What BMI is
BMI is calculated from your weight and height. It’s commonly used to flag whether someone is likely underweight, in a healthy range, overweight, or obese — as a population-level screening tool.
BMI Calculator
Enter your weight and height in metric or imperial units to estimate your Body Mass Index.
How this calculator works
BMI (Body Mass Index) is a quick screening metric that compares your weight to your height. We convert your inputs into metric units, apply the BMI formula, and show the standard category range.
The formula we use
After converting units (lb → kg, inches/ft → meters), BMI is:
BMI = weight (kg) ÷ [height (m)]²
How to enter height correctly
- cm: enter your height in centimeters (e.g., 175).
- inches: enter total inches (e.g., 69).
- ft + in: enter feet in the first box and inches in the second (e.g., 5 and 9).
Tip: if you select cm or inches, the second height box isn’t needed.
What the categories mean (context)
BMI categories are simple cut-offs. They’re useful for a fast snapshot, but BMI doesn’t directly measure body fat or muscle — so two people with the same BMI can look very different.
If you lift weights or have higher muscle mass, BMI can overestimate “fatness”.
Limitations & when BMI can mislead
- Doesn’t separate muscle vs fat.
- Doesn’t capture fat distribution (waist size matters for health risk).
- Can be less informative for very muscular people, older adults, and some body types.
- Not a medical diagnosis — it’s a screening indicator.
Better “next checks” than BMI alone
- Track waist circumference (health risk relates strongly to abdominal fat).
- Use a body fat % estimate for composition context.
- Compare strength and performance trends over time.
Quick workflow
Enter weight
Select height mode
Enter height
Calculate BMI
Use context tools
BMI is most useful when you treat it as one data point — not a final verdict.
Mini FAQ
Is BMI accurate for athletes or lifters?
Sometimes, but not always. If you have above-average muscle mass, BMI can label you as “overweight” even if your body fat is low. Use BMI alongside measurements like waist circumference or body fat %.
Why does BMI use height squared?
Because body mass tends to scale roughly with the square of height across populations. It’s a simple ratio that works reasonably well as a screening tool, even though it’s not perfect for individuals.
Should I worry about BMI category labels?
Treat them as a signal, not a diagnosis. If your BMI is outside the “healthy” range, check other markers (waist, body fat %, health habits, performance, and how you feel). If you’re unsure, speak with a health professional.
My weight fluctuates daily — will BMI change a lot?
BMI moves with weight, and daily weight can swing due to water, sodium, carbs, stress, and digestion. If you’re tracking progress, compare weekly averages, not single days.
What’s a better goal than “a perfect BMI”?
Better goals are: improving waist measurement, fitness, strength, energy, sleep, and consistency. BMI is useful, but outcomes and habits matter more.
Have more questions? Visit the full FAQs.