BMI Calculator
Body mass index (BMI) is a quick screening number that compares your weight with your height. Enter your details below in US or metric units. The math runs in your browser and nothing you type is sent or stored.
Not medical advice. This calculator gives an educational estimate only. It does not diagnose any condition or replace advice from a doctor, registered dietitian or other licensed professional. If you are pregnant, under 18, managing a medical condition or taking medication, talk to a clinician before changing how you eat or train.
How the BMI calculator works
BMI divides your body weight by the square of your height. The metric formula is
BMI = weight (kg) ÷ height (m)². With US units you multiply by a conversion
factor: BMI = 703 × weight (lb) ÷ height (in)². For example, a person who is
5 ft 9 in (69 inches) and weighs 170 lb has a BMI of 703 × 170 ÷ 69² ≈ 25.1. The
calculator also flips the formula around to show the weight range that matches a BMI of 18.5 to 24.9 at
your height, which is often more useful than the single number.
How to read your result
For adults aged 20 and older, the CDC and NIH use these categories:
| BMI | 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 |
| 40.0 and above | Obesity class 3 (severe) |
Treat the category as a prompt, not a verdict. A BMI just past a cutoff, such as 25.3, means about the same thing for your health as 24.8. What matters more is the direction you are moving over months and how BMI lines up with other markers like waist size, blood pressure, blood sugar and cholesterol.
Limitations of BMI
- It can't tell muscle from fat. Muscular people can land in the "overweight" range with little body fat, and older adults who have lost muscle can look "healthy" while carrying extra fat.
- It ignores where fat sits. Fat around the abdomen is linked to more metabolic risk. The NIH suggests also measuring waist circumference; above 40 inches (102 cm) for men or 35 inches (88 cm) for non-pregnant women raises risk.
- Cutoffs vary by population. Research shows that many people of Asian descent face higher risk of type 2 diabetes at lower BMIs, and some guidelines use lower thresholds for them.
- It's not for children or pregnancy. People aged 2 to 19 are assessed with BMI-for-age percentiles on CDC growth charts, and BMI doesn't apply during pregnancy.
For a longer look at these blind spots, read What BMI Can't Tell You.
What to do next
If your BMI is outside the healthy range, the next step is a conversation with a healthcare provider, who can look at your full picture. If you decide to change your weight, the TDEE calculator estimates how many calories you burn each day, and the macro calculator splits a calorie target into protein, fat and carbs.
Sources
- Centers for Disease Control and Prevention. Adult BMI Categories.
- National Heart, Lung, and Blood Institute (NIH). Calculate Your Body Mass Index and waist circumference guidance.
- Centers for Disease Control and Prevention. Child and Teen BMI Categories.
- WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet. 2004;363(9403):157-163.
- Okorodudu DO, et al. Diagnostic performance of body mass index to identify obesity as defined by body adiposity: a systematic review and meta-analysis. International Journal of Obesity. 2010;34(5):791-799.