BMI Calculator
Check your Body Mass Index in seconds — metric or imperial — and see what your number means for your health.
Calculate
Your height in centimeters — 175 cm is about 5′9″.
Your weight in kilograms, ideally measured in the morning.
Your total height in inches — 5′9″ is 69 inches.
Your weight in pounds, ideally measured in the morning.
The BMI Formula Explained
BMI estimates whether your weight is in a healthy range for your height. The formula is simple:
In imperial units: BMI = 703 × weight (lb) ÷ height (in)2. The 703 is just a conversion constant so the same cutoffs work in both systems.
For example, at 70 kg and 1.75 m: BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9 — comfortably in the normal range.
BMI Categories (CDC / WHO)
| BMI | Category | What it means |
|---|---|---|
| Below 18.5 | Underweight | May indicate undernutrition or an underlying condition — worth discussing with a doctor. |
| 18.5 – 24.9 | Normal weight | Associated with the lowest health risks for most adults. |
| 25 – 29.9 | Overweight | Above the healthy range; modest weight loss often improves blood pressure and blood sugar. |
| 30 and above | Obese | Linked to higher risk of heart disease, diabetes, and joint problems — a clinician can help plan next steps. |
What BMI Doesn't Tell You
BMI is a screening tool, not a diagnosis. It can't tell muscle from fat — a muscular athlete can land in "overweight" while being very fit, and it says nothing about where fat sits (belly fat carries more risk than fat elsewhere). It also wasn't designed for children, pregnant people, or adults over 65, where the cutoffs shift.
Use it as a starting point: if your BMI is outside the normal range, pair it with a waist measurement and a conversation with your doctor rather than a crash diet. Small, sustained changes beat dramatic ones — the research is unambiguous on that.
Worked Example: Finding a Healthy Weight Range
The setup
You're 1.75 m tall and want to know what weight range counts as healthy.
Step 1 — Lower bound (BMI 18.5)
18.5 × 1.752 = 18.5 × 3.0625 = 56.7 kg.
Step 2 — Upper bound (BMI 24.9)
24.9 × 1.752 = 24.9 × 3.0625 = 76.3 kg.
Result
At 1.75 m, the healthy range is roughly 56.7–76.3 kg (125–168 lb). Enter your own height above to see your personal range.
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Frequently Asked Questions
How is BMI calculated?
BMI = weight (kg) ÷ height (m)². In imperial units: BMI = 703 × weight (lb) ÷ height (in)². For example, 70 kg at 1.75 m gives 70 ÷ 3.0625 = 22.9.
What are the BMI categories?
Underweight is below 18.5, normal weight is 18.5–24.9, overweight is 25–29.9, and obese is 30 or above. These CDC/WHO cutoffs apply to most adults.
Is BMI accurate?
BMI is a useful screening tool but not a diagnosis. It cannot tell muscle from fat, so muscular athletes can score as "overweight" while being fit. It also was not designed for children, pregnant people, or older adults.
What is a healthy BMI?
18.5 to 24.9 is associated with the lowest health risks for most adults. The calculator above also shows the exact healthy weight range in kg or lb for your height.
How much weight should I lose to reach a normal BMI?
Enter your height above and look at the healthy range row — the top of that range is your target ceiling. Even a 5–10% reduction from your current weight can meaningfully improve blood pressure and blood sugar.
Does BMI work for athletes?
Not well — muscle is denser than fat, so very muscular people often land in "overweight" or "obese" despite low body fat. Athletes should rely on body-fat percentage and waist measurements instead.