BMI Calculator
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Results
BMI 23.6 (healthy weight) for 160 lb at 5 ft 9 in. Healthy weight range for this height: 126–168 lb.
- Your BMI
- 23.6
- Underweight
- Below 18.5
- Healthy weight (your category)
- 18.5 to 24.9
- Overweight
- 25 to 29.9
- Obesity class 1
- 30 to 34.9
- Obesity class 2
- 35 to 39.9
- Obesity class 3
- 40 or more
BMI is a screening measure, not a diagnosis. It does not separate muscle from fat or show where fat is carried, so two people with the same BMI can have very different health. Adult categories are from the WHO and CDC and apply from age 20.
This is an estimate from a published formula, not medical advice. Talk to a doctor or registered dietitian about your own situation.
How to use the BMI calculator
- Enter your age. From 20 the adult categories apply; from 2 to 19, add the months since the last birthday and choose girl or boy.
- Pick US / Imperial (feet, inches and pounds) or Metric (centimeters and kilograms) at the top, then enter height and weight.
- Read your BMI, its category and the healthy weight range for your height. The bar chart shows where your BMI sits against each category boundary.
BMI formula
BMI = 703.07 × weight (lb) ÷ height (in)²
BMI Prime = BMI ÷ 25
Body mass index divides weight by the square of height, so taller people are allowed proportionally more weight. The US-unit version uses the factor 703.07 (often rounded to 703) to convert pounds and inches into kilograms and meters. BMI Prime, proposed by James Gadzik in 2006, divides your BMI by 25, the upper limit of the healthy range: a value under 1.0 means you are under the overweight threshold, and 1.2 means you are 20% above it.
Worked example
Someone 5 ft 9 in tall (69 inches, 175.3 cm) who weighs 160 lb (72.6 kg) has a BMI of 703.07 × 160 ÷ 69² = 23.6, which is in the healthy weight range. Their BMI Prime is 0.95, and the healthy range for their height, BMI 18.5 to 24.9, is 126–168 lb. In metric, 72 kg at 175 cm gives 72 ÷ 1.75² = 23.5.
Adult BMI categories
These categories, used by the World Health Organization and the CDC, apply to adults aged 20 and over regardless of sex. The weight columns show what each range means at 5 ft 9 in and at 170 cm.
| Category | BMI | BMI Prime | At 5 ft 9 in | At 170 cm |
|---|---|---|---|---|
| Underweight | Below 18.5 | Under 0.74 | Under 125 lb | Under 53.5 kg |
| Healthy weight | 18.5 to 24.9 | 0.74 to under 1.00 | 125 to under 169 lb | 53.5 to under 72.3 kg |
| Overweight | 25 to 29.9 | 1.00 to under 1.20 | 169 to under 203 lb | 72.3 to under 86.7 kg |
| Obesity class 1 | 30 to 34.9 | 1.20 to under 1.40 | 203 to under 237 lb | 86.7 to under 101.1 kg |
| Obesity class 2 | 35 to 39.9 | 1.40 to under 1.60 | 237 to under 271 lb | 101.1 to under 115.6 kg |
| Obesity class 3 | 40 or more | 1.60 or more | 271 lb or more | 115.6 kg or more |
NICE in the UK recommends lower thresholds for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background, whose health risks tend to rise at a lower BMI: overweight from 23 and obesity from 27.5.
