BMI
calculator.
Find your body mass index from height and weight, the CDC weight category it falls in and the weight range that corresponds to a healthy BMI at your height. For ages 2 to 19 it gives the CDC BMI-for-age percentile, calculated from CDC’s own growth-chart tables.
A BMI of 24.4 at 5 ft 9 in is in the CDC adult category “Healthy weight”. The healthy-weight range for this height (BMI 18.5 to 24.9) is 125.3 lb to 168.6 lb.
- BMI
- 24.4 kg/m²
- CDC adult category
- Healthy weight
- Healthy-weight range for this height
- 125.3 lb to 168.6 lb
- Same range in kg
- 56.8 kg to 76.5 kg
- Your weight is
- inside the healthy-weight range
- BMI Prime (BMI ÷ 25)
- 0.97
BMI = 165 lb ÷ (69 in)² × 703.0696 = 24.366 kg/m² → 24.4; healthy range = 18.5 × 1.7526² to 24.9 × 1.7526² = 56.8 to 76.5 kgWeight over height squared,
read the CDC way.
- BMI = weight (kg) ÷ height (m)². In US units, BMI = weight (lb) ÷ height (in)² × 703; the exact factor is 703.0696, from 1 lb = 0.45359237 kg and 1 in = 0.0254 m, and that is what the calculator uses.
- Adults (20 and older): CDC categories are underweight below 18.5, healthy weight 18.5 to under 25, overweight 25 to under 30, and obesity at 30 or more (class 1 under 35, class 2 under 40, class 3 at 40 or more). The category is read from BMI rounded to one decimal, the precision of the published cutoffs.
- Healthy-weight range for a height = 18.5 × height² to 24.9 × height², the NHLBI healthy BMI range. BMI Prime = BMI ÷ 25, so 1.00 is the upper limit of a healthy BMI.
- Ages 2 to 19: BMI is compared with CDC 2000 growth-chart data for the child’s sex and age in completed months. z = ((BMI ÷ M)^L − 1) ÷ (L × S) and the percentile is the normal probability of z. Above the 95th percentile CDC’s 2022 extended method is used: percentile = 90 + 10 × Φ((BMI − P95) ÷ sigma).
- Child categories: under the 5th percentile underweight, 5th to under 85th healthy weight, 85th to under 95th overweight, 95th or above obesity; severe obesity at 120% of the 95th percentile or BMI 35 or more. The percentile is shown truncated to one decimal, so a value just under a cutoff never displays as the cutoff.
How do you calculate BMI?
Divide weight in kilograms by height in meters squared. In pounds and inches, divide by height in inches squared and multiply by 703. Someone 5 ft 9 in (69 inches) tall who weighs 165 lb has a BMI of 165 ÷ 69² × 703.07 = 165 ÷ 4,761 × 703.07 = 24.4. In metric, 175 cm and 75 kg give 75 ÷ 1.75² = 75 ÷ 3.0625 = 24.5. The unit is kg/m², but BMI is normally written as a plain number.
BMI = kg ÷ m²
BMI = lb ÷ in² × 703What is a healthy weight for my height?
For adults, a healthy BMI is 18.5 to 24.9, so the matching weights are 18.5 and 24.9 times your height in meters squared. At 5 ft 9 in (1.7526 m, 3.0716 m²) that is 18.5 × 3.0716 = 56.8 kg to 24.9 × 3.0716 = 76.5 kg, or 125.3 to 168.6 lb. The range is wide on purpose: BMI cannot tell muscle from fat, so many weights in it can be healthy for the same height. The ideal weight calculator shows the same range next to the older single-number formulas.
lowest = 18.5 × height²
highest = 24.9 × height²What are the BMI categories for adults?
CDC uses the same cutoffs for adult men and women of every age: underweight below 18.5, healthy weight 18.5 to under 25, overweight 25 to under 30, and obesity 30 or more. Obesity is split into class 1 (30 to under 35), class 2 (35 to under 40) and class 3, also called severe obesity (40 or more). CDC’s own example is an adult 5 ft 8 in tall who weighs 200 lb: 200 ÷ 68² × 703 = 30.4, class 1 obesity. CDC describes BMI as a screening measure, to be considered with other factors, not a diagnosis.
How is BMI calculated for children and teens?
The BMI number is worked out the same way, but for ages 2 to 19 it is compared with children of the same sex and age, because body fat changes as children grow. CDC publishes three numbers, L, M and S, for each month of age, and the percentile follows from z = ((BMI ÷ M)^L − 1) ÷ (L × S). A 10-year-old boy who is 140 cm tall and weighs 32 kg has a BMI of 16.3. At 10 years 0 months CDC lists L = −2.7656, M = 16.646 and S = 0.12011, which gives z = −0.166 and the 43.4th percentile, a healthy weight. CDC’s own example is a 12-year-old girl, 5 ft tall and 136 lb: BMI 26.6, at the 96th percentile, which is in the obesity category; the calculator gives 96.0.
z = ((BMI ÷ M)^L − 1) ÷ (L × S)
percentile = Φ(z) × 100How are BMI percentiles above the 95th calculated?
