BMI Calculator for Adults — Chart, Ranges & Tips
Calculate Body Mass Index
BMI calculator for adults: quick answers, categories & tips
What you’ll see after you calculate
This tool estimates Body Mass Index from your height and weight in either metric or US units. You’ll get your BMI value (kg/m²), the matching adult category (Underweight, Normal, Overweight, Obesity I–III), a healthy weight range for your height, and a pointer on the color bar so you can spot your position instantly.
How to get a reliable result
Measure height without shoes and use a recent body weight, ideally in the morning after using the bathroom. Fill in every field for the unit system you choose. Switching between metric and US is fine; each set of inputs is kept separate to avoid conversion mistakes.
How to read your number
Underweight often pairs with low energy availability and can warrant a check-in on food intake, recovery, and bone health. A Normal result is common for many adults; keep an eye on waist size and fitness trends rather than single readings. Overweight suggests reviewing everyday habits around movement, sleep, and food quality; modest, sustained changes tend to work better than short, extreme pushes. Obesity raises cardiometabolic risk, especially with larger waist circumference; steady improvements in activity, diet, and sleep can move health markers even before weight shifts much.
Small actions that compound
Walk more across the day, aim for two or three strength sessions weekly, and build meals around protein, fiber, and minimally processed foods. Seven to nine hours of sleep supports appetite regulation and training recovery. Track a few behaviors you control—steps, workouts, bedtime—alongside outcomes like weight and waist size so you see cause and effect over time.
Limits and exceptions
- Not a body-fat test: muscular people can score high BMI despite low body fat, while others with lower BMI but high visceral fat may still carry risk.
- Adults only: children need age- and sex-specific percentiles; pregnancy and elite sport require tailored methods.
- Daily noise: hydration and meals move scale weight; use weekly averages or monthly trends for decisions.
Formulas at a glance
Metric formula: BMI = weight (kg) ÷ height² (m²). Example: 70 ÷ (1.75 × 1.75) = 22.9.
US formula: BMI = 703 × weight (lb) ÷ height² (in²). Example: 154 × 703 ÷ (69 × 69) ≈ 22.7.
The calculator also shows BMI Prime (your BMI divided by 25). A value near 1.00 is the upper end of the Normal range; below 1.00 is below that threshold, above 1.00 is above it.
| Category | BMI (kg/m²) | Notes |
|---|---|---|
| Severe Thinness | < 16.0 | Clinical underweight |
| Moderate Thinness | 16.0–16.9 | Underweight |
| Mild Thinness | 17.0–18.4 | Low-normal threshold |
| Normal | 18.5–24.9 | Typical healthy range |
| Overweight | 25.0–29.9 | Check waist and lifestyle |
| Obesity I | 30.0–34.9 | Elevated metabolic risk |
| Obesity II | 35.0–39.9 | High risk |
| Obesity III | ≥ 40.0 | Very high risk |
Interpret BMI alongside waist-to-height ratio, fitness, and clinical markers.
BMI calculator FAQs
What BMI range is considered healthy?
For most adults, a healthy BMI range is 18.5–24.9. Add waist size and fitness context for a fuller picture.
Is BMI useful for athletes?
Muscular athletes can read high BMI despite low body fat. Pair BMI with waist-to-height ratio and performance metrics.
Which units should I choose?
Use metric or US—the calculator applies the correct formula in either case.
What are the obesity classes?
Obesity I (30–34.9), Obesity II (35–39.9), Obesity III (≥40).
How can I lower BMI safely?
Favor sustainable habits: modest calorie deficit, protein and fiber, strength training, daily movement, and consistent sleep.