🩺 Health calculator

BMI Calculator

Calculate your Body Mass Index from height and weight. This free BMI calculator uses the standard WHO formula, shows which BMI category you fall into, and explains what your result actually means for your health β€” not just a number on a chart.

Enter your height and weight

BMI uses the same formula for all adults regardless of age or sex. For a more complete picture, pair BMI with a body fat percentage or waist-to-hip ratio measurement.

BMI categories (WHO)

Under 18.5 β€” Underweight
18.5–24.9 β€” Normal weight
25.0–29.9 β€” Overweight
30.0 and above β€” Obese

Limitations to know

BMI does not distinguish muscle from fat. Athletes and older adults may get misleading results. Use it as a screening tool, not a diagnosis.

Tip: if you are very muscular, BMI will likely overestimate your body fat. A body fat percentage calculator gives a more accurate picture in that case.
This calculator is for informational purposes only. BMI is a screening tool and does not diagnose health conditions. Consult a healthcare professional for medical advice.

What is BMI?

Body Mass Index is a number calculated from your height and weight. It is one of the most widely used screening tools in medicine because it is fast, free, and requires no equipment. A BMI in the "normal" range correlates with lower risk of weight-related conditions like type 2 diabetes, cardiovascular disease, and certain cancers.

BMI was developed in the 1830s and remains useful as a population-level screening metric. For individuals, especially those with high muscle mass or different body frame sizes, it has well-known limitations β€” which is why doctors use it alongside other measurements.

BMI formula

There are two versions depending on the unit system you use:

Metric: BMI = weight (kg) Γ· heightΒ² (m)
Imperial: BMI = 703 Γ— weight (lb) Γ· heightΒ² (in)

For example, a person who is 5'9" (175 cm) and weighs 160 lb (72.6 kg):

Height in metres: 175 Γ· 100 = 1.75 m
BMI = 72.6 Γ· (1.75 Γ— 1.75) = 72.6 Γ· 3.0625 = 23.7

How to use this BMI calculator

  1. Choose imperial (feet, inches, pounds) or metric (centimetres, kilograms).
  2. Enter your height. For imperial, enter feet and inches separately.
  3. Enter your current weight.
  4. Click Calculate BMI to see your result and category.
  5. Read the interpretation to understand what your BMI means in plain English.
  6. Check the "What to do next" section for the most useful follow-up step.

BMI categories explained

The WHO defines four main BMI ranges for adults:

Under 18.5 β€” Underweight. May indicate nutritional deficiency or other health issues. Consult a doctor.
18.5–24.9 β€” Normal weight. Associated with the lowest risk of weight-related conditions.
25.0–29.9 β€” Overweight. Slightly elevated risk for some conditions. Diet and activity adjustments often help.
30.0 and above β€” Obese. Higher risk for type 2 diabetes, cardiovascular disease, and other conditions. Medical guidance recommended.

Example calculation

A person who is 5 feet 6 inches tall and weighs 155 pounds:

Height: 5'6" = 66 inches total
BMI = 703 Γ— 155 Γ· (66 Γ— 66) = 108,965 Γ· 4,356 = 25.0
Category: Overweight (just at the boundary)
Healthy weight range for 5'6": approximately 115–154 lb

This person is 1 pound above the upper limit of the normal range. A small change in diet or activity level could bring them back into the normal range β€” which is a more useful insight than just seeing the number 25.0.

BMI limitations

BMI is useful but has real limitations that are worth knowing:

  • Muscle vs fat: A muscular athlete may have a high BMI despite very low body fat. BMI cannot tell the difference.
  • Age: Older adults tend to have more fat relative to muscle at the same BMI as younger adults.
  • Sex: Women typically have more body fat than men at the same BMI.
  • Ethnicity: Some research suggests different BMI thresholds may be more appropriate for Asian populations.
  • Distribution: BMI does not account for where fat is stored. Abdominal fat carries higher risk than fat in other areas.

Frequently asked questions

What is a healthy BMI for adults?

The WHO defines 18.5 to 24.9 as the normal range for adults. This range is associated with the lowest risk of weight-related health conditions. However, BMI is one data point β€” not a complete picture of health.

Does BMI apply to children?

Standard BMI categories do not apply to children and teens. For those under 18, BMI-for-age percentiles using CDC growth charts are used instead. A separate BMI-for-age calculator is more appropriate in those cases.

Can I have a high BMI and still be healthy?

Yes. Some people with high BMI β€” particularly athletes with high muscle mass β€” have low body fat and strong metabolic health markers. BMI alone does not diagnose poor health. Blood pressure, blood sugar, cholesterol, and other factors matter too.

How is BMI different from body fat percentage?

BMI is calculated from height and weight only. Body fat percentage measures how much of your total weight is fat versus lean mass. Body fat percentage is more accurate for individuals but requires more data to calculate β€” measurements, skinfold calipers, or DEXA scanning.

What should I do if my BMI is outside the normal range?

Start by understanding whether the result reflects actual body composition. If you are not highly muscular and your BMI is above 25 or below 18.5, it is worth discussing with a doctor or registered dietitian. Small, consistent lifestyle changes often have a bigger impact than drastic measures.

Related health calculators

These tools pair naturally with BMI to give a more complete picture of your health.

BMR Calculator Find your Basal Metabolic Rate β€” the calories your body burns at rest. The natural next step after BMI. Calorie Deficit Calculator Calculate the deficit needed to reach your target weight at a healthy pace. Caffeine Half-Life Calculator See how long caffeine stays active in your system β€” useful for sleep and energy management. Cardiac Output Calculator Calculate cardiac output from heart rate and stroke volume for clinical reference.

Disclaimer

This BMI calculator is for informational and educational purposes only. BMI is a general screening metric and does not constitute medical advice, diagnosis, or treatment. Results should not replace consultation with a qualified healthcare professional. Individual health decisions should be made with appropriate medical guidance.