BMI Calculator
Calculate your Body Mass Index from your height and weight, see your category, and find the healthy weight range for your height.
BMI is a quick screen, not a diagnosis. It doesn't distinguish muscle from fat, so very muscular people may read high. Not medical advice.
How to use this calculator
Enter your height in feet and inches and your weight in pounds, then click Calculate. The tool returns your BMI value, the standard adult category it falls into, and the weight range that corresponds to a normal BMI for your exact height. All three numbers appear instantly — no sign-up required.
What BMI measures — and what it doesn't
Body Mass Index is a ratio of weight to height squared. It was introduced in the 19th century as a population statistics tool and later adopted by public health agencies as a quick screening method for weight-related health risk. The CDC uses BMI to categorize adults into four groups: underweight, normal weight, overweight, and obese.
BMI is useful precisely because it takes only two measurements and has decades of research linking it to disease risk at the population level. That said, it is a screening tool, not a diagnostic test. It does not distinguish between fat mass and lean mass, so a person who is very muscular may have a high BMI while carrying little body fat. Conversely, someone with low muscle mass and high body fat can have a normal BMI yet still carry elevated health risk. Where you store fat — particularly around the abdomen — also matters and is not captured by BMI.
BMI categories at a glance
- Under 18.5 — Underweight
- 18.5 – 24.9 — Normal weight
- 25.0 – 29.9 — Overweight
- 30.0 and above — Obese
These cutoffs apply to adults aged 20 and older regardless of sex. For children and teens, the CDC uses age- and sex-specific growth charts instead of fixed cutoffs because body composition changes considerably through adolescence.
Worked example — step by step
Take someone who is 5 feet 10 inches tall (70 inches) and weighs 185 lb.
- Convert height to inches: 5 × 12 + 10 = 70 in
- Square the height: 70 × 70 = 4,900 in²
- Multiply weight by 703: 185 × 703 = 130,055
- Divide: 130,055 ÷ 4,900 = BMI 26.5 — overweight range
For the same person to reach the top of the normal range (BMI 24.9), they would need to weigh approximately 173 lb — a difference of about 12 lb. The calculator shows this healthy weight range automatically.
How to interpret your result
A BMI in the normal range does not guarantee good health, and a BMI slightly above normal does not mean you are unhealthy. BMI is best used as a starting conversation with your healthcare provider. If your result falls in the overweight or obese range, pairing it with a waist circumference measurement gives a clearer picture of abdominal fat risk. Men with a waist over 40 inches and women over 35 inches face elevated risk for heart disease and type 2 diabetes, regardless of BMI.
Common mistakes to avoid
- Treating BMI as a diagnosis. A high BMI warrants follow-up, not a conclusion. Only a clinician can diagnose obesity or assess overall metabolic health.
- Ignoring where fat is stored. Visceral fat — the kind stored around the organs — is more metabolically harmful than fat stored under the skin. Waist measurements capture this; BMI does not.
- Comparing across very different body types. Highly trained athletes, older adults with muscle loss, and pregnant women are groups where BMI is especially unreliable.
- Using adult categories for children. BMI means something different under age 20 — use age- and sex-specific percentile charts for anyone under 20.
- Focusing only on reaching a number. Sustainable lifestyle habits — diet quality, physical activity, sleep, and stress — matter more for long-term health than hitting a specific BMI.
The formula
BMI (US units) = 703 × weight(lb) ÷ height(in)²
BMI (metric) = weight(kg) ÷ height(m)²
BMI is a screening tool, not a medical diagnosis. Consult a healthcare professional for personalized guidance.
How we calculate this
BMI is calculated as 703 × weight(lb) ÷ height(in)², and categorized using the standard CDC adult ranges. BMI is a screening tool, not a diagnosis, and doesn't distinguish muscle from fat.
Sources
Frequently asked questions
How is BMI calculated?
BMI is weight divided by height squared. In US customary units the formula is 703 × weight(lb) ÷ height(in)². For example, a person weighing 170 lb at 70 inches tall has a BMI of 703 × 170 ÷ 4,900 ≈ 24.4, which falls in the normal range.
What is a healthy BMI for adults?
The CDC defines four standard categories for adults 20 and older: under 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 or above is obese. The calculator also shows the specific weight range that falls in the normal band for your height.
Is BMI an accurate measure of health?
BMI is a useful population-level screening tool but has real limitations as an individual measure. It cannot distinguish muscle from fat, so muscular athletes often read as overweight, while someone with low muscle mass and high body fat can read as normal. Use it as one data point alongside other measures.
Does BMI apply to children and teenagers?
For people under 20, BMI is still calculated the same way but interpreted using age- and sex-specific growth charts rather than fixed adult cutoffs. The CDC provides separate BMI-for-age percentile tools for children and teens.
What is a better measure of body fat or health risk?
Waist circumference, waist-to-height ratio, or a body fat percentage estimate give more insight into where fat is stored and the associated health risks. Our body fat calculator uses the U.S. Navy tape method to estimate body fat from simple measurements.
How much weight do I need to lose to reach a normal BMI?
The calculator shows the healthy weight range for your height, so you can subtract your current weight from the top of that range to get the minimum loss needed. Keep in mind that sustainable fat loss is typically 0.5–1 pound per week.
Does BMI differ by ethnicity?
Research suggests the health risks associated with higher BMI can vary across ethnic groups. Some organizations recommend lower BMI thresholds for people of Asian descent, where risks for type 2 diabetes and cardiovascular disease may appear at lower BMIs. Discuss individual risk with a healthcare provider.