BMI Calculator — Check Your BMI and Obesity Class Instantly

Body Mass Index (BMI) is a simple screening calculation that relates weight to height, producing a single number used to place adults into standard weight categories — including the WHO obesity classes for anyone whose result falls into the higher ranges. This calculator returns that number instantly, along with the category it falls into, a reverse-BMI target weight range, and reference context like average weight figures and how BMI compares to other measures such as waist-to-height ratio. For daily energy estimates alongside height and weight, see the calorie calculator.

It's worth saying clearly upfront: BMI is a screening tool, not a diagnosis, and it doesn't account for muscle mass, bone density, or body composition. The categories below describe population-level screening ranges, not a judgment about any individual body — a BMI number on its own doesn't determine whether someone is healthy. Browse all calculators if you need a different tool.

How BMI Is Calculated

The BMI Formula

BMI = Weight (kg) ÷ Height (m)²

Or, using imperial units:

BMI = (Weight (lbs) ÷ Height (in)²) × 703

For example, converting 163 lbs to kg gives approximately 73.9 kg — a conversion step that's handled automatically by this calculator's unit toggle, so figures can be entered in either pounds or kilograms without manual conversion.

Understanding Obesity Classes and BMI Categories

WHO Obesity Class I, II, and III Explained

The World Health Organization's standard adult BMI categories are:

These obesity classes exist to give clinicians and researchers a consistent way to describe risk ranges at a population level. A single obesity class label doesn't capture individual health factors like fitness level, muscle mass, or where fat is distributed on the body — which is exactly why doctors use BMI alongside other measurements, not as a standalone diagnosis.

A Visual BMI Gauge (Not a 3D Model)

This calculator reports the BMI number together with the WHO category it falls into across the underweight-to-obesity-class-III range. That result is a two-dimensional numeric indicator, not a 3D body model or simulation — for anyone specifically searching for a 3D BMI visualizer or an interactive body-shape rendering, that's a different (and much more complex) type of tool than a standard BMI calculator provides.

BMI Worked Examples by Height and Weight

Seeing real height-and-weight combinations calculated out often clarifies the categories faster than the formula alone. Here are several examples across a range of heights, all calculated using the same standard formula — shown as reference data points, not as judgments about any individual's weight:

Each row follows the identical formula — only the height and weight inputs change. A calculated BMI figure and its category are factual outputs of the formula; whether a specific number represents a given individual's situation depends on factors well beyond height and weight alone, including muscle mass, age, sex, and overall health context best assessed by a healthcare provider.

Reverse BMI Calculator: Find a Target Weight Range

How Reverse BMI Works

A reverse BMI calculator flips the standard formula around: instead of entering height and weight to get a BMI, height and a target BMI range are entered to find the corresponding weight range. Rearranging the formula:

Target Weight (kg) = Target BMI × Height (m)²

For example, at a height of 5'6" (1.68m), the "normal weight" BMI range of 18.5–24.9 corresponds to a weight range of approximately 52.2 kg to 70.3 kg (about 115–155 lbs). This reverse calculation is useful for anyone who wants to see a full target range for their height rather than checking one weight value at a time. Use Reverse BMI in the calculator above to run it.

Average Weight for Women and Men — Reference Ranges

Why "Average" Weight Isn't a Target

Average weight for women (and men) varies significantly by country, age group, and height, since it reflects population data rather than a health recommendation. Public health data (such as CDC NHANES survey figures) shows the average adult weight in the US has shifted over recent decades, but "average" describes a statistical midpoint of a population — it isn't a target or a health benchmark for any individual. A weight range for a given height is better read from BMI category, waist measurements, and a healthcare provider's assessment than by comparing to a population average alone.

Army BMI Calculator vs. Standard BMI

The Army Tape Test vs. BMI

The US Army's official body composition standard is not simply a standard BMI calculation. Soldiers who exceed the Army's height-and-weight screening table are evaluated using a circumference-based body fat percentage measurement (commonly called the "tape test"), which estimates body fat using neck, waist, and (for women) hip measurements rather than relying on BMI alone. This is because BMI doesn't distinguish muscle mass from fat mass, which matters significantly in a population with above-average muscle mass from physical training.

This calculator currently provides standard civilian BMI, not the Army's specific height-weight screening table or tape-test body fat formula. Service members checking their status against official Army Body Composition Program standards should reference the current AR 600-9 regulation or their unit's official assessment rather than relying on a standard BMI result alone.

Waist-to-Height Ratio and Weight Percentile — Related but Different Measures

Waist-to-Height Ratio

Waist-to-height ratio (WHtR) is calculated differently from BMI — it divides waist circumference by height, and some research suggests it may better reflect abdominal fat distribution than BMI alone. This calculator does not currently include a dedicated waist-to-height ratio tool; it focuses specifically on the standard BMI formula.

Weight Percentile Calculators

Weight percentile calculators (comparing an individual's weight to a percentile ranking within a population, commonly used in pediatric growth charts) use a different statistical method than adult BMI categories. This calculator is built for adult BMI screening and does not currently provide pediatric growth percentile calculations.

How This Compares to the NHS BMI Calculator

The UK's National Health Service (NHS) provides its own official BMI checker using the same standard WHO-based formula and category ranges used throughout this page, with additional guidance noting that health risk at a given BMI can begin at lower thresholds for some ethnic groups (an adjustment some UK clinical guidance applies for South Asian, Chinese, and other populations). For the official NHS tool and their specific clinical guidance, visit the NHS BMI checker on nhs.uk. This calculator uses the standard international BMI formula and category thresholds described above and is not an NHS service.

Limitations of BMI and How to Measure Body Measurements Properly

BMI is a useful screening tool specifically because it's quick and requires only height and weight, but it has real limitations worth understanding:

• It doesn't distinguish muscle mass from fat mass, which can place very muscular individuals in a higher BMI category
• It doesn't account for where fat is distributed on the body, which matters for certain health-risk assessments
• Standard category thresholds were developed primarily from European population data and may not translate identically across all ethnic groups

For an accurate result, measure body weight and height carefully: weigh without heavy clothing or shoes, ideally at a consistent time of day, and measure height standing straight against a flat wall without shoes. These basic body measurement practices reduce the small input errors that most commonly throw off a BMI result.

Frequently Asked Questions