What Is My BMI and Ideal Weight Range?
I built a free BMI Calculator that follows WHO standards, returns your ideal weight band and BMR, with WHO classification tables and FAQ.
Quick Answer
Enter your gender, age, height and weight in the calculator below to get your Body Mass Index instantly.
Your BMI is classified against WHO standards (Underweight, Normal, Overweight, Obese) and the tool also returns your ideal weight range and resting metabolic rate.
BMI is a fast screening number, not a verdict. Pair it with waist size, body fat and metabolic markers for a fuller picture.
What is Body Mass Index?
BMI is a simple weight-to-height ratio (kg divided by height in metres squared) used by the WHO and clinicians worldwide to screen for weight-related health risk.
It is not a direct measure of body fat, but a high BMI is strongly linked to Type 2 Diabetes, hypertension and cardiovascular disease across large populations.
BMI categories chart (adults 20+)
| BMI Score (kg/m²) | Classification | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Malnutrition, osteoporosis |
| 18.5-24.9 | Healthy Weight | Lowest risk |
| 25.0-29.9 | Overweight | Increased |
| 30.0-34.9 | Obesity (Class I) | High |
| 35.0-39.9 | Obesity (Class II) | Very high |
| 40.0 and above | Obesity (Class III) | Extremely high |
How to calculate BMI
The formula is the same for men and women:
- Metric: weight (kg) ÷ height² (m)
- Imperial: [weight (lbs) ÷ height² (in)] × 703
Example: a person who is 170 cm and 70 kg has a BMI of 70 ÷ (1.70 × 1.70) = 24.2, which sits in the Healthy band.
Is BMI accurate for everyone?
No. BMI is a screening tool and ignores muscle mass, bone density and fat distribution.
- Athletes: Often score Overweight because muscle is denser than fat.
- Elderly: May score Healthy while carrying low muscle (sarcopenia).
- Asian populations: Health risks rise at lower BMI scores, with Overweight starting closer to 23.
BMI cut-offs by population
| Group | Healthy upper limit | Overweight starts |
|---|---|---|
| General WHO | 24.9 | 25.0 |
| Asian populations | 22.9 | 23.0 |
| Adults 65+ | ~27 | 27.0 |
What counts as a healthy weight?
A healthy weight is more than a number on the scale. It also includes:
- Waist size: under 40 inches for men, under 35 inches for women.
- Blood pressure: in the normal range, around 120/80.
- Metabolic markers: normal blood sugar and cholesterol.
If your BMI sits high but those markers are clean, weight loss may be less urgent than the number suggests.
Frequently asked questions
How do I calculate my BMI?
Use the formula weight (kg) ÷ height (m)². The calculator above handles the conversions for you, including imperial units.
What is the BMI of someone 70 kg and 170 cm?
1.70 × 1.70 = 2.89, then 70 ÷ 2.89 = 24.2. That falls into the Healthy Weight band.
How accurate is BMI as a health measure?
It is a useful population screen but a blunt tool individually. It cannot distinguish bone, muscle and fat, so it can misclassify athletes and the elderly.
Is the calculator different for men and women?
The math is identical. Women naturally carry more body fat at the same BMI score. If you are pregnant, use a pregnancy weight tracker instead.
How does age affect BMI?
For adults over 65, a slightly higher BMI (around 25 to 27) is often protective against frailty. Children need a BMI Percentile chart, not the adult formula.
Does ethnicity affect my result?
Yes. New guidelines suggest a BMI of 23 or higher may already be Overweight for Asian populations, compared to 25 for the general WHO standard.
Why is my BMI high but I'm not fat?
Muscle is denser than fat. If you train heavily and have visible definition, lean on body fat percentage and waist measurements rather than BMI.
Can I have a normal BMI but a fat belly?
Yes. This is called skinny fat: healthy weight, but high visceral fat. If your waist is over 40 inches (men) or 35 inches (women), risk is elevated regardless of BMI.
What is an alarming BMI score?
A BMI over 30 raises heart disease and diabetes risk significantly. Over 40 (Class III) usually warrants medical support. Under 18.5 is also concerning due to malnutrition risk.
How can I lower my BMI naturally?
Hold a moderate calorie deficit (around 500 kcal a day), aim for about 0.5 kg of loss per week, and walk daily. Strength training preserves the muscle you want to keep.
How often should I check my BMI?
Once a month is enough. Daily weighing is noisy because of water retention. Track the long-term trend across three to six months.
Formula and methodology
The calculator uses the WHO standard formula and classification bands.
- Metric: BMI = weight (kg) ÷ height² (m)
- Imperial: BMI = [weight (lb) ÷ height² (in)] × 703
- Ideal weight: reverses the formula to find the kg range that places your height between 18.5 and 24.9.
- BMR: Mifflin-St Jeor equation, sex-specific.
Complete your analysis
Once you know your BMI, build the rest of the picture with these tools:
- Calorie Calculator for daily intake at maintenance or in a deficit.
- Macro Split Calculator for protein, carbs and fat targets.
- BMR and TDEE Calculator for energy burn across activity levels.
- Body Fat Calculator for a richer composition reading than BMI alone.
Medical disclaimer
This calculator and article are for general educational and wellness purposes only. They are not a substitute for professional medical advice, diagnosis or treatment. Results are estimates based on population formulas and do not account for every individual factor.
If you are pregnant or breastfeeding, under 18, over 65, an athlete, recovering from illness or surgery, or living with a chronic condition (diabetes, heart, kidney, thyroid, eating disorder), speak to a qualified healthcare professional before changing your diet, exercise or hydration habits based on these numbers.
See the full site-wide Disclaimer & Notice for the complete terms that apply to every calculator and tool on dmbio.