How to check your BMI
Choose metric or U.S. units and enter a recent weight and your standing height without shoes. In U.S. mode, height goes in as total inches, so 5 feet 9 inches is 69, not 5.9. Switching units converts what you've already typed.
Waist size is optional. It adds a separate waist-to-height ratio and doesn't change your BMI or category.
- Pick Metric (kg and cm) or U.S. customary (lb and total inches).
- Enter your weight and height.
- Add your waist measurement if you want the waist-to-height ratio.
- Calculate and read your BMI, CDC category and the boundary weights for your height.
BMI formula
Body mass index is weight divided by height squared. The result is always in kg/m2, even if you enter pounds and inches. The calculator keeps the full unrounded number to pick your category and only rounds what it shows you.
It also shows two extra indices. BMI Prime is your BMI divided by 25, so 1.00 sits exactly at the start of the overweight range. The ponderal index divides weight by height cubed instead of squared.
BMI = weight (kg) / height (m)^2BMI = 703 x weight (lb) / height (in)^2Weight at a BMI boundary = boundary BMI x height (m)^2BMI Prime = BMI / 25Waist-to-height ratio = waist / height, in the same units
Adult BMI categories
CDC uses the same categories for all adults age 20 and older. WHO uses the same cut points for overweight (25 and above) and obesity (30 and above). The boundaries are exact: a BMI of 24.96 shows as 25.0 when rounded, but it's still under 25, so the calculator keeps it in the healthy weight range.
| Category | BMI range | Exact rule |
|---|---|---|
| Underweight | Below 18.5 | BMI < 18.5 |
| Healthy weight | 18.5 to under 25 | 18.5 <= BMI < 25 |
| Overweight | 25 to under 30 | 25 <= BMI < 30 |
| Class 1 obesity | 30 to under 35 | 30 <= BMI < 35 |
| Class 2 obesity | 35 to under 40 | 35 <= BMI < 40 |
| Class 3 obesity | 40 or higher | BMI >= 40 |
BMI chart by height
These are the weights where each main category begins at common heights, worked out from the formula. At 5 feet 8 inches, for example, the healthy weight range runs from about 121.7 lb up to just under 164.4 lb. The calculator gives you the same numbers for your exact height.
| Height | BMI 18.5 | BMI 25 | BMI 30 |
|---|---|---|---|
| 5 ft 0 in (60 in) | 94.7 lb | 128.0 lb | 153.6 lb |
| 5 ft 2 in (62 in) | 101.1 lb | 136.7 lb | 164.0 lb |
| 5 ft 4 in (64 in) | 107.8 lb | 145.6 lb | 174.8 lb |
| 5 ft 6 in (66 in) | 114.6 lb | 154.9 lb | 185.9 lb |
| 5 ft 8 in (68 in) | 121.7 lb | 164.4 lb | 197.3 lb |
| 5 ft 10 in (70 in) | 128.9 lb | 174.2 lb | 209.1 lb |
| 6 ft 0 in (72 in) | 136.4 lb | 184.3 lb | 221.2 lb |
| 6 ft 2 in (74 in) | 144.1 lb | 194.7 lb | 233.7 lb |
| 175 cm | 56.7 kg | 76.6 kg | 91.9 kg |
Worked example in metric and pounds
Take an adult who weighs 70 kg and is 175 cm tall. Height squared is 1.75 x 1.75 = 3.0625. 70 divided by 3.0625 is 22.857, shown as 22.9. That's in the healthy weight range, which at this height runs from about 56.7 kg to just under 76.6 kg. With an 85 cm waist, the waist-to-height ratio is 85 / 175 = 0.486.
Now someone who weighs 180 lb at 5 feet 9 inches (69 inches). 703 x 180 / 69 squared gives about 26.6, in the overweight range. BMI Prime for the first person is 22.857 / 25, about 0.91.
BMI calculator for men and women
Adult BMI uses one formula and one set of categories for men and women. CDC applies the same table regardless of sex, age or race, which is why the calculator doesn't ask for either.
Sex does matter for children and teens. CDC reads BMI for ages 2 through 19 as a percentile on sex- and age-specific growth charts, so the adult categories here don't apply to anyone under 20. They also don't apply during pregnancy.
What BMI can't tell you
BMI is a screening number, not a diagnosis. CDC notes it can't tell fat from muscle and bone, and it doesn't show where fat sits. A muscular adult can land in the overweight range, and an older adult with low muscle mass can look healthy on BMI alone.
Some guidelines use lower cut points for some groups. NICE in the UK uses 23 for overweight and 27.5 for obesity in adults of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background. NICE also suggests a waist-to-height ratio for adults with a BMI under 35: 0.4 to 0.49 is healthy, 0.5 to 0.59 is increased and 0.6 or more is high.
Treat this result as an estimate. Talk to a doctor or other clinician before acting on it, especially for unexplained weight change, pregnancy, eating disorder concerns, medication changes or a child's growth.
Sources
These public health sources back up the formula, categories, limits and waist-to-height ranges on this page.