BMI Calculator (Body Mass Index)
Body mass index (BMI) is a screening number that relates your weight to your height to estimate whether an adult falls within a healthy weight range.
- Based on standard published formulas
- Instant, easy-to-read estimates
- Private: nothing leaves your device
BMI Calculator (Body Mass Index)
Enter your numbers and press Calculate
The BMI formula, step by step
This calculator uses the standard WHO formula:
BMI = weight (kg) / height² (m²)
Since you enter your height in centimeters, the first step is converting it to meters by dividing by 100.
Worked example. A 6-foot adult (183 cm) weighing 203 pounds (92 kg):
1. Height in meters: 183 / 100 = 1.83 m 2. Height squared: 1.83 × 1.83 = 3.3489 m² 3. BMI: 92 / 3.3489 = 27.5
A BMI of 27.5 falls in the overweight category (25.0–29.9).
Healthy weight range. The calculator also runs the formula in reverse to show which weights would put you in the normal range for your height:
- Minimum healthy weight = 18.5 × height² = 18.5 × 3.3489 = 62.0 kg (about 137 lb)
- Maximum healthy weight = 24.9 × height² = 24.9 × 3.3489 = 83.4 kg (about 184 lb)
So a 6-foot adult stays in the normal BMI range between roughly 137 and 184 pounds. If you prefer to work entirely in imperial units, the equivalent formula is BMI = 703 × weight (lb) / height² (in²) — for our example, 703 × 203 / 72² = 27.5, the same result.
How to use this BMI calculator
1. Enter your weight in kilograms. If you only know pounds, divide by 2.2046 — for example, 180 lb ÷ 2.2046 = 81.6 kg. Decimals are fine. 2. Enter your height in centimeters. If you know it in feet and inches, convert to total inches and multiply by 2.54 — for example, 5'10" is 70 inches × 2.54 = 178 cm. 3. Read the three results. Your BMI to one decimal place, plus the minimum and maximum weight that would put you in the normal range (18.5–24.9) for your height.
To interpret your score, check the WHO category table in the context section below. One practical tip: a single reading matters less than the trend. Weighing yourself under similar conditions — same time of day, similar clothing — and recalculating monthly tells you far more than day-to-day numbers, which can swing a couple of pounds on water weight alone.
BMI examples across real-world profiles
The table below shows BMI for four typical profiles, calculated with the WHO formula:
| Profile | Weight | Height | BMI | WHO category |
|---|---|---|---|---|
| Woman, 29 | 59 kg (130 lb) | 170 cm (5'7") | 20.4 | Normal weight |
| Woman, 51 | 62 kg (137 lb) | 160 cm (5'3") | 24.2 | Normal weight |
| Man, 38 | 92 kg (203 lb) | 183 cm (6'0") | 27.5 | Overweight |
| Man, 45 | 110 kg (243 lb) | 178 cm (5'10") | 34.7 | Obesity |
Two takeaways worth noticing:
- The 38-year-old at 203 lb sits about 19 lb above his healthy maximum of 83.4 kg (184 lb). A modest, sustained change is enough to move categories.
- For the 45-year-old, the healthy range at 178 cm runs from 58.6 to 78.9 kg (129 to 174 lb). Losing one pound a week — a commonly cited sustainable pace — would take him a bit over a year to reach the top of that range.
WHO categories and what BMI can't tell you
The WHO classifies adult BMI into four main categories:
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Obesity is further divided into class 1 (30–34.9), class 2 (35–39.9) and class 3 (40 and above).
In the United States, CDC surveys show that roughly four in ten adults have obesity, which is why BMI screening is a routine part of checkups and why clinicians track it over time.
Known limitations of BMI:
- It cannot tell muscle from fat. A 220-pound linebacker and a sedentary person of the same height and weight get identical scores.
- It says nothing about where fat is stored, yet abdominal fat carries the strongest cardiovascular risk — which is why clinicians pair BMI with waist circumference.
- It applies differently, or not at all, to children and teens (who use age- and sex-specific percentiles), pregnant women, and adults over 65.
This calculator is for educational purposes only — it is not medical advice and does not replace an evaluation by a healthcare professional.
Frequently asked questions
Is BMI accurate if I have a lot of muscle mass?
Not entirely. Muscle is denser than fat, so a strength athlete can score as overweight while carrying very little body fat — many professional football players have a BMI over 30. If you train regularly, pair BMI with waist circumference or a body composition measurement (a bioimpedance scale or skinfold calipers) before drawing conclusions.
Does this calculator work for children or during pregnancy?
No. For children and teens, BMI is interpreted with age- and sex-specific percentiles using pediatric growth charts, because body composition changes throughout development. During pregnancy, weight gain is expected and is assessed with specific guidelines at prenatal visits. In both cases, a pediatrician or OB-GYN is the right reference, not an adult BMI calculator.
What should I do if my BMI is outside the healthy range?
Don't panic — BMI is only a first screening step. If your number comes out high or low, confirm the trend over a few weeks and discuss it with your primary care provider, who will look at other factors (waist size, blood work, history). Avoid crash diets: sustainable changes to eating and activity, on the order of one pound per week, are the ones that actually stick.
Does the healthy BMI range change with age?
The official WHO thresholds (18.5 to 24.9) are the same for all adults. That said, in adults over 65, several studies find that slightly higher values are not linked to greater risk, and preserving muscle mass becomes the priority. At that stage, BMI is best read alongside strength, mobility and overall nutritional status.
About this calculator
It is the measure used by the CDC and the World Health Organization as a first-line check of weight status. This calculator returns your BMI instantly and also shows the minimum and maximum weight that would keep you inside the healthy range (18.5 to 24.9) for your height. For example, someone who is 6 feet tall (1.83 m) has a healthy range of roughly 62.0 to 83.4 kg — about 137 to 184 pounds. Keep in mind that BMI is a screening tool, not a diagnosis: it cannot tell muscle from fat, so a 200-pound athlete and a sedentary person of the same height and weight get the same score. Use it together with other markers such as waist circumference.