources

World Health Organization — BMI classifications and healthy ranges
CDC — About adult BMI and how to interpret it

Key takeaways

BMI = kg ÷ m²; 18.5–24.9 is the adult healthy range.
It screens populations well but can misread very muscular or elderly bodies.
Use it as a starting point for a conversation with a clinician, not a verdict.

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