How BMI is calculated
BMI = weight in kilograms ÷ height in metres squared. Illustrative example: 78 kg and 165 cm (1.65 m). Height squared is 1.65 × 1.65 = 2.7225, so BMI = 78 ÷ 2.7225 = 28.7, in the overweight band. If you enter feet, inches and pounds, the calculator converts to cm and kg first (1 inch = 2.54 cm, 1 lb = 0.4536 kg).
The categories
- Below 18.5: underweight.
- 18.5 to under 25: healthy weight.
- 25 to under 30: overweight.
- 30 or more: obesity, split into class 1 (30 to under 35), class 2 (35 to under 40) and class 3 (40 or more).
Your healthy weight range and how far you are from it
There is no single ideal weight, only a range. The calculator multiplies your height squared by 18.5 and by 24.9. For 165 cm: 2.7225 × 18.5 = 50.4 kg and 2.7225 × 24.9 = 67.8 kg, so the range is 50.4 to 67.8 kg. At 78 kg you are about 10.2 kg above the upper end.
The limits of BMI
- BMI is a screening measure and does not diagnose anything on its own. It cannot tell muscle from fat, so a muscular athlete can be classed as overweight with little body fat. It also says nothing about where fat is carried, which is why waist circumference is used too.
- A WHO expert consultation (2004) proposed public health action points of 23 and 27.5 for Asian populations, because risk can rise at a lower BMI. The NHS uses 23 and 27.5 for South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds. These sources give no thresholds specific to Egyptians, so ask your doctor.
- The calculator does not apply in pregnancy or under 18. Children are assessed on growth charts.
Common mistakes
- Typing the height in metres in the cm box (1.65 instead of 165).
- Mixing up pounds and kilograms.
- Judging health from one number.
One number is not the whole picture. In MyClinic (Sehaty) the patient’s medical file holds their history and prescriptions are issued to it electronically, and the health passport carries a QR code for emergencies and a summary of health data, so your doctor can read your weight alongside the rest.
Read about the digital health passport · See MyClinic · Request a demo
Sources
- CDC: adult BMI categories (18.5, 25, 30 and obesity classes)
- WHO: obesity and overweight fact sheet (BMI definition; children use growth references)
- NHS: overweight and obesity (muscle; thresholds of 23 and 27.5 for some backgrounds)
- WHO Expert Consultation, Lancet 2004;363:157-63 (action points 23 and 27.5 for Asian populations)
Questions
How do I calculate BMI?
Divide your weight in kilograms by your height in metres squared. 78 kg at 1.65 m: 78 ÷ 2.7225 = 28.7.
What is a normal BMI?
18.5 to under 25 is a healthy weight. Below is underweight, 25 and above is overweight and 30 and above is obesity.
How do I find my ideal weight for my height?
There is no single number, only a healthy range. The calculator works it out from BMI 18.5 to 24.9 and shows how far you are from it.
Is BMI accurate for athletes?
Not always. BMI cannot tell muscle from fat, so a muscular athlete can be classed as overweight. Ask your doctor.
Can children or pregnant women use it?
No. It is for adults aged 18 and over; children are assessed on growth charts by age and sex. It does not apply in pregnancy, so ask your doctor or midwife.
Do you store my height and weight?
No. The calculation runs in your browser and nothing is sent to a server. To return to it, copy the link to your calculation.
Read the guide
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