Free calculator
BMI Calculator
Written by the GymStreak coaching teamUpdated
For adults aged 20 and over. Under 20, BMI is judged with age- and sex-specific growth charts.
The short answer
BMI (body mass index) is your weight in kilograms divided by your height in metres squared. For adults, a BMI of 18.5 to 24.9 is classed as a healthy weight, 25 to 29.9 as overweight and 30 or more as obesity. For example, someone who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ 3.06 = 22.9.
01 / How it works
How the bmi calculator works
BMI compares your weight with your height. Taller people are naturally heavier, so dividing weight by height squared gives a single number that can be compared across people of different heights. The ratio was devised by the 19th-century statistician Adolphe Quetelet, which is why it is also called the Quetelet index. In 1972 the physiologist Ancel Keys and colleagues popularised it for population studies and named it the body mass index, while pointing out that it only roughly reflects body fat.
Enter your weight and height in kilograms and centimetres, or in pounds and feet and inches. Imperial inputs are converted to metric first, so both give the same answer. The calculator then shows your BMI to one decimal place, the adult category it falls into, and the range of weights that would give a BMI of 18.5 to 24.9 at your height.
The categories are the ones the World Health Organization and the US Centers for Disease Control and Prevention use for adults, and they are the same for men and women. BMI is a screening number: it tells you how your weight compares with your height, not how much of it is fat or muscle. Read the limitations below before you act on it.
02 / Formula
The BMI formulas
BMI (metric)
BMI = weight ÷ height²
- weight in kilograms
- height in metres (divide centimetres by 100)
- BMI in kg/m²
BMI (pounds and inches)
BMI = 703 × weight ÷ height²
- weight in pounds
- height in inches (feet × 12 + inches)
The 703 is just a unit conversion (0.4536 kg per lb ÷ 0.0254² m² per square inch ≈ 703), so both versions give the same BMI.
Healthy-weight range for your height
Lowest = 18.5 × height² Highest = 24.9 × height²
- height in metres; the answer is in kilograms
This is the BMI formula turned around: the weights that give a BMI of 18.5 and 24.9 at your height.
03 / Worked example
Worked examples
Metric: 70 kg and 175 cm
An adult weighs 70 kg and is 175 cm tall.
- 1Height in metres = 175 ÷ 100 = 1.75 m
- 2Height² = 1.75 × 1.75 = 3.0625
- 3BMI = 70 ÷ 3.0625 = 22.9
- 4Healthy range = 18.5 × 3.0625 to 24.9 × 3.0625
- 5Healthy range = 56.7 kg to 76.3 kg
A BMI of 22.9, in the healthy-weight range. At 175 cm, any weight from about 57 to 76 kg gives a BMI of 18.5 to 24.9.
Imperial: 200 lb and 5 ft 10 in
An adult weighs 200 lb and is 5 ft 10 in tall.
- 1Height in inches = 5 × 12 + 10 = 70 in
- 2Height² = 70 × 70 = 4,900
- 3BMI = 703 × 200 ÷ 4,900 = 140,600 ÷ 4,900 = 28.7
- 4Healthy range = 18.5 × 4,900 ÷ 703 to 24.9 × 4,900 ÷ 703
- 5Healthy range ≈ 129 lb to 174 lb
A BMI of 28.7, in the overweight range. At 5 ft 10 in, the healthy-weight range is about 129 to 174 lb. If this person lifts regularly, some of that weight may be muscle: see the limitations below.
04 / Reference
BMI charts and tables
| BMI (kg/m²) | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 to 34.9 | Obesity class 1 |
| 35.0 to 39.9 | Obesity class 2 |
| 40 or above | Obesity class 3 (severe obesity) |
For adults aged 20 and over, regardless of sex. Under 20, BMI is judged against age- and sex-specific growth charts instead.
| Height | Approx. ft/in | Healthy range (kg) | Healthy range (lb) | BMI 30 starts at |
|---|---|---|---|---|
| 150 cm | 4 ft 11 in | 41.6–56.0 kg | 92–124 lb | 67.5 kg |
| 155 cm | 5 ft 1 in | 44.4–59.8 kg | 98–132 lb | 72.1 kg |
| 160 cm | 5 ft 3 in | 47.4–63.7 kg | 104–141 lb | 76.8 kg |
| 165 cm | 5 ft 5 in | 50.4–67.8 kg | 111–149 lb | 81.7 kg |
| 170 cm | 5 ft 7 in | 53.5–72.0 kg | 118–159 lb | 86.7 kg |
| 175 cm | 5 ft 9 in | 56.7–76.3 kg | 125–168 lb | 91.9 kg |
| 180 cm | 5 ft 11 in | 59.9–80.7 kg | 132–178 lb | 97.2 kg |
| 185 cm | 6 ft 1 in | 63.3–85.2 kg | 140–188 lb | 102.7 kg |
| 190 cm | 6 ft 3 in | 66.8–89.9 kg | 147–198 lb | 108.3 kg |
| 195 cm | 6 ft 5 in | 70.3–94.7 kg | 155–209 lb | 114.1 kg |
Calculated with the formulas above. Feet and inches are rounded to the nearest inch, so use the calculator for your exact height.
| BMI (kg/m²) | What the WHO expert consultation said |
|---|---|
| 23.0 | Suggested public health action point: many Asian groups already have raised risk of type 2 diabetes and heart disease below the usual overweight cut-off of 25 |
| 27.5 | Suggested as a further public health action point |
| 32.5 | Suggested as a further public health action point |
| 37.5 | Suggested as a further public health action point |
The consultation kept the standard WHO categories for international use and left it to each country to decide how to use these extra points. Observed risk started between BMI 22 and 25 depending on the population.
