Get your number and see where you fall on the color meter. BMI = weight (kg) ÷ height² (m²).
Note: BMI is a screening tool, not a diagnosis. Ranges differ for children and some athletes.
Body Mass Index (BMI) is a quick way to check whether your weight is appropriate for your height. It gives you a single number that falls into a category—underweight, healthy, overweight, or obese—which helps flag potential health risks. Doctors, coaches, and dietitians use BMI as a screening tool: it doesn’t diagnose illness or measure body fat directly, but it can indicate when to take a closer look at your lifestyle and health markers.
Our free BMI Calculator above does the math instantly. This guide explains how BMI works, the science and formulas behind it, where its limits are, and practical steps to move toward a healthier range—covering diet, exercise, sleep, and habits.
Someone weighing 70 kg and 1.75 m tall has BMI = 70 ÷ (1.75 × 1.75) = 22.9, which falls in the healthy range. The calculator handles metric or imperial inputs and converts feet/inches automatically.
You can invert the formula to estimate a healthy weight range for a given height. For adults, a BMI between 18.5 and 24.9 is considered “healthy.”
| BMI Range | Category | Notes |
|---|---|---|
| Below 18.5 | Underweight | Consider nutrition review; can indicate low muscle or deficiencies |
| 18.5 – 24.9 | Healthy | Lowest risk of most weight-linked conditions |
| 25.0 – 29.9 | Overweight | Elevated risk for diabetes, hypertension, CVD |
| 30.0 – 34.9 | Obesity I | Increased health risks; structured plan recommended |
| 35.0 – 39.9 | Obesity II | Severe health risks; medical guidance suggested |
| 40.0+ | Obesity III | Very severe risk; multidisciplinary care beneficial |
Underweight (<18.5): may reflect inadequate calorie/protein intake, nutrient deficiencies, or a medical issue. Focus on nourishing, calorie-dense foods and strength training (see below).
Healthy (18.5–24.9): generally associated with the lowest risk of weight-related diseases. Keeping steady habits—balanced meals, regular activity, good sleep—helps maintain it.
Overweight (25–29.9): risk begins to rise for conditions like type 2 diabetes and cardiovascular disease. Small, sustainable changes often deliver strong results here.
Obese (≥30): higher risk of chronic conditions. A structured, supportive plan (dietary adjustments, activity, behavioral strategies) and professional guidance can be very effective.
Because of these limits, BMI is best paired with waist circumference, body fat percentage, and clinical indicators (blood pressure, glucose, lipids).
Combine BMI with these metrics and routine health checks (blood pressure, lipids, glucose) for the full picture.
For most adults, BMI is a helpful first check. It’s not perfect—muscular people may show “overweight” despite low body fat—so pair it with other measures.
Underweight: <18.5; Healthy: 18.5–24.9; Overweight: 25–29.9; Obesity: ≥30.
Every 1–2 months works for most. Track more frequently if you’re on a new program.
No. Children and teens use age- and sex-specific percentiles.
For weight loss, ~0.5–1 kg per week. For weight gain, add calories gradually while strength training.
Some populations face higher metabolic risk at lower BMI values. Discuss personalized targets with your clinician.
BMI is a simple, fast way to screen weight relative to height. Use it as a starting point, not the final verdict. Combine your BMI with other measures and healthy habits—balanced meals, regular activity, good sleep, and stress management. Re-check periodically with the calculator above to stay on track, and consider professional guidance if your BMI is very high or very low.