BMI Calculator: Body Mass Index and Ideal Weight
BMI, the body mass index, is the simplest number for judging whether your weight matches your height. It takes seconds to work out, doctors use it worldwide, and it is reliable enough to tell you whether it is time to talk to a doctor. The calculator below gives your BMI, the category it falls into and the healthy weight range for your height. If you also enter your waist circumference, you get an assessment that is often more important than BMI itself. Below is an explanation of when the number misleads and when a hormone, not the plate, is behind the kilograms.
BMI calculator
Valid for adults aged 18 to 65. Not valid in pregnancy or for athletes with a large muscle mass.
How BMI is calculated
The formula is the same for women and men: weight in kilograms divided by height in metres squared. For a person 170 cm tall weighing 68 kg the calculation is 68 / (1.7 × 1.7) = 23.5. The result is then placed in the World Health Organization categories, which are the same all over the world and do not depend on age or sex.
| BMI | Category | What it means in practice |
|---|---|---|
| below 18.5 | Underweight | Check food intake, thyroid, digestion and any chronic illness. |
| 18.5 to 24.9 | Normal weight | Lowest risk of weight-related disease. |
| 25.0 to 29.9 | Overweight | Risk rises, especially if waist circumference is also increased. |
| 30.0 to 34.9 | Class I obesity | An examination, tests and a plan with a doctor are recommended. |
| 35.0 to 39.9 | Class II obesity | High risk of diabetes, hypertension and heart disease. |
| 40 and above | Class III obesity | Treatment under medical supervision is needed. |
Ideal weight by height
There is no single ideal weight. For every height there is a range in which BMI falls between 18.5 and 24.9, and any weight in that range is healthy. The table gives that range for the most common heights, and the calculator works it out exactly for yours.
| Height | Healthy weight | Overweight from | Obesity from |
|---|---|---|---|
| 155 cm | 44.5 to 59.8 kg | 60.1 kg | 72.1 kg |
| 160 cm | 47.4 to 63.7 kg | 64.0 kg | 76.8 kg |
| 165 cm | 50.4 to 67.8 kg | 68.1 kg | 81.7 kg |
| 170 cm | 53.5 to 72.0 kg | 72.3 kg | 86.7 kg |
| 175 cm | 56.7 to 76.3 kg | 76.6 kg | 91.9 kg |
| 180 cm | 59.9 to 80.7 kg | 81.0 kg | 97.2 kg |
| 185 cm | 63.3 to 85.2 kg | 85.6 kg | 102.7 kg |
| 190 cm | 66.8 to 89.9 kg | 90.3 kg | 108.3 kg |
When BMI misleads
BMI cannot tell muscle from fat. Someone who lifts weights can have a BMI of 27 with very little body fat, while someone with a BMI of 23 can carry too much fat around the organs and have every metabolic problem of obesity. That is why BMI is read together with waist circumference and, where needed, a body composition analysis.
- Athletes and physically active people. Muscle mass raises BMI without any health risk.
- People over 65. Muscle is lost with age, so the same BMI means more fat. In older adults a BMI up to 27 is generally not considered a problem, while being underweight is more dangerous than in younger people.
- Pregnancy and breastfeeding. BMI is not interpreted; weight gain is tracked by week of pregnancy instead.
- Children and adolescents. Percentile charts for age and sex are used; the adult table does not apply.
- Swelling and fluid retention. In heart, kidney or thyroid disease, weight can be water rather than fat.
Waist circumference says more than the scale
Fat around the waist, the kind that builds up between the organs in the abdomen, is the most metabolically active and contributes most to insulin resistance, high blood pressure and fatty liver. That is why waist circumference predicts risk better than BMI. It is measured standing, halfway between the lowest rib and the top of the hip bone, after a normal breath out, without pulling the stomach in.
| Increased risk | Substantially increased risk | |
|---|---|---|
| Women | 80 cm and above | 88 cm and above |
| Men | 94 cm and above | 102 cm and above |
When a hormone is behind the kilograms
In most people excess weight comes down to the balance between intake and expenditure. But in some patients diet and exercise give no result because the body is working against them. The most common reasons are an underactive thyroid, insulin resistance, polycystic ovary syndrome, the changes of menopause, raised cortisol and certain medicines. Signs that point this way are sudden weight gain without any change in habits, weight that gathers only around the waist, constant tiredness, sugar cravings, irregular cycles and the inability to lose a single kilogram despite discipline.
In those situations tests come before any new diet: TSH and FT4 for the thyroid, fasting glucose and insulin from which the HOMA index is calculated, a lipid profile and, if needed, sex hormones. Based on the results an endocrinologist can say whether there is a hormonal cause and how it is treated, and only then does a nutrition plan make sense. We have also written about how hormones affect weight in how hormones affect weight and metabolism.
Prices
| Service | Price |
|---|---|
| Endocrinologist consultation | from 7,000 RSD |
| Endocrinology consultation with thyroid ultrasound | from 12,000 RSD |
| General practitioner consultation | 4,000 RSD |
Frequently asked questions
What is a normal BMI?
For adults a normal BMI is 18.5 to 24.9. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 and above is obesity. The thresholds are the same for women and men.
How is BMI calculated?
Weight in kilograms divided by height in metres squared. Example: 80 kg and 180 cm give 80 / (1.8 × 1.8) = 24.7.
Is BMI the same for women and men?
The formula and the categories are the same. The difference is in waist circumference: the threshold for increased risk is 80 cm in women and 94 cm in men, because fat is distributed differently between the sexes.
Is BMI reliable for athletes?
No. Muscle is heavier than fat, so a well-muscled person easily passes a BMI of 25 without a single excess kilogram. In athletes body composition and waist circumference are assessed, not BMI.
My BMI is high but I eat little. What should I do?
Check your hormones before another diet. An underactive thyroid and insulin resistance are the two most common reasons weight does not respond to eating less, and both are detected with simple blood tests and can be treated. An endocrinologist consultation with TSH, fasting glucose and fasting insulin is the first step.
Book an appointment
If your BMI is above 25, your waist is above the threshold, or your weight does not respond to a change in habits, book an endocrinologist consultation at Miren Medic. Hormone tests, thyroid ultrasound and a treatment plan are all done in one place, without a referral.
