BMI Calculator — Body Mass Index Free

Height (cm)

Weight (kg)

Age (optional)

Gender (optional)

BMI Categories (WHO Standard)

BMI Range	Category	Health Risk
Below 18.5	Underweight	Moderate risk
18.5 – 24.9	Normal weight	Low risk (Good)
25.0 – 29.9	Overweight	Increased risk
30.0 – 34.9	Obese Class I	High risk
35.0 – 39.9	Obese Class II	Very high risk
40.0 and above	Obese Class III	Extremely high risk

BMI is a screening tool, not a diagnostic measure. Consult a healthcare professional for medical advice.

BMI Formula

Metric: weight(kg) ÷ height²(m)
Imperial: 703 × weight(lb) ÷ height²(in)
Normal: 18.5 – 24.9
Created by Adolphe Quetelet
Used by WHO worldwide

BMI Limitations

Doesn't measure body fat
Athletes may score high
Varies by age & ethnicity
Use with other metrics

Related Tools

Free BMI Calculator

Calculate your Body Mass Index instantly using metric (kg/cm) or imperial (lb/in) measurements. See your BMI category, ideal healthy weight range, personalised health tips and a visual BMI gauge. Supports all WHO standard BMI categories from underweight to obese class III.

Features

BMI Calculation

Accurate BMI using WHO formula: weight(kg) ÷ height²(m).

Visual BMI Meter

Animated needle gauge shows your position across all BMI categories at a glance.

Ideal Weight Range

Shows your healthy weight range (BMI 18.5–24.9) at your exact height.

Health Tips

Personalised actionable health advice based on your specific BMI category.

Metric & Imperial

Switch seamlessly between kg/cm and lb/ft/in units.

Completely Private

No personal data is stored or transmitted. All calculations are local.

Who Uses This Tool?

Health-Conscious IndividualsMonitor weight status and track progress toward health goals.

Fitness EnthusiastsUse alongside body fat measurements for a fuller picture of body composition.

Healthcare ProfessionalsQuick BMI reference for patient consultations and health screenings.

StudentsLearn the WHO BMI classification system for health and biology courses.

Common Questions

Is BMI an accurate measure of health?

BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat, so athletes often appear "overweight". It also doesn't account for age, sex, ethnicity or bone density.

What BMI is considered healthy?

The WHO defines 18.5–24.9 as "Normal Weight" and the healthy range. Below 18.5 is underweight, 25–29.9 is overweight, and 30+ is obese.

Can BMI be wrong for muscular people?

Yes — muscle is denser and heavier than fat. Many athletes and bodybuilders have a BMI in the "overweight" or even "obese" range despite having very low body fat percentages.

Are BMI ranges different for different ethnicities?

Yes — the WHO and some health organisations recommend lower thresholds for South Asian, East Asian and some other populations, where health risks associated with excess body fat appear at lower BMI values.

Pro Tip

BMI should be considered alongside other measurements like waist circumference (a strong predictor of cardiovascular risk), body fat percentage, blood pressure and blood glucose for a complete picture of health. A BMI of 22–23 is generally associated with the lowest mortality risk.

Did You Know?

1832

BMI Formula Created

The BMI formula was created by Belgian mathematician Adolphe Quetelet in 1832 as a statistical tool to study populations — not to assess individual health. It was called the "Quetelet Index" for over 150 years.

1972

BMI Named by Dr. Keys

American physiologist Ancel Keys coined the term "Body Mass Index" in 1972 after evaluating several body fat measures. He explicitly noted it was unsuitable for individual clinical assessment.

40%

BMI Misclassification Rate

Studies show BMI misclassifies the metabolic health of approximately 40% of people. Many muscular athletes are classified "obese" while some metabolically unhealthy thin people appear "normal."

BMI Health Ranges (WHO)

BMI Range	Category	Health Risk	Action
Below 16.0	Severely underweight	Very high	Immediate medical attention
16.0 – 18.4	Underweight	Moderate	Consult nutritionist
18.5 – 24.9	Normal weight	Lowest risk	Maintain lifestyle
25.0 – 27.4	Slightly overweight	Low–moderate	Monitor, mild changes
27.5 – 29.9	Overweight	Moderate	Diet and exercise
30.0 – 34.9	Obese Class I	High	Medical guidance
35.0 – 39.9	Obese Class II	Very high	Medical intervention
40.0+	Obese Class III	Extremely high	Immediate care

You May Also Ask

Why is BMI different for children?

Children's BMI uses age- and sex-specific percentiles rather than fixed cutoffs, because body fat changes significantly during growth. A child's BMI is compared to others of the same age and sex. Cutoffs like "overweight" and "obese" correspond to the 85th and 95th percentiles respectively.

What is the Body Adiposity Index (BAI) and is it better than BMI?

BAI uses hip circumference and height to estimate body fat percentage, potentially more accurately than BMI for some populations. However, research has not consistently shown BAI to outperform BMI, and it requires additional measurements. The most accurate consumer body fat measures are DEXA scans and hydrostatic weighing.

What BMI is associated with the lowest mortality risk?

Multiple large studies find the lowest all-cause mortality associated with BMI 22–23 for younger adults. Interestingly, research consistently finds slightly overweight individuals (BMI 25–27.5) have similar or lower mortality than those at the low end of "normal" — a finding called the "obesity paradox."

Common Mistakes

Using BMI as the sole health indicator

BMI ignores muscle mass, bone density, fat distribution and metabolic health. A bodybuilder and a sedentary person can have identical BMIs.

Combine BMI with waist circumference, blood pressure, cholesterol and glucose.

Applying adult BMI ranges to athletes

Elite athletes often have BMI 27–30 (technically "overweight") with body fat under 10%. BMI is not validated for athletic populations.

Use body fat percentage measurement for athletes — DEXA or skinfold calipers.

Ignoring waist circumference

Where fat is stored matters more than how much. Abdominal fat (waist >88cm women, >102cm men) significantly increases cardiovascular risk regardless of BMI.

Measure waist circumference alongside BMI for a more complete picture.