BMI for children and teens
Children's BMI changes a lot as they grow, so a single adult scale would be misleading. Instead, a child's BMI is compared with children of the same age and sex. This calculator uses the LMS tables published with the CDC 2000 growth charts, month by month from age 2 to 19. Below the 5th percentile is underweight, the 5th to under the 85th is a healthy weight, the 85th to under the 95th is overweight, and the 95th or above is obesity. A BMI of 18 is the 67th percentile for a 10-year-old girl (healthy weight) but the 94th for a 4-year-old girl (overweight).
| Age | Boys 5th | Boys 85th | Boys 95th | Girls 5th | Girls 85th | Girls 95th |
|---|---|---|---|---|---|---|
| 4 years | 14.0 | 16.9 | 17.8 | 13.7 | 16.8 | 18.0 |
| 6 years | 13.7 | 17.0 | 18.4 | 13.4 | 17.1 | 18.8 |
| 8 years | 13.8 | 18.0 | 20.1 | 13.5 | 18.3 | 20.7 |
| 10 years | 14.2 | 19.4 | 22.2 | 14.0 | 20.0 | 23.0 |
| 12 years | 15.0 | 21.0 | 24.2 | 14.8 | 21.7 | 25.3 |
| 14 years | 16.0 | 22.7 | 26.0 | 15.8 | 23.3 | 27.3 |
| 16 years | 17.1 | 24.2 | 27.6 | 16.8 | 24.7 | 28.9 |
| 18 years | 18.2 | 25.7 | 29.0 | 17.6 | 25.7 | 30.3 |
The 2000 charts stop at the 97th percentile. For higher BMIs, CDC uses its 2022 extended charts, so above the 97th this calculator reports the BMI as a percentage of the 95th percentile instead; 120% or more counts as severe obesity. For a full child assessment, use the CDC Child and Teen BMI Calculator or ask the child's doctor, who will look at the growth pattern over time.
What BMI can and can't tell you
- It is a screening measure. BMI flags a possible weight-related risk quickly and cheaply, but it does not diagnose anything.
- Muscle counts as weight. Athletes and people who do a lot of strength training can have a high BMI with little body fat.
- Where fat sits matters. Fat around the waist carries more risk. Check your waist-to-height ratio in the overweight calculator or estimate body fat with the body fat calculator.
- Some groups need other measures. BMI is not used in pregnancy, and it can understate body fat in older adults who have lost muscle.
To see how your weight compares with the healthy range at different heights, use the healthy weight calculator. This is not medical advice; talk to a doctor or registered dietitian.
Sources
- CDC, Adult BMI Categories and BMI Categories for Children and Teens.
- World Health Organization, Obesity: preventing and managing the global epidemic, Technical Report Series 894 (2000).
- Kuczmarski RJ et al., 2000 CDC Growth Charts for the United States: methods and development, Vital Health Stat 11(246), 2002; LMS data file bmiagerev.csv.
- NICE guideline NG246, Overweight and obesity management (2025, updated 2026).
- Gadzik J, "How much should I weigh?" Quetelet's equation, upper weight limits, and BMI prime, Conn Med 2006;70(2):81–88.
Frequently asked questions
How do I calculate my BMI?
Divide your weight in kilograms by your height in meters squared. In US units, multiply your weight in pounds by 703 and divide by your height in inches squared. For example, 160 lb at 5 ft 9 in (69 in) gives 703 × 160 ÷ 69² = a BMI of 23.6.
What is a healthy BMI for adults?
For adults aged 20 and over, the WHO and CDC call a BMI of 18.5 to 24.9 a healthy weight. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or more is obesity, split into class 1 (30 to 34.9), class 2 (35 to 39.9) and class 3 (40 or more).
What weight is healthy for my height?
Multiply your height in meters squared by 18.5 and by 24.9. At 5 ft 9 in that gives about 126 to 168 lb, and at 175 cm about 56.7 to 76.2 kg. The calculator shows the range for any height.
How is BMI different for children and teens?
For ages 2 to 19, BMI is compared with children of the same age and sex on the CDC growth charts and given as a percentile. A BMI of 18 is about the 67th percentile for a 10-year-old girl, which is a healthy weight; the same BMI would be overweight for a 4-year-old.
Is BMI accurate?
BMI is a quick screening measure, not a diagnosis. It cannot tell muscle from fat or show where fat is stored, so very muscular people can have a high BMI and some people with a healthy BMI carry extra weight around the waist. Waist measurements and a check-up with a doctor add the missing context.