BMI Calculator

Overview

How to use this calculator

1. Measure or look up your current body weight in kilograms. If you only have pounds, convert to kilograms first (lbs ÷ 2.20462 ≈ kg).
2. Measure your height in centimeters using a stadiometer, tape measure, or your medical records. If you only know your height in feet and inches, convert to centimeters (inches × 2.54).
3. Enter your weight (kg) and height (cm) into the calculator fields.
4. The calculator converts height to meters, squares it, divides your weight by that number, and returns your BMI rounded to a reasonable number of decimal places.
5. Compare your BMI result to commonly used adult categories to get a general sense of where you fall, keeping in mind that BMI is one data point, not a diagnosis.
6. Optionally, record your BMI periodically alongside other metrics (waist circumference, body fat estimates, blood pressure, lab values) to track trends over time.

Inputs explained

Weight

Your body weight in kilograms. If your scale reads in pounds, divide by 2.20462 to convert to kilograms (for example, 150 lbs ≈ 68.04 kg). We recommend using a recent measurement taken under similar conditions (same time of day, similar clothing).

Height

Your height in centimeters. If you know your height in feet and inches, convert to inches (feet × 12 + inches) and then multiply by 2.54 to get centimeters. For example, 5 ft 9 in → 69 in → 175.26 cm.

When to use it

• Getting a quick, standardized number that summarizes weight relative to height for use in basic health questionnaires, insurance forms, or research surveys.
• Tracking BMI alongside other health indicators as you work on weight loss, muscle gain, or other body‑composition goals, paying more attention to trends over time than to a single data point.
• Translating height and weight from a medical visit into BMI for fitness apps, personal records, or coaching dashboards that reference BMI categories.
• Providing a starting point for discussions with healthcare providers about weight‑related risks, while acknowledging BMI’s limitations in muscular, older, or certain ethnic populations.
• Using BMI in models or calculators that require a standardized body‑size metric for rough risk stratification (for example, some epidemiological tools).

Tips & cautions

• Use consistent measurement methods each time you calculate BMI. Measuring weight at the same time of day with similar clothing helps reduce normal day‑to‑day fluctuations.
• Remember that BMI does not distinguish between muscle and fat. Athletes and very muscular individuals may have a high BMI while still having low body fat.
• For a fuller picture, consider combining BMI with other measures such as waist circumference, waist‑to‑height ratio, body fat percentage estimates, blood pressure, blood sugar, and cholesterol.
• Be cautious about drawing strong conclusions from small changes in BMI. A difference of a few tenths of a point may reflect normal variation rather than a meaningful change in health.
• Use BMI categories as a conversation starter, not a label. Individual health risk can vary widely within any given BMI range.
• BMI does not directly measure body fat, lean mass, or fat distribution. Two people with the same BMI can have very different body compositions and health profiles.
• The standard adult BMI categories were developed based on population‑level data and may not perfectly reflect risk for every individual, especially certain ethnic groups, older adults, or people with high muscle mass.
• This calculator is intended for adults. BMI interpretation is different for children and teens, where age‑ and sex‑specific growth charts are typically used instead of fixed cutoffs.
• BMI does not account for factors like fitness level, diet quality, smoking status, metabolic health, or family history, all of which are important for understanding individual health risk.
• Because it is a simple ratio, BMI should not be used as the sole basis for major medical decisions, diagnoses, or treatment plans.

Worked examples

Deep dive

FAQs

Does BMI account for muscle mass?

No. BMI uses only height and weight, so it cannot distinguish between muscle, bone, and fat. As a result, very muscular individuals or strength athletes may have a high BMI but low body fat. In those cases, body‑composition testing and professional evaluation are more informative than BMI alone.

Should BMI guide medical decisions?

BMI should not be the sole basis for medical decisions. It is best used as a screening tool to flag potential weight‑related concerns. Always discuss your BMI and overall health with a qualified healthcare provider who can consider your full medical history, exam findings, and additional tests.

Is BMI accurate for children and teenagers?

Standard adult BMI cutoffs are not used for children and teens. Pediatric BMI is typically interpreted using age‑ and sex‑specific growth charts. If you have questions about a child’s BMI, consult a pediatrician or other qualified healthcare professional.

Can BMI be different across ethnic groups?

Yes. Research suggests that the relationship between BMI, body fat, and health risk can differ across ethnic groups. Some populations may experience higher risk at lower BMI thresholds, while others may tolerate higher BMI with different patterns of risk. This is one reason why BMI should not be treated as a universal, one‑size‑fits‑all measure.

How often should I check my BMI?

There is no single right frequency. Many people check BMI occasionally—when starting a health program, at yearly checkups, or monthly while monitoring weight goals. Focus more on overall trends and your healthcare provider’s guidance than on minor day‑to‑day fluctuations.

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