BMI Calculator

Understanding BMI and how to use it well

Body Mass Index (BMI) estimates the relationship between your weight and height. It’s calculated by dividing weight by height squared and is widely used as a quick screening tool for adults. While BMI cannot distinguish muscle from fat, it reliably tracks broad changes in weight relative to height and is simple enough to check at home. Think of it as a starting point that becomes more useful when paired with other observations like waist circumference, strength or endurance, and how you feel day to day.

What your result means

• < 18.5: Underweight - may reflect low intake, underlying illness, or a naturally small frame. If unintended, consider speaking with a clinician and reviewing your diet, training, and recovery.
• 18.5–24.9: Healthy - a broad zone that includes many body types. Pair this with waist measurements and performance goals to decide whether to maintain, gain, or lean out.
• 25–29.9: Overweight - BMI suggests weight relative to height is above the healthy range. Waist size, blood pressure, and lab work add helpful context for next steps.
• ≥ 30: Obesity - higher likelihood of health risks on average. Small, sustainable changes to food choices, activity, and sleep can make a big difference over time.

Healthy weight range for your height

The healthy range in our calculator is derived from BMI values of 18.5 to 25. The tool converts that band into a weight range for your specific height, so you can see where you currently sit, and how far you are from the edge of the range. If you’re above the upper bound, the page shows the approximate amount of weight to lose to reach a BMI of 25. If you’re below the lower bound, it shows the weight to gain to reach a BMI of 18.5.

Why we also show BMI Prime and Ponderal Index

BMI Prime expresses BMI relative to the healthy upper boundary (25). A value of 1.00 equals BMI 25. Numbers under 1.00 are below that boundary; numbers above 1.00 are over it. Ponderal Index (PI) divides weight by height cubed instead of squared. It is occasionally used for very tall or very short adults and in neonatal settings. These extra metrics aren’t required to make decisions, but they can help compare bodies of different heights.

Getting consistent measurements

• Weigh yourself after waking and using the restroom, before eating or drinking.
• Measure height barefoot, standing tall with your heels, buttocks, and upper back against a wall.
• Track a weekly average of weight to smooth daily swings from hydration and food timing.

Putting numbers into action

• Anchor protein intake and include foods you genuinely enjoy to make consistency easier.
• Move most days-walking, climbing stairs, cycling, lifting, or classes you like.
• Sleep is a powerful multiplier. Aim for a regular schedule and a dark, quiet room.
• Evaluate progress every 2–3 weeks and adjust gradually rather than making big swings.

Limitations to keep in mind

BMI doesn’t directly measure body fat. Muscular people can score in the “overweight” or even “obesity” ranges despite having low body fat, while some people with lower BMI may still carry more visceral fat than is ideal. That’s why pairing BMI with waist size, body-fat estimates, and how you perform and feel provides a clearer picture. For children and teens, BMI is interpreted using age- and sex-specific percentiles rather than adult cutoffs; this tool is designed for adults aged 20+.

Informational use only and not a medical diagnosis. If you have a medical condition or concerns about weight or nutrition, please consult a qualified professional.