BodyIndex

BMI Calculator

Quick body-mass index check — with the WHO healthy range shown alongside your result.

Height (cm)

Weight (kg)

Body Mass Index

24.6

Healthy weight

WHO categories (adults)

Underweight — below 18.5
Healthy weight — 18.5 to 24.9
Overweight — 25.0 to 29.9
Obese — 30.0 and above

What you entered

Height: 178 cmWeight: 78 kg

1
Convert height to metres
h = 178 cm ÷ 100= 1.78 m
2
Square the height
h² = 1.78²= 3.1684 m²
3
Divide weight by height²
BMI = 78 kg ÷ 3.1684 m²= 24.6
4
Compare to WHO ranges
Underweight <18.5 · Healthy 18.5–24.9 · Overweight 25–29.9 · Obese 30+= Healthy weight

Result

BMI: 24.6 (Healthy weight)

A BMI of 24.6 falls in the "Healthy weight" range. BMI is a quick screening tool — it doesn't account for muscle mass, bone density, or body composition, so treat it as one signal, not a diagnosis.

BMI for common height and weight combinations

BMI is weight in kilograms divided by height in metres squared. The WHO cut-offs are under 18.5 underweight, 18.5-24.9 healthy, 25-29.9 overweight, and 30 or above obese.

Weight	Height	BMI	Category
50 kg	170 cm	17.3	Underweight
60 kg	170 cm	20.8	Healthy weight
70 kg	170 cm	24.2	Healthy weight
80 kg	170 cm	27.7	Overweight
90 kg	170 cm	31.1	Obese
100 kg	170 cm	34.6	Obese
70 kg	160 cm	27.3	Overweight
70 kg	180 cm	21.6	Healthy weight

BMI does not distinguish muscle from fat and is not reliable for athletes, pregnant people, or children. General wellness information only, not medical advice. Discuss any health decision with a qualified clinician.

What BMI does and doesn't tell you

BMI is a population-level screening tool, not a diagnosis. It can misclassify very muscular athletes as overweight and slender people with low muscle mass as healthy. Use it as one signal, not the only one.

How BMI is calculated

BMI = weight (kg) ÷ height² (m²). For imperial: BMI = weight (lb) × 703 ÷ height² (in²). Example: 70 kg and 1.75 m → 70 ÷ 3.0625 = 22.9 BMI. The same formula applies to all adults regardless of age or sex.

WHO BMI categories

Underweight: below 18.5. Normal weight: 18.5–24.9. Overweight: 25.0–29.9. Obesity Class I: 30.0–34.9. Obesity Class II: 35.0–39.9. Obesity Class III: 40.0+. These ranges are designed for adults 20+ years old. For children and teens, BMI is interpreted using age-and-sex-specific percentile charts.

BMI limitations and alternatives

BMI doesn't distinguish between muscle mass, bone density, and fat. A bodybuilder with 8% body fat could have a 'overweight' BMI of 28. Better body composition metrics include waist-to-hip ratio, body fat percentage (DEXA scan or US Navy method), and waist circumference. The WHO considers waist >102 cm (men) or >88 cm (women) as high risk regardless of BMI.

Frequently asked questions

What is a healthy BMI?

The WHO defines a healthy (normal) BMI as 18.5–24.9 for adults. Within this range, you have the lowest statistical risk of weight-related health conditions like type 2 diabetes, heart disease, and hypertension.

How do I calculate BMI manually?

Divide your weight in kilograms by your height in meters squared. For example: 75 kg ÷ (1.80 m)² = 75 ÷ 3.24 = 23.1 BMI. In imperial: multiply weight in pounds by 703, then divide by height in inches squared (165 lb × 703 ÷ 67² = 25.8).

Is BMI accurate for athletes?

BMI can be misleading for muscular athletes. Muscle weighs more than fat per unit volume, so a lean, muscular person may have a 'overweight' BMI despite low body fat. For athletes, body fat percentage (via DEXA scan or skinfold calipers) is a more accurate measure.

Does BMI change with age?

The BMI formula stays the same for all adults, but body composition shifts with age — adults tend to lose muscle and gain fat. A BMI of 25 at age 25 reflects different body composition than a BMI of 25 at age 65. Some researchers suggest slightly higher 'healthy' ranges (23–28) for older adults.