BMI Calculator: Check Your Body Mass Index and Healthy Weight Range
Body Mass Index (BMI) is the most widely used first-line screening tool for weight-related health risk. Our free BMI calculator converts your height and weight into a single number, classifies it using World Health Organization categories, and shows the exact healthy weight range for your height — in imperial or metric units.
How the BMI Calculator Works
BMI compares your weight to your height with one simple formula:
BMI = weight (kg) / height² (m²)
If you prefer imperial units, the equivalent is 703 × weight (lb) / height² (in²) — the calculator handles the conversion automatically, so the result is identical either way. A person who is 5'10" (178 cm) and 160 lb (72.6 kg) has a BMI of about 22.9, comfortably inside the healthy band.
WHO BMI Categories
| Category | BMI range | |---|---| | Underweight | Below 18.5 | | Normal weight | 18.5 – 24.9 | | Overweight | 25.0 – 29.9 | | Obesity Class I | 30.0 – 34.9 | | Obesity Class II | 35.0 – 39.9 | | Obesity Class III | 40 and above |
These thresholds were set by the WHO and are used by doctors worldwide. Research consistently shows health risk rises steeply above a BMI of 30, and also increases below 18.5, where nutritional deficiency and bone loss become concerns.
Your Healthy Weight Range
One limitation of a single BMI number is that it hides the range it came from. That is why this calculator also reports the weight band that corresponds to a healthy BMI (18.5–24.9) at your height. For someone 5'10", that works out to roughly 129–173 lb. If your current weight sits inside this band, your BMI is healthy by definition.
Worked Example
Consider a 30-year-old who is 70 inches tall and weighs 200 lb:
- Convert: 70 in × 0.0254 = 1.78 m; 200 lb × 0.4536 = 90.7 kg
- Square height: 1.78² = 3.16 m²
- Divide: 90.7 / 3.16 = BMI 28.7 — Overweight
To reach the healthy band, this person would need to weigh between 132 and 178 lb, meaning a loss of roughly 22–68 lb depending on their goal.
BMI Limitations: When It Misleads
BMI was designed as a population screening tool, and for individuals it has well-documented blind spots:
- Muscular people — muscle is denser than fat, so athletes are often classified "overweight" while carrying very little fat
- Adults over 65 — a slightly higher BMI (23–28) is associated with the best survival in this group
- Children and teens — BMI must be plotted on age-and-sex percentile charts, not adult cutoffs
- Pregnancy — BMI is meaningless during pregnancy and should not be used
- Different ethnic groups — some populations (e.g., South Asian) develop metabolic risk at lower BMIs, and several countries use adjusted thresholds
When BMI and reality disagree, body composition is the tiebreaker — our body fat calculator estimates composition from tape measurements instead of assuming an average body.
What To Do With Your Result
A healthy BMI is encouraging, but it is only a snapshot. Pair it with waist circumference (risk rises above 40 in / 102 cm for men and 35 in / 88 cm for women), blood pressure, and lab markers for a complete picture. If your BMI falls outside the healthy band, even a 5–10% weight change measurably improves blood pressure, blood sugar, and cholesterol — you do not need to reach the "perfect" number to benefit. A sensible next step is our TDEE calculator to find the daily calorie intake that supports your goal.
This calculator is a screening tool, not a medical diagnosis. Consult a healthcare professional before making significant changes to diet or exercise.