# What is my BMI?

Computes body mass index (weight in kilograms divided by height in metres squared) and its CDC adult category, or the weight or height that gives a chosen BMI.

- Page: https://www.acalculator.org/health/bmi-calculator
- JSON spec: https://www.acalculator.org/health/bmi-calculator.json
- Version: dc0e1768df38

## Default answer

Example with the default inputs (Height 5 ft 10 in, Weight 160 lb): At 160 lb, your BMI is 23, which is in the Healthy weight range for adults.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| height | Height | Your height without shoes. |
| weight | Weight | Your body weight. |
| bmi | BMI | Body mass index: weight in kilograms divided by height in metres squared. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| height | Height | Your height without shoes. |
| weight | Weight | Your body weight. |
| bmi | Your BMI | Body mass index: weight in kilograms divided by height in metres squared. |
| category | Category | The CDC adult BMI category: underweight, healthy weight, overweight, or obesity. |
| healthyMin | Healthy weight from | The lowest weight whose BMI shows as 18.5 at this height: BMI 18.45 × height². |
| healthyMax | Healthy weight up to | The weight at the top of the healthy range for this height: BMI 24.95 × height² (just under). |

## Method

BMI = weight ÷ height², with weight in kilograms and height in metres (CDC).

## Assumptions

- The categories are the CDC adult categories, for people aged 20 and older. Children and teens use BMI-for-age percentiles instead.
- BMI is a screening measure. It does not measure body fat directly and does not diagnose health.
- The category is read from the BMI rounded to one decimal place, as shown: 18.5 to 24.9 is healthy weight, so 24.96 (rounded to 25.0, shown as 25) is overweight.
- The healthy weight range is the weights whose BMI shows as 18.5 to 24.9 at your height: BMI 18.45 to just under 24.95.

## Worked examples

1. weight = 68.038856, height = 1.651 gives bmi = 24.96, category = Overweight. Source: CDC English formula: 150 lb ÷ (65 in)² × 703 = 24.96 (weight and height given here in kg and m: 1 lb = 0.45359237 kg, 1 in = 0.0254 m); rounded to 25.0, overweight in the NHLBI one-decimal table (25.0 to 29.9).
2. weight = 70, height = 1.75 gives bmi = 22.857143, healthyMin = 56.503125, healthyMax = 76.409375. Source: hand calculation in content.mdx: 70 ÷ 1.75² = 22.86; 18.45 × 1.75² = 56.50 kg; 24.95 × 1.75² = 76.41 kg.
3. bmi = 18.5, height = 1.7526 gives weight = 56.824725. Source: CDC adult BMI categories: at 5 ft 9 in, 125 lb is the start of the healthy range; 18.5 × 1.7526² = 56.82 kg = 125.3 lb (hand calculation in content.mdx).
4. weight = 90, bmi = 30 gives height = 1.732051, category = Obesity. Source: hand calculation in content.mdx: height = √(90 ÷ 30) = √3 = 1.732 m; BMI 30 is obesity (CDC).

## FAQ

### How is BMI calculated?

BMI is your weight in kilograms divided by your height in metres squared. In pounds and inches, it is weight ÷ height² × 703. For example, 150 lb at 5 ft 5 in (65 in) is 150 ÷ 65² × 703 = 24.96, which rounds to 25.0 (the calculator shows 25).

### What do the BMI categories mean?

For adults 20 and older, the CDC uses these categories. Underweight is a BMI under 18.5. Healthy weight is 18.5 to less than 25. Overweight is 25 to less than 30. Obesity is 30 or more, split into class 1 (30 to less than 35), class 2 (35 to less than 40) and class 3 (40 or more). The calculator reads the category from the BMI rounded to one decimal place, as the NHLBI table does (18.5 to 24.9 is healthy weight), so the number you see and its category always agree.

### What is a healthy weight for my height?

The weights that give a BMI of 18.5 to 24.9 (rounded to one decimal) at your height: 18.45 × height² up to just under 24.95 × height², with height in metres and weight in kilograms. At 5 ft 9 in, that is about 125 to 168 pounds, as on the CDC chart.

### Can I use this calculator for children or teens?

No. For people under 20, the CDC compares BMI with others of the same age and sex using BMI-for-age percentiles. The adult categories here do not apply.

### Does BMI measure body fat?

Not directly. BMI is a quick screening measure based only on height and weight. Two people with the same BMI can have different amounts of body fat, for example an athlete with a lot of muscle. A health care provider can do further checks.

## Sources

- Centers for Disease Control and Prevention, Adult BMI Categories. https://www.cdc.gov/bmi/adult-calculator/bmi-categories.html
- Centers for Disease Control and Prevention, Adult BMI Calculator. https://www.cdc.gov/bmi/adult-calculator/index.html
- Centers for Disease Control and Prevention, Growth Chart Training, Calculating BMI Using the English System (weight ÷ height² × 703). https://www.cdc.gov/growth-chart-training/hcp/using-bmi/calculating-bmi.html
- National Heart, Lung, and Blood Institute, Calculate Your Body Mass Index (BMI categories to one decimal: underweight below 18.5, healthy 18.5 to 24.9, overweight 25.0 to 29.9, obesity 30.0 or above). https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm
- NIST SP 811 (2008), Appendix B: 1 lb = 0.45359237 kg and 1 in = 0.0254 m exactly.