Body mass index (BMI) is the number doctors, insurers and fitness apps use as a first check of whether your weight is in a healthy range for your height. This BMI calculator works out your BMI from feet, inches and pounds or from centimeters and kilograms. It also shows your category, the healthy weight range for your height and how many pounds separate you from it.
Quick answer: BMI = 703 × weight (lb) ÷ height (in)², or kg ÷ m². A healthy adult BMI is 18.5–24.9. Someone 5 ft 9 in tall and 160 lb has a BMI of 23.6 (healthy). At 5 ft 9 in, a healthy weight is about 125–169 lb.
How to calculate your BMI
- Choose U.S. units (feet, inches, pounds) or Metric units (centimeters, kilograms).
- Enter your height and weight. Weigh yourself in the morning, without shoes, for the most consistent result.
- Press Calculate. You will see your BMI, your category, the healthy weight range for your height, how much you would need to gain or lose to reach it, and two extra indexes (BMI Prime and the ponderal index).
BMI formula
| Units | Formula | Example |
|---|---|---|
| U.S. | 703 × weight (lb) ÷ height (in)² | 703 × 160 ÷ 69² = 23.6 |
| Metric | weight (kg) ÷ height (m)² | 70 ÷ 1.75² = 22.9 |
| BMI Prime | BMI ÷ 25 | 23.6 ÷ 25 = 0.94 |
The number 703 converts pounds and inches into the metric kilograms-per-square-meter scale, so both formulas give the same BMI.
BMI categories for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity (class 1) |
| 35.0 – 39.9 | Obesity (class 2) |
| 40.0 and above | Severe obesity (class 3) |
These categories come from the CDC and the World Health Organization and apply to adults 20 and older.
Healthy weight for your height
The chart below the calculator lists the healthy weight range for every height from 4 ft 10 in to 6 ft 4 in. A few common heights:
| Height | Healthy weight (BMI 18.5–24.9) | Overweight from |
|---|---|---|
| 5 ft 0 in | 95–127 lb | 128 lb |
| 5 ft 4 in | 108–145 lb | 146 lb |
| 5 ft 6 in | 115–154 lb | 155 lb |
| 5 ft 9 in | 125–169 lb | 169 lb |
| 6 ft 0 in | 136–184 lb | 184 lb |
BMI examples
Example 1: 5 ft 9 in, 160 lb
Height = 69 in. BMI = 703 × 160 ÷ 4,761 = 23.6, a healthy weight. The healthy range at this height is 125.3–168.6 lb.
Example 2: 5 ft 4 in, 180 lb
Height = 64 in. BMI = 703 × 180 ÷ 4,096 = 30.9, obesity class 1. The top of the healthy range is 24.9 × 4,096 ÷ 703 ≈ 145.1 lb, so reaching a BMI under 25 means losing about 34.9 lb.
Example 3: 175 cm, 70 kg
BMI = 70 ÷ 1.75² = 22.9. The healthy range at 175 cm is 56.7–76.3 kg.
How to read your result
- BMI is a screening tool. It flags a possible weight problem; it does not measure body fat. To estimate body fat, use the body fat calculator with a tape measure.
- Muscle weighs more than fat. Athletes and people who lift weights often land in the overweight range with little body fat.
- Waist size adds context. A waist over 40 in for men or 35 in for women raises health risk at any BMI.
- Age and ethnicity matter. Some people of Asian descent face higher risk at lower BMIs, and older adults may be healthier slightly above 25.
- Changing your weight? The calorie calculator shows how many calories you need to lose or gain weight at a steady pace.
- Measurements in metric? Convert them with the length converter and weight converter.
Common mistakes
- Using total inches incorrectly. 5 ft 9 in is 69 in, not 59. The calculator takes feet and inches separately to avoid this.
- Applying adult categories to children. Under 20, BMI must be compared with age- and sex-specific percentiles.
- Treating one reading as a verdict. Weight changes through the day; track the trend instead.
This calculator is for general information and is not medical advice. Talk to your doctor about what a healthy weight means for you.
Frequently asked questions
How do you calculate BMI?
BMI is weight divided by height squared. In metric units it is kilograms ÷ meters². In U.S. units, multiply pounds by 703 and divide by inches squared. For someone 5 ft 9 in (69 in) tall who weighs 160 lb: 703 × 160 ÷ 69² = 23.6.
What is a healthy BMI for adults?
For adults 20 and older, a BMI from 18.5 to 24.9 is considered a healthy weight. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or higher is obesity, which is further split into class 1 (30–34.9), class 2 (35–39.9) and class 3 (40 and above).
What is a healthy weight for 5 ft 6 in?
At 5 ft 6 in (66 in), a BMI of 18.5 to 24.9 corresponds to roughly 115 to 154 lb. You become overweight by BMI at about 155 lb. The chart on this page lists the healthy range for every height from 4 ft 10 in to 6 ft 4 in.
Is BMI accurate?
BMI is a quick screening number, not a diagnosis. It does not separate muscle from fat, so very muscular people can score as overweight, and older adults who have lost muscle can score as healthy while carrying extra fat. Waist circumference and a doctor’s assessment give a fuller picture.
Is BMI different for men and women?
No. Adult BMI uses the same formula and the same categories for men and women. Women tend to have a higher body fat percentage at the same BMI, but the cut-off points are identical.
Can I use this BMI calculator for children?
For children and teens aged 2 to 19, the BMI number is calculated the same way but interpreted with CDC growth charts that compare it with other children of the same age and sex. Use a BMI-for-age percentile instead of the adult categories on this page.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the upper limit of the healthy range. A value below 1.0 means you are under that limit; 1.2 means your BMI is 20% above it. A BMI of 23.6 gives a BMI Prime of 0.94.
How much weight do I need to lose to reach a healthy BMI?
Multiply 24.9 by your height in inches squared and divide by 703 to get the top of the healthy range in pounds, then subtract it from your weight. At 5 ft 4 in and 180 lb, the limit is about 145.1 lb, so the difference is 34.9 lb. The calculator shows this number for you.
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