The 2000 charts stop being reliable at very high BMI, so in 2022 CDC published an extended method for values above the 95th percentile: percentile = 90 + 10 × Φ((BMI − P95) ÷ sigma), where P95 is the 95th-percentile BMI for the age and sigma is a dispersion value CDC lists for each month. CDC’s worked example is a boy aged 4 years 2 months with a BMI of 22.6. P95 is 17.8219 and sigma is 2.3983, so the percentile is 90 + 10 × Φ(1.9923) = 99.77 and the z-score is 2.83. His BMI is 127% of the 95th percentile. CDC counts 120% of the 95th percentile or more (or a BMI of 35 or more) as severe obesity, and the calculator shows that percentage for every child.
percentile = 90 + 10 × Φ((BMI − P95) ÷ sigma)What is BMI Prime?
BMI Prime, proposed by Gadzik (Connecticut Medicine, 2006), divides BMI by 25, the upper limit of a healthy BMI. A BMI of 24.4 is a BMI Prime of 24.4 ÷ 25 = 0.97, just under the limit; CDC’s 30.4 example is 1.22, or 22% above it. Because it is a plain ratio, a BMI Prime of 1.22 also means the weight is 22% above the heaviest weight with a healthy BMI at that height. It applies to adults only.
Worked examples.
Adult in US units
5 ft 9 in, 165 lb.
BMI 24.4, healthy weight; the healthy-weight range at this height is 125.3 lb to 168.6 lb.
Load this exampleCDC’s adult example
5 ft 8 in, 200 lb.
BMI 30.4, obesity (class 1); 36.2 lb above the top of the healthy-weight range.
Load this exampleAdult in metric
175 cm, 75 kg.
BMI 24.5, healthy weight; the range is 56.7 kg to 76.3 kg.
Load this example10-year-old boy
140 cm, 32 kg, 10 years 0 months.
43.4th percentile, healthy weight.
Load this exampleCDC’s 12-year-old girl
5 ft 0 in, 136 lb, 12 years 0 months.
96.0th percentile, obesity; BMI 26.6.
Load this exampleAbove the 95th percentile
CDC’s extended-method example: a boy aged 4 years 2 months, 100 cm, 22.6 kg (BMI 22.6).
99.7th percentile (99.77), z-score 2.83, 126.8% of the 95th percentile.
Load this exampleWhat this calculator
does not do.
- BMI is a screening measure, not a diagnosis. It does not measure body fat directly, cannot tell fat from muscle and bone, and does not show where fat is carried. Very muscular people can have a high BMI without excess fat.
- Adult categories are not designed for pregnancy, and they are the same for every adult age, sex and ethnicity, although body fat at a given BMI differs between groups. Some countries use lower cutoffs for people of Asian descent; this calculator uses the CDC categories only.
- Child percentiles use age in completed months, as CDC’s tables do. CDC’s own tools work from exact dates, so a child near a month boundary may differ slightly. The calculator does not track growth over time, which is how clinicians read growth charts.
- This is general information, not medical advice. Ask a doctor or other clinician what your result, or your child’s, means for health.
Common questions.
What is a normal BMI?
For adults, CDC calls 18.5 to under 25 a healthy weight. Below 18.5 is underweight, 25 to under 30 overweight and 30 or more obesity.
Is BMI different for men and women?
Not for adults: the formula and the cutoffs are the same. For children and teens the percentile depends on sex and age, so a boy and a girl with the same BMI can be at different percentiles.
What is the BMI formula in pounds and inches?
BMI = weight in pounds ÷ (height in inches)² × 703. For 150 lb at 5 ft 6 in (66 in): 150 ÷ 4,356 × 703 = 24.2.
Why does my child’s BMI have a percentile?
Children’s body fat changes with age and differs between boys and girls, so CDC compares a child’s BMI with a reference group of the same age and sex. The 85th percentile means the BMI is higher than that of 85% of the reference children.
What is a BMI z-score?
The number of standard deviations from the median BMI for the age and sex. A z-score of 0 is the 50th percentile, about 1.04 is the 85th, and about 1.64 is the 95th.
Should I use this calculator for weight-loss or medical decisions?
No. It gives general information from public CDC formulas. Decisions about weight, diet or treatment belong with a clinician who knows your health.
- CDC: Adult BMI Categories — adult categories from underweight to class 3 obesity; BMI is a screening measure
- CDC: BMI Frequently Asked Questions — metric and US formulas (× 703); 5 ft 8 in, 200 lb example (30.4); limitations
- CDC: Child and Teen BMI Categories — percentile categories for ages 2 through 19, severe obesity at 120% of the 95th percentile; 12-year-old girl example
- CDC: Percentile Data Files with LMS Values — BMI-for-age L, M, S by sex and month (bmiagerev.csv); z-score formula; half-month age convention
- CDC: Extended BMI-for-Age Growth Charts data files — 2022 sigma values and the percentile formula above the 95th; 4-year-old boy worked example
- NHLBI (NIH): Calculate Your Body Mass Index — healthy BMI range 18.5–24.9; BMI does not account for muscle mass or body composition
Adult BMI is weight ÷ height² with exact unit factors, classified on BMI rounded to one decimal. For ages 2 to 19 the module embeds CDC’s L, M, S and sigma values for every month from 2 years 0 months to 19 years 11 months, copied unchanged from CDC’s bmi-age-2022.csv (L, M and S match the 2000 file bmiagerev.csv exactly). Percentiles use a double-precision normal distribution. Tests reproduce CDC’s three published examples, check seven ages against CDC’s own 5th to 99.9th percentile and z-score columns, recompute five cases separately in Python from the CDC file, and check continuity at the 95th percentile, monotonicity and US/metric agreement over 600 random cases.
Built and reviewed by CalculatorLab against the sources above; every worked example on this page is re-checked by our automated test suite before each release. How we build and check calculators. Found a problem? Tell us.