Calculate your Body Mass Index (BMI) in seconds. Switch between metric and imperial units, get an easy-to-understand category, and see a healthy weight range for your height.
Tip: If you only know your height in feet/inches or weight in pounds, switch the unit system to Imperial.
BMI stands for Body Mass Index. It’s a simple number that compares your weight to your height. The goal is not to “grade” your body — it’s to create a quick, standardized estimate that helps identify whether your weight is likely to fall in a range that’s associated with higher or lower health risks.
Think of BMI like a traffic-light system: it can flag “maybe worth a closer look.” It’s fast, it’s used widely in healthcare and research, and it’s easy to calculate from two measurements you already know: height and weight. But like any shortcut, it has limits — and you’ll make better decisions if you understand what BMI can (and can’t) tell you.
If you measure height in meters and weight in kilograms, the formula is:
BMI = weight (kg) ÷ [height (m)]²
If you enter your height in centimeters (cm), this calculator converts it to meters automatically by dividing by 100. Squaring height matters because surface area grows roughly with height squared. BMI is a practical approximation that keeps the “weight vs height” relationship in a consistent scale.
If you measure height in inches and weight in pounds, BMI uses a conversion factor:
BMI = 703 × weight (lb) ÷ [height (in)]²
The number 703 isn’t “magic” — it’s just the constant that converts pounds and inches into the same scale as the metric formula. This calculator handles it automatically, so you can focus on the meaning of the result.
Most BMI tools for adults use category cutoffs like these:
These ranges are used for screening and broad guidance. They are not a diagnosis. Your actual risk depends on other factors like fat distribution (where you store fat), fitness level, sleep, stress, family history, and medical conditions.
Example 1 (metric): Height = 175 cm, Weight = 72 kg. Convert height to meters: 175 cm → 1.75 m. Then: BMI = 72 ÷ (1.75²) = 72 ÷ 3.0625 ≈ 23.5. That falls in the Normal weight range.
Example 2 (imperial): Height = 5 ft 9 in (69 inches), Weight = 160 lb. BMI = 703 × 160 ÷ (69²) = 112,480 ÷ 4,761 ≈ 23.6. Again, that’s typically classified as Normal weight.
If your BMI looks surprisingly high or low, the most common cause is a unit mix-up. Double-check that you entered height in cm (not meters) for metric, and in ft/in for imperial.
This calculator also shows a healthy weight range for your height. It does this by “reversing” the BMI formula. For a given height, it calculates the weight that would produce BMI 18.5 (low end) and BMI 24.9 (high end).
In metric terms, if height is h meters and target BMI is b, then: weight = b × h². At 1.75 m: low weight = 18.5 × 1.75² ≈ 56.6 kg; high weight = 24.9 × 1.75² ≈ 76.2 kg.
This range is meant to be a quick reference. It doesn’t account for muscle mass, bone density, or body composition. If you lift weights or have a naturally muscular build, your healthiest weight may be above this range while still being healthy.
BMI is most useful when you treat it as one signal, not the whole story. Here are practical ways to use it without overreacting:
Because BMI is a height-to-weight ratio, it cannot tell whether weight comes from fat, muscle, water, or bone. This creates well-known edge cases:
If your BMI category doesn’t match how you look or feel, that’s not a reason to ignore health — it’s a reason to measure more directly (waist ratio, body fat estimate, or professional guidance).
BMI is a starting point. The best “next step” depends on your goal:
In other words: BMI gives you a number. Your habits create the outcome.
BMI is useful for many adults as a quick screening estimate, but it can misclassify muscular people and some older adults. Use it as a guide, not a diagnosis.
For many adults, 18.5–24.9 is considered the typical “normal weight” BMI range. Your personal healthiest range can vary based on body composition and medical context.
Not automatically. A BMI just over 25 could reflect muscle or mild weight gain. Check waist size, fitness level, and trends over time before jumping to conclusions.
BMI uses height squared. A small height input difference can noticeably change BMI, especially if the height entry is off by an inch or two.
BMI is not designed for pregnancy. If you’re pregnant, consult your clinician for appropriate weight guidance.
The formula is the same, but men and women may have different body fat distribution. BMI is still useful as a quick estimate, but body composition measures can be more informative.
Weekly or monthly is usually enough. Daily weigh-ins are noisy because weight naturally fluctuates with water and food.
For fat distribution: waist-to-height ratio. For body composition: body fat percentage estimates. For health: blood pressure, lipids, fitness, and habits all matter.
Disclaimer: This tool provides general information only and is not medical advice. If you have health concerns, consult a qualified professional.