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BMI Calculator

Body Mass Index (BMI) divides weight in kilograms by height in metres squared to produce a single screening number for weight status.

Underweight (<18.5)Normal (18.5–25)Overweight (25–30)Obese (30+)

BMI Classification Chart (WHO)

The World Health Organization sets adult BMI cut-off points at 18.5, 25, 30, 35 and 40 kg/m². These ranges apply to both men and women aged 20 and above.

ClassificationBMI Range (kg/m²)
Severe ThinnessBelow 16
Moderate Thinness16 to 17
Mild Thinness17 to 18.5
Normal18.5 to 25
Overweight25 to 30
Obese Class I30 to 35
Obese Class II35 to 40
Obese Class IIIAbove 40

How BMI Is Calculated

BMI uses two formulas depending on the unit system. Both produce the same result for a given height and weight.

Unit SystemFormula
MetricBMI = weight (kg) ÷ height² (m)
ImperialBMI = 703 × weight (lb) ÷ height² (in)

BMI Chart by Height and Weight

Find your height and weight in the grid below. Each cell shows the resulting BMI, colour coded by category.

Height \ Weight40kg50kg60kg70kg80kg90kg100kg110kg120kg
150cm182227313640444953
160cm162023273135394347
170cm141721242831353842
180cm121519222528313437
190cm111417192225283033
200cm101315182023252830
UnderweightNormalOverweightObese IObese IIObese III

Health Risks Linked to BMI Ranges

Health organisations such as the CDC and WHO associate both high and low BMI ranges with specific risks. BMI is a screening indicator here, not a diagnosis.

Risks linked to a high BMI

  • High blood pressure and elevated LDL cholesterol
  • Type 2 diabetes
  • Coronary heart disease and stroke
  • Osteoarthritis and joint strain
  • Sleep apnea and breathing difficulty

Risks linked to a low BMI

  • Nutrient deficiencies and anemia
  • Reduced bone density over time
  • Lowered immune function
  • Growth concerns in children and teens
  • Higher surgical and recovery complications

Limitations of BMI

BMI measures excess weight, not excess body fat, so it does not separate muscle mass from fat mass. A muscular or highly active individual can register a high BMI while carrying low body fat, and an inactive individual can register a normal BMI while carrying high body fat. BMI is generally reliable for 90 to 95% of adults but is less accurate for athletes, older adults, and pregnant women.

Why Your Weight Reading Needs to Be Accurate

A BMI calculation is only as good as the number you put into it. A half kilogram error barely shifts the result, but for someone following a nutritionist's weekly targets, recovering weight after an illness, or working toward a doctor set goal, that same half kilogram is the difference between "on track" and "off track."

Some people weigh in daily as part of a structured diet plan. Others are trying to gain weight back after being underweight, or keeping an eye on a health condition where sudden changes matter. A few just want one honest number they can trust week to week, without wondering if the scale itself is the problem.

Whatever the reason, the accuracy has to come from the scale before it can come from the math.

How BMI Is Used in Real Situations

Supervised weight loss

Someone on a nutritionist directed plan tracks weekly weight against a target BMI range, adjusting the diet as the number moves.

Supervised weight gain

A person advised to gain weight after being underweight tracks progress toward the lower edge of the normal BMI range, month over month.

Strength training and muscle mass

A gym goer with high muscle mass often lands in "overweight" on BMI alone, so they pair it with a body fat percentage reading for the full picture.

Postpartum recovery

New mothers track weight changes over several months as part of postpartum recovery, alongside guidance from their doctor.

Pre-surgery and routine screening

Many hospitals and insurers record BMI as a standard screening figure a doctor reviews alongside blood pressure and other vitals.

Child growth tracking

Pediatricians plot a child's BMI percentile over years, not as a single reading, to spot a growth trend that needs attention.

Frequently Asked Questions

What is a healthy BMI range?

A healthy BMI for adults falls between 18.5 kg/m² and 25 kg/m², based on World Health Organization classification.

Is BMI accurate for athletes or muscular people?

BMI can overestimate body fat in muscular individuals because the formula does not distinguish muscle mass from fat mass.

Does BMI work the same way for children?

No. The CDC uses age and gender specific BMI percentiles for children aged 2 to 20, not the fixed adult cut-offs.

What should I do if my BMI is outside the normal range?

Track your weight on an accurate scale over time and consult a doctor before making significant lifestyle changes.

How often should I check my BMI?

Checking weight weekly and recalculating BMI monthly gives a stable trend without over-focusing on daily fluctuations.

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