Quick answer: BMI is your weight in kilograms divided by your height in metres squared. At 175 cm and 70 kg: 70 ÷ (1.75 × 1.75) = 22.9, which is in the healthy range of 18.5 to 24.9. For pounds and inches the formula is 703 × lb ÷ in². BMI is a quick screening number for adults – it doesn’t measure body fat directly.
BMI categories for adults
| BMI | WHO category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25 – 29.9 | Overweight |
| 30 – 34.9 | Obesity class I |
| 35 – 39.9 | Obesity class II |
| 40 and above | Obesity class III |
Several Asian health authorities, including guidance used in Pakistan, India and Singapore, use lower cut-offs because health risks rise at lower BMIs in South and East Asian populations: about 23 for overweight and 27.5 for obesity. If that applies to you, read your result with those numbers in mind.
Working it out by hand
Metric: BMI = kg ÷ m². 1.75 m × 1.75 m = 3.0625; 70 ÷ 3.0625 = 22.86.
Imperial: BMI = 703 × lb ÷ in². 5 ft 9 in = 69 in; 69 × 69 = 4,761; 703 × 154 ÷ 4,761 = 22.7.
The healthy weight range for a height is just the formula turned around: 18.5 × m² to 24.9 × m². At 175 cm that is about 56.7 to 76.3 kg.
What BMI can’t tell you
- Muscle vs. fat – a rugby player can have a BMI of 29 with little body fat.
- Where fat sits – fat around the waist carries more risk. A waist under half your height is a useful second check.
- Children and teenagers – they need age- and sex-specific percentile charts, not adult categories.
- Pregnancy and older age – the adult ranges don’t apply in the same way.
Use BMI as a starting point for a conversation with your doctor, not as a diagnosis.
BMI tells you where you are; the calorie calculator tells you how much to eat to stay there or move toward a healthy weight. To track progress over weeks, the percentage calculator shows your change as a percentage.
How to calculate your BMI
- Choose your units. Metric for centimetres and kilograms, imperial for feet, inches and pounds.
- Enter height and weight. Use your weight without heavy clothes or shoes for the most accurate number.
- Read your category. The marker on the colour bar shows where your BMI sits between the categories.
- See your healthy range. The result shows the weight range that gives a BMI of 18.5–24.9 at your height.
Worked example in pounds and inches
Height 5 ft 4 in, weight 150 lb.
- Height in inches: 5 × 12 + 4 = 64 in. Squared: 64 × 64 = 4,096.
- BMI = 703 × 150 ÷ 4,096 = 25.7 – just into the overweight range.
- Healthy range at 64 in: 18.5 × 4,096 ÷ 703 = 107.8 lb to 24.9 × 4,096 ÷ 703 = 145.1 lb.
So this person is about 5 lb above the top of the healthy range – a small difference that waist size and fitness may matter more for than the BMI number itself.
Measuring correctly
- Weigh in the morning, after the bathroom and before eating, in light clothes.
- Measure height without shoes, back against a wall, looking straight ahead.
- Track the trend over weeks; day-to-day changes of 1–2 kg are mostly water.
Frequently asked questions
What is a healthy BMI?
For adults, the World Health Organization classes 18.5 to 24.9 as a healthy weight. Some Asian guidelines use 23 as the start of overweight.
How is BMI calculated?
Weight in kilograms divided by height in metres squared. In pounds and inches: 703 × weight ÷ height².
Is BMI accurate for athletes?
Not very. Muscle weighs more than fat, so muscular people can show as overweight while having little body fat.
Can children use this BMI calculator?
No. Children and teenagers need BMI-for-age percentiles from growth charts; adult categories do not apply.
What weight should I be for my height?
The calculator shows the range that keeps your BMI between 18.5 and 24.9. Your doctor may suggest a narrower target for you.
Does BMI differ for men and women?
The formula and adult categories are the same, although women naturally carry more body fat at the same BMI.
Is a BMI of 25 bad?
It is the boundary between healthy weight and overweight. On its own it is not a diagnosis; waist size, activity, blood pressure and blood tests give a fuller picture.
How do I lower my BMI?
Only by changing weight (height is fixed). Gradual loss of 0.25–0.5 kg a week through food and activity changes is generally considered safe for adults.