BMI Calculator
Calculate your Body Mass Index — a quick screening tool that uses your weight and height to estimate whether you’re in a healthy weight range.
Your Results
Weight at Different BMI Levels
| BMI | Category | Weight | Difference |
|---|
Go Beyond BMI — Track What Actually Matters
BMI is a starting point. The app tracks your real calorie intake, macros, and weight trends — so you can actually reach your healthy weight, not just calculate it.
What is BMI?
Body Mass Index (BMI) is a simple numerical value calculated from your weight and height. It was developed in the 1830s by Belgian mathematician Adolphe Quetelet as a way to quickly assess body weight relative to height across populations.
Today, BMI is used by the World Health Organization (WHO) and healthcare providers worldwide as a screening tool to categorize individuals into weight categories: underweight, normal weight, overweight, and obese. While it doesn’t measure body fat directly, it correlates with more direct measures of body fatness in most people.
How BMI is Calculated
The BMI formula is straightforward:
For example, if you weigh 75 kg and are 1.75 m tall:
If you’re using imperial units (pounds and inches), the formula includes a conversion factor:
This calculator handles all unit conversions automatically — just enter your weight and height in whichever units you prefer.
BMI Categories & Chart
The WHO defines the following BMI categories for adults (age 20+):
| BMI Range | Category | Health Risk |
|---|---|---|
| < 16.0 | Severe Underweight | Very high |
| 16.0 – 16.9 | Moderate Underweight | High |
| 17.0 – 18.4 | Mild Underweight | Moderate |
| 18.5 – 24.9 | Normal Weight | Low |
| 25.0 – 29.9 | Overweight | Moderate |
| 30.0 – 34.9 | Obese Class I | High |
| 35.0 – 39.9 | Obese Class II | Very high |
| ≥ 40.0 | Obese Class III | Extremely high |
These categories apply to adults regardless of gender. For children and teenagers (2–19), BMI is interpreted using age- and sex-specific percentile charts from the CDC, since body composition changes significantly during growth.
BMI for Women vs Men
The BMI formula and categories are identical for men and women. However, body composition differs between genders:
- Women naturally carry more body fat (essential fat ~12% vs ~3% for men) and tend to store fat in the hips and thighs.
- Men typically have more muscle mass and store fat in the abdominal area.
This means two people — one male, one female — with the same BMI may have different body fat percentages. A BMI of 24 might correspond to ~20% body fat in a man but ~28% in a woman. Both are considered healthy, but the composition is different.
For this reason, BMI works best as a population-level screening tool rather than a precise individual assessment.
BMI Limitations
BMI has several well-known limitations:
- Doesn’t distinguish muscle from fat. A muscular athlete and a sedentary person of the same height and weight will have the same BMI, despite very different health profiles.
- Doesn’t account for fat distribution. Abdominal (visceral) fat is more dangerous than subcutaneous fat, but BMI can’t tell where your fat is stored.
- Less accurate at the extremes. Very tall or very short individuals may get misleading results because BMI uses height squared rather than a more nuanced exponent.
- Age and ethnicity matter. Older adults may have more body fat at the same BMI. Some ethnic groups (particularly South Asian and East Asian populations) face higher health risks at lower BMI values.
Bottom line: BMI is a useful starting point for assessing weight status, but it’s not the whole picture. For a more complete understanding of your health, combine BMI with waist circumference, body fat percentage, and your overall fitness level.
Healthy Weight & Ideal Weight
Your healthy weight range is calculated from BMI boundaries (18.5–24.9) applied to your height:
Max healthy weight = 24.9 × height (m)²
This calculator also shows your ideal weight using the Devine formula (1974), which is widely used in clinical settings for medication dosing and as a reference point:
Female: 45.5 + 2.3 × (height in inches − 60)
The Devine formula is gender-specific and gives a single target weight rather than a range. It tends to produce results in the middle of the healthy BMI range, making it a reasonable goal for most people.
BMI vs Body Fat Percentage
While BMI estimates weight status from height and weight alone, body fat percentage directly measures how much of your body mass is fat tissue. Body fat is a more accurate indicator of health risk, but it’s harder to measure (requiring calipers, DEXA scans, or bioelectrical impedance).
Healthy body fat ranges are:
- Men: 10–20% (athletes: 6–13%)
- Women: 18–28% (athletes: 14–20%)
If you know your body fat percentage, our TDEE calculator can use the Katch-McArdle formula to calculate a more accurate Basal Metabolic Rate based on your lean body mass — giving you better calorie and macro targets than BMI alone.
Beyond BMI — Actionable Steps
Knowing your BMI is the first step. Here’s what to do with that number:
- If your BMI is in the healthy range (18.5–24.9): Focus on maintaining your weight through balanced nutrition and regular activity.
- If your BMI is above 25: Calculate your TDEE and create a moderate calorie deficit (300–500 kcal/day) for sustainable weight loss.
- If your BMI is below 18.5: Consult a healthcare professional and focus on nutrient-dense foods to gradually increase weight.
Whatever your starting point, the key is tracking what you eat consistently. AI Food Coach makes this easy — snap a photo of your food on a kitchen scale, and AI calculates exact macros in seconds.