05 / Training
What to do with your BMI
- Use it alongside a second measure. Waist size or a body fat estimate tells you far more about how much of your weight is fat. Try the body fat calculator, which uses a tape measure.
- If your BMI is above 25 and you want to lose fat, start with a modest calorie deficit and plenty of protein. The TDEE calculator gives you a calorie target, and how to create and stick to a calorie deficit covers the practical side.
- Lift weights whatever your number. Strength training helps you keep or build muscle while your weight changes. Big movements such as goblet squats, barbell squats, pushups and seated cable rows are a good base.
- If you lift and your BMI reads "overweight", check your waist or body fat before you decide to diet. See how to tell if you are gaining muscle without weighing yourself.
- If your BMI is under 18.5, it is worth talking to a doctor, especially if you have lost weight without trying.
06 / Limitations
Limitations and safety
BMI does not measure body fat. The CDC notes that it cannot tell fat, muscle and bone apart, so muscular people can be classed as overweight and people with little muscle can have a "healthy" BMI while carrying a lot of fat. In a meta-analysis of 32 samples, the usual obesity cut-offs missed about half of the people whose measured body fat was high.
The same BMI carries different risk in different people. The WHO expert consultation found that many Asian populations have a higher risk of type 2 diabetes and heart disease at BMIs below 25, which is why some countries use lower cut-offs.
The adult categories do not apply to children and teenagers, and BMI is not used to judge weight during pregnancy.
This calculator gives an estimate for general fitness education. It is not medical advice and does not diagnose anything. If you have a health condition, are pregnant, or are new to hard exercise, check with a doctor first.
07 / FAQ
Frequently asked questions
How do you calculate BMI?
Divide your weight in kilograms by your height in metres squared. For example, 70 kg ÷ (1.75 m × 1.75 m) = 22.9. In pounds and inches, multiply your weight in pounds by 703 and divide by your height in inches squared.
What is a healthy BMI for adults?
A BMI of 18.5 to 24.9 is classed as a healthy weight for adults aged 20 and over. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or more is obesity.
How do I calculate my BMI in pounds and feet?
Turn your height into inches (feet × 12 + inches), square it, then work out 703 × your weight in pounds ÷ that number. Someone who is 5 ft 10 in (70 in) and 200 lb has a BMI of 703 × 200 ÷ 4,900 = 28.7.
What BMI is considered obese?
A BMI of 30 or more is classed as obesity. It is split into class 1 (30 to 34.9), class 2 (35 to 39.9) and class 3, or severe obesity (40 or more).
Is BMI accurate if I have a lot of muscle?
Not very. BMI cannot tell muscle from fat, so people who lift weights and carry a lot of muscle can have a BMI of 25 or more while being lean. A waist measurement or a body fat estimate gives a better picture.
Is BMI different for men and women?
No. For adults, the same formula and the same categories are used for men and women. For children and teenagers, BMI is compared with growth charts that do depend on age and sex.
Is BMI different for Asian people?
The formula is the same, but a 2004 WHO expert consultation found that many Asian populations have raised health risks at BMIs below 25. It suggested extra action points at 23, 27.5, 32.5 and 37.5, and some countries use lower cut-offs as a result.
What weight should I be for my height?
A BMI of 18.5 to 24.9 covers a range of weights at every height. To find yours, multiply 18.5 and 24.9 by your height in metres squared: at 1.75 m that is about 57 to 76 kg. The calculator shows the range for your height in kg or lb.
Sources
- Centers for Disease Control and Prevention. Adult BMI categories. Updated 2024.
- Centers for Disease Control and Prevention. About body mass index (BMI). Updated 2025.
- World Health Organization. Obesity and overweight: fact sheet. December 2025.
- WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004;363(9403):157-163.
- Keys A, Fidanza F, Karvonen MJ, Kimura N, Taylor HL. Indices of relative weight and obesity. J Chronic Dis. 1972;25(6):329-343.
- Okorodudu DO, Jumean MF, Montori VM, et al. Diagnostic performance of body mass index to identify obesity as defined by body adiposity: a systematic review and meta-analysis. Int J Obes. 2010;34(5):791-799.
- Nuttall FQ. Body mass index: obesity, BMI, and health: a critical review. Nutr Today. 2015;50(3):117-128.
Related tools
- Body Fat CalculatorEstimate your body fat percentage with a tape measure, using the US Navy method in cm or inches.
- TDEE CalculatorEstimate the calories you burn per day, then get a target for losing, keeping or gaining weight.
- Macro CalculatorGet daily calories and grams of protein, fat and carbs for losing fat, maintaining or building muscle.
From the blog
Exercises to try
- Goblet SquatsBeginner compound kettlebell exercise for the quadriceps, also working the glutes.
- Barbell SquatsBeginner compound barbell exercise for the quadriceps, also working the glutes.
- PushupsBeginner compound bodyweight exercise for the chest, also working the triceps and shoulders.
- Seated Cable RowsIntermediate compound cable row machine exercise for the middle back, also working the forearms and biceps.
- TreadmillBeginner cardio on the treadmill, for heart and lung fitness.
Turn a number into a plan
GymStreak builds workouts around your goal, tracks your body weight, and syncs with Apple Health or Health Connect, so you can see the trend, not just one reading.
