“Obesity” covers a wide range of body sizes. A BMI of 31 and a BMI of 48 are both obesity, but the health risks and the treatment options are very different. That is why health agencies split adult obesity into three classes. The US Centers for Disease Control and Prevention (CDC) and NICE in England use the same cut-offs.
How to use the calculator
- Choose metric (cm and kg) or US units (feet, inches and pounds).
- Enter a height and weight measured without shoes and in light clothing — home scales and a wall measure are fine.
- Read the BMI, the adult category and, at a BMI of 30 or more, the obesity class.
- Check the weight chart below to see where the class boundaries fall for your height.
The calculator is for adults aged 20 and over. Children and teens are compared with growth charts for their age and sex instead.
The three classes
- Obesity class 1: BMI 30 to under 35.
- Obesity class 2: BMI 35 to under 40.
- Obesity class 3 (severe): BMI 40 or more.
BMI is weight in kilograms divided by height in metres squared. The calculator rounds it to one decimal place, as CDC does, and then finds the band it falls in, so the number shown always sits inside the class shown.
“Class 1 Obesity: 30 to less than 35 … Class 2 Obesity: 35 to less than 40 … Class 3 Obesity (Severe Obesity): 40 or greater”
“Classify the degree of overweight or obesity in adults as follows, if they are not in the groups covered by recommendation 1.9.11: healthy weight: BMI 18.5 kg/m2 to 24.9 kg/m2; overweight: BMI 25 kg/m2 to 29.9 kg/m2; obesity class 1: BMI 30 kg/m2 to 34.9 kg/m2; obesity class 2: BMI 35 kg/m2 to 39.9 kg/m2; obesity class 3: BMI 40 kg/m2 or more.”
CDC also calls class 3 severe obesity.
A worked example
A person 175 cm tall who weighs 100 kg has a BMI of 100 ÷ (1.75 × 1.75) = 32.7. That is obesity class 1 (BMI 30 to under 35). At that height, the obesity range starts at about 91.9 kg, so this person is about 8.1 kg above it.
Where each class starts, by height
| Height | Class 1 from (BMI 30) | Class 2 from (BMI 35) | Class 3 from (BMI 40) |
|---|---|---|---|
| 150 cm (4 ft 11 in) | 67.5 kg / 149 lb | 78.8 kg / 174 lb | 90.0 kg / 198 lb |
| 155 cm (5 ft 1 in) | 72.1 kg / 159 lb | 84.1 kg / 185 lb | 96.1 kg / 212 lb |
| 160 cm (5 ft 3 in) | 76.8 kg / 169 lb | 89.6 kg / 198 lb | 102.4 kg / 226 lb |
| 165 cm (5 ft 5 in) | 81.7 kg / 180 lb | 95.3 kg / 210 lb | 108.9 kg / 240 lb |
| 170 cm (5 ft 7 in) | 86.7 kg / 191 lb | 101.1 kg / 223 lb | 115.6 kg / 255 lb |
| 175 cm (5 ft 9 in) | 91.9 kg / 203 lb | 107.2 kg / 236 lb | 122.5 kg / 270 lb |
| 180 cm (5 ft 11 in) | 97.2 kg / 214 lb | 113.4 kg / 250 lb | 129.6 kg / 286 lb |
| 185 cm (6 ft 1 in) | 102.7 kg / 226 lb | 119.8 kg / 264 lb | 136.9 kg / 302 lb |
| 190 cm (6 ft 3 in) | 108.3 kg / 239 lb | 126.3 kg / 279 lb | 144.4 kg / 318 lb |
| 195 cm (6 ft 5 in) | 114.1 kg / 251 lb | 133.1 kg / 293 lb | 152.1 kg / 335 lb |
Weights are rounded. Someone exactly on a boundary may land on either side once the BMI is rounded to one decimal.
What the class can’t tell you
A class is a label for a BMI range, not a diagnosis. BMI cannot tell fat from muscle and bone, and it doesn’t show what type of fat someone has or where it sits in the body. Two people in the same class can have very different health. NICE adds two important cautions:
“People with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background are prone to central adiposity and their cardiometabolic risk occurs at lower BMI, so use lower BMI thresholds as a practical measure of overweight and obesity: overweight: BMI 23 kg/m2 to 27.4 kg/m2; obesity: BMI 27.5 kg/m2 or above. For people in these groups, obesity classes 2 and 3 are usually identified by reducing the thresholds highlighted in recommendation 1.9.10 by 2.5 kg/m2.”
“Interpret BMI with caution in adults with high muscle mass because it may be a less accurate measure of central adiposity in this group. … Interpret BMI with caution in people aged 65 and over, taking into account comorbidities, conditions that may affect functional capacity and the possible protective effect of having a slightly higher BMI when older.”
This calculator uses the standard cut-offs for everyone, because that is what CDC publishes. If the lower NICE thresholds apply to you, read your result against those instead. A health professional can look at the whole picture — waist size, blood pressure, blood tests and family history. Our waist-to-height ratio calculator adds one more piece.
How common is each class?
In the US, the NHANES survey sends trained staff to measure the height and weight of a national sample of people, in survey cycles that usually last two years. In Aug 2021–Aug 2023, 40.3% of adults aged 20 and over had obesity, and 9.7% had class 3 (severe) obesity. Back in 1999–2000, those figures were 30.5% and 4.7%.
US adults with obesity and with class 3 obesity
What this means: Class 3 obesity has grown faster than obesity overall: from 4.7% to 9.7% of adults.
- Obesity (class 1–3)
- Class 3
Show the numbers as a table
| Survey years | Obesity | Class 3 |
|---|---|---|
| 1999–2000 | 30.5% | 4.7% |
| 2001–2002 | 30.6% | 5.1% |
| 2003–2004 | 32.2% | 4.8% |
| 2005–2006 | 34.3% | 5.9% |
| 2007–2008 | 33.8% | 5.7% |
| 2009–2010 | 35.8% | 6.3% |
| 2011–2012 | 34.9% | 6.4% |
| 2013–2014 | 37.7% | 7.7% |
| 2015–2016 | 39.6% | 7.7% |
| 2017–March 2020 | 41.9% | 9.2% |
| Aug 2021–Aug 2023 | 40.3% | 9.7% |
Measured height and weight, adults 20 and over, age-adjusted. Class 3 = BMI 40 or more.
Source: CDC NHANES.
Worldwide, the higher classes are expected to keep growing:
385 million
adults are projected to have a BMI above 35 by 2030, up from 157 million in 2010 (World Obesity Atlas 2025 projection).
Sources
- US Centers for Disease Control and Prevention, Adult BMI Categories (published ; checked )
- National Institute for Health and Care Excellence (NICE), Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity (published ; checked )
- National Institute for Health and Care Excellence (NICE), Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity (published ; checked )
- National Institute for Health and Care Excellence (NICE), Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity (published ; checked )
- US Centers for Disease Control and Prevention, About Body Mass Index (BMI) (published ; checked )
- US Centers for Disease Control and Prevention, About Body Mass Index (BMI) (published ; checked )
- World Obesity Federation, World Obesity Atlas 2025 (published ; checked )
- National Health and Nutrition Examination Survey (NHANES), 1999–2000 to Aug 2021–Aug 2023
- NHES I (1959–62), NHES II (1963–65), NHES III (1966–70), NHANES I (1971–74), NHANES II (1976–80), HHANES (1982–84), NHANES III (1988–94)
How we process every dataset is explained on How we calculate; all sources are listed on Data sources.
Last updated
Written by the ObesitySurvey team. Not medical advice. Data last rebuilt 1 October 2026.