Runner Tools
BMI Calculator
Body mass index from pounds or kilograms, with the CDC adult categories and the healthy weight range for your height — plus an honest look at what BMI cannot tell an endurance athlete.
How to use it
- Choose pounds with feet and inches, or kilograms with centimeters.
- Enter your height and a recent measured weight.
- Read your BMI, the CDC adult category it falls into, and the weight range that would correspond to a BMI of 18.5 to 24.9 at your height.
The math
BMI compares weight to height squared. With metric units, BMI equals weight in kilograms divided by height in meters squared (the calculator converts your centimeters first). With pounds and inches, the standard formula is:
BMI = 703 × weight (lb) ÷ height (in)²
Worked example: 5 ft 9 in is 69 inches, and 69² = 4,761, so 154 lb gives:
- 703 × 154 ÷ 4,761 ≈ 22.7 — in the healthy weight range
- Metric check: 175 cm and 70 kg gives 70 ÷ 1.75² ≈ 22.9, the same category
CDC adult categories
| Category | BMI range (kg/m²) |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 to under 25 |
| Overweight | 25 to under 30 |
| Obesity | 30 or above |
These thresholds come from the Centers for Disease Control and Prevention for adults 20 and older. A result of exactly 25 falls in the overweight category, and exactly 30 falls in the obesity category. The calculator assigns your category using the unrounded value, so a 24.96 that displays as 25.0 still reads healthy weight.
What BMI misses — especially for runners
- BMI screens weight relative to height. It does not measure body fat, lean mass, fat distribution, bone density, fitness, blood pressure, or blood sugar.
- Muscular athletes can carry a high BMI while perfectly healthy, and age-related muscle loss can hide fat gain behind an unchanged number.
- Two runners with the same BMI can have very different health profiles. Treat the number as one input in a bigger conversation, not a verdict.
- Children and teenagers need age- and sex-specific BMI percentiles instead of these adult cutoffs, which this tool does not provide.
Limitations
- This calculator screens; it does not diagnose any condition or decide what action to take.
- Pregnancy, illness, swelling, and limb differences all reduce how representative the number is.
- Use a recent measured height and weight, and retest under similar conditions if you want comparable trends.
Medical note: this page provides general educational information, not individualized medical advice. If you are worried about unexplained weight changes, growth, nutrition, or chronic disease risk, discuss the full picture with a qualified healthcare professional — see our medical disclaimer.
Sources
Related reading
- More Miles Won't Buy More Years: Where the Health Curve Flattens
- Mileage Up, PR Stalled? Audit Your Fueling Before Adding More
- Strength Training for Runners: Two Sessions That Earn Their Place
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