Body Mass Index (BMI) is one of the most widely used screening tools for assessing whether a person’s weight is in a healthy range relative to their height. Our free BMI Calculator gives you your BMI score and the corresponding weight category in seconds — no sign-up required. Enter your height in centimeters and your weight in kilograms, and the result appears instantly.
BMI is a useful starting point for understanding weight-related health risk, but it is not a diagnostic tool. It does not account for muscle mass, bone density, age, or fat distribution. Always discuss your results with a qualified healthcare professional for personalized guidance.
How BMI Is Calculated
The BMI formula divides your weight in kilograms by the square of your height in meters. The result is a single number that places you in one of four standard weight categories defined by the World Health Organization (WHO).
BMI = Weight (kg) ÷ Height (m)²
To use the formula, first convert your height from centimeters to meters by dividing by 100. Then square that number and divide your weight by it. For example, a person who is 175 cm tall (1.75 m) and weighs 72 kg: BMI = 72 ÷ (1.75 × 1.75) = 72 ÷ 3.0625 = 23.5 — which falls in the Normal weight range.
BMI Categories (WHO Standard)
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk of nutrient deficiencies and bone loss |
| 18.5 – 24.9 | Normal weight | Lowest risk for most weight-related conditions |
| 25.0 – 29.9 | Overweight | Moderate risk of cardiovascular and metabolic issues |
| 30.0 – 34.9 | Obese (Class I) | High risk of type 2 diabetes and heart disease |
| 35.0 – 39.9 | Obese (Class II) | Very high risk |
| 40.0 and above | Severely Obese (Class III) | Extremely high risk |
Worked Examples
Example 1: Height = 160 cm (1.60 m), Weight = 55 kg. BMI = 55 ÷ (1.60²) = 55 ÷ 2.56 = 21.5 — Normal weight.
Example 2: Height = 180 cm (1.80 m), Weight = 95 kg. BMI = 95 ÷ (1.80²) = 95 ÷ 3.24 = 29.3 — Overweight.
Example 3: Height = 165 cm (1.65 m), Weight = 50 kg. BMI = 50 ÷ (1.65²) = 50 ÷ 2.7225 = 18.4 — Underweight.
Limitations of BMI
BMI is a population-level screening tool and has well-documented limitations at the individual level. Athletes and people with high muscle mass may have elevated BMI scores despite low body fat, while older adults may have normal BMI with high fat percentage due to muscle loss over time. Similarly, BMI does not distinguish between visceral fat (around the organs, higher health risk) and subcutaneous fat (under the skin).
For a more complete picture of body composition and health risk, healthcare providers often use BMI alongside waist circumference measurements, body fat percentage testing, and blood work. BMI should be interpreted as one data point in a broader health assessment, not as a definitive verdict.
Frequently Asked Questions
What is a healthy BMI for adults?
According to the World Health Organization, a BMI between 18.5 and 24.9 is considered the normal or healthy weight range for most adults. Values below 18.5 indicate underweight, 25–29.9 indicate overweight, and 30 or above indicate obesity.
Is BMI accurate for everyone?
BMI is a useful population-level indicator but has limitations for individuals. It overestimates health risk in muscular people and may underestimate it in sedentary individuals with low muscle mass. It also does not account for age, sex, ethnicity, or where body fat is distributed.
How do I calculate BMI in imperial units (pounds and inches)?
Use the formula: BMI = (Weight in pounds × 703) ÷ (Height in inches)². For example, a person who is 5 ft 10 in (70 inches) and weighs 175 lbs: BMI = (175 × 703) ÷ (70²) = 123,025 ÷ 4,900 = 25.1.
What BMI is considered obese?
A BMI of 30 or higher is classified as obese. The WHO further divides obesity into Class I (30–34.9), Class II (35–39.9), and Class III or “severe obesity” (40 and above). Each class carries progressively higher risks for conditions like type 2 diabetes, cardiovascular disease, and sleep apnea.
Can children use this BMI calculator?
This calculator uses the adult BMI formula, which is not appropriate for children and teenagers. For individuals under 18, BMI is interpreted differently using age- and sex-specific growth charts (BMI-for-age percentiles). Consult a pediatrician for an accurate assessment.
What should I do if my BMI is outside the normal range?
A BMI outside the normal range is a signal to speak with a healthcare professional, not a diagnosis. Your doctor can assess your overall health picture — including blood pressure, cholesterol, blood sugar, and lifestyle factors — and recommend personalized steps if needed.