Calculate your BMI from your height and weight, check your adult BMI category, and see the weight range corresponding to a BMI of 18.5–24.9.
Body mass index (BMI) is a calculated measure of weight relative to height. For adults, it is commonly used as a screening measure to classify weight status into underweight, healthy weight, overweight, or obesity. BMI is useful for population-level and initial screening, but it is not a direct measurement of body fat or a diagnosis of health.
In metric units, BMI is calculated by dividing body weight in kilograms by height in meters squared.
BMI = weight (kg) ÷ height² (m²)
When using pounds and inches, the conversion factor is included in the formula:
BMI = 703 × weight (lb) ÷ height² (in²)
For example, someone who is 5 ft 10 in tall and weighs 175 lb has a BMI of about 25.1. The calculator above performs the same calculation automatically and handles the unit conversion for you.
The commonly used adult BMI categories are:
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25.0–29.9 | Overweight |
| 30.0 or higher | Obesity |
These categories are reference ranges for adults. BMI should be considered with other information when assessing an individual's health rather than treated as a diagnosis on its own.
For adults, the commonly used healthy-weight BMI range is 18.5 to 24.9. Height matters because the same BMI corresponds to different body weights at different heights. Your age does not change the standard adult BMI calculation, but BMI is interpreted differently for children and teenagers because their body composition changes during growth.
This calculator is intended for adult use. Children and teens need age- and sex-specific BMI-for-age interpretation rather than the adult categories shown here.
If you want to know what body weight corresponds to a particular BMI, the calculation can be reversed. For a given height, the calculator finds the weights corresponding to BMI 18.5 and BMI 24.9 and displays that as a reference range.
This can help answer searches such as “ideal weight for height,” but BMI alone cannot determine an individual's ideal or healthiest body weight. Muscle mass, fat distribution, medical history, waist size, and other factors can matter too.
If your goal is weight loss, you can use the Calorie Deficit Calculator to estimate a calorie target and projected timeline, then use real-world changes in body weight and performance to adjust your plan.
BMI is especially important to interpret carefully if you lift weights or carry substantial muscle mass. The calculation only uses height and weight, so it cannot tell whether that weight comes from muscle, fat, bone, or other lean tissue.
A muscular athlete can therefore have a BMI in the overweight or obesity range without having the same body-fat level as someone with less lean mass. That does not make the BMI calculation mathematically wrong; it means BMI may provide less information about body composition for that individual.
If body composition is your main question, use our Body Fat Calculator as another reference rather than relying on BMI alone.
Muscle mass can make BMI less informative because muscle contributes to body weight. BMI cannot distinguish fat mass from lean mass, so a highly muscular person may receive an overweight or obesity classification from BMI even when their body-fat level is relatively low.
For gym-goers, it is therefore useful to view BMI as one measurement in a broader picture. Waist circumference, body-fat estimates, training performance, health history, and other relevant measures can provide additional context.
The standard adult BMI calculation is the same for men and women, and the commonly used adult category cutoffs are the same. BMI can still relate differently to body composition between individuals, so sex alone should not be used to turn a BMI number into a complete assessment of health.
BMI answers a narrow question about weight relative to height. RepMaths has other calculators that can answer the next question in a fitness or nutrition workflow:
RepMaths uses the standard adult BMI calculation and the commonly used adult BMI categories of below 18.5, 18.5–24.9, 25.0–29.9, and 30.0 or higher. The BMI formula and category ranges are consistent with guidance published by the U.S. Centers for Disease Control and Prevention (CDC) and National Heart, Lung, and Blood Institute (NHLBI). The limitations wording reflects CDC and NIDDK guidance that BMI is a screening measure and does not directly distinguish fat mass from lean mass.
BMI-based weight ranges shown by this calculator are mathematical conversions of the 18.5–24.9 reference range for the entered height. They are not personalized medical recommendations.
For adults, a BMI from 18.5 to 24.9 is commonly classified as healthy weight. Your height determines which body-weight values correspond to that BMI range. Children and teens need age- and sex-specific BMI interpretation.
BMI is a screening measure based on height and weight. It does not directly measure body fat and cannot distinguish fat mass from lean mass such as muscle and bone.
High muscularity can make BMI less informative because muscle contributes to body weight. A muscular person can have a high BMI without having the same body-fat level as someone with less lean mass.
BMI is weight in kilograms divided by height in meters squared. With pounds and inches, BMI equals 703 times weight in pounds divided by height in inches squared.
The standard adult BMI calculation and commonly used adult category cutoffs are the same for men and women. BMI should still be interpreted with other relevant health information.
For adults, the commonly used healthy BMI reference range is 18.5 to 24.9. A BMI calculator can convert that range into a height-specific weight range, but it should be treated as a reference rather than a personalized ideal-weight prescription.