Quick Answer
BMI (body mass index) is your weight in kilograms divided by the square of your height in metres. For 70 kg and 1.70 m: 70 ÷ (1.70 × 1.70) = 24.2. Under WHO cut-offs, 18.5–24.9 is a healthy range, 25–29.9 is overweight and 30 or more is obese. For South Asians, many doctors use lower cut-offs — overweight from 23 and obese from 25. BMI is a screening tool, not a diagnosis.
What is a BMI Calculator?
A BMI Calculator (BMI कैलकुलेटर) works out your body mass index — a number that compares your weight with your height. BMI is used worldwide by doctors, health agencies and fitness professionals as a quick first check of whether an adult's weight is in a healthy range for their height. It is simple: weight in kilograms divided by height in metres squared.
This calculator accepts metric or US units, shows your category under either the WHO international cut-offs or the lower cut-offs widely used for Asian and Indian adults, and goes further than a single number: it shows the healthy weight range for your height, how many kilograms or pounds you would need to gain or lose to reach it, your BMI Prime and a colour scale. Remember that BMI is a screening tool, not a diagnosis — it should be read together with other measures and, where needed, a doctor's advice.
Key Features
- Metric and US units — kg and cm, or pounds plus feet and inches, converted exactly.
- Two sets of cut-offs — WHO international, or Asian/Indian (overweight from 23, obese from 25).
- Healthy weight range for your exact height.
- Gap to healthy — how much to gain or lose to reach the range.
- Obesity class (I, II, III) under WHO cut-offs.
- BMI Prime and a visual colour scale.
- Private — nothing leaves your device.
How to Check Your BMI — Step by Step
- Choose units: Metric (kg, cm) or US (lb, ft-in). Switching carries your values across.
- Enter your weight and height. Measure height without shoes and weight in light clothing, ideally in the morning.
- Choose the cut-offs. Use Asian/Indian if you are of South Asian origin, or WHO international otherwise.
- Read your BMI and category, then check the healthy range and the gap below.
The BMI Formula with Examples
Metric: BMI = weight (kg) ÷ height (m)²
Example: 70 kg and 170 cm → 70 ÷ (1.70 × 1.70) = 70 ÷ 2.89 = 24.2. Under WHO cut-offs this is in the normal range; under Asian/Indian cut-offs (overweight from 23) it is in the overweight range — which shows why the choice of cut-offs matters.
US units: BMI = 703 × weight (lb) ÷ height (in)²
Example: 154 lb and 5 ft 7 in (67 inches) → 703 × 154 ÷ 4,489 = 24.1. The calculator converts pounds and inches to kilograms and metres using the exact international definitions, so both methods agree.
Healthy weight range: rearrange the formula — weight = BMI × height². For 1.70 m: 18.5 × 2.89 = 53.5 kg and 24.9 × 2.89 ≈ 72 kg (the calculator uses 25 as the boundary: 25 × 2.89 = 72.25, shown as 72.3 kg). With Asian/Indian cut-offs the upper limit is 23 × 2.89 = 66.5 kg.
BMI Categories
| Category | WHO international | Asian / Indian (commonly used) |
|---|---|---|
| Underweight | Below 18.5 | Below 18.5 |
| Normal weight | 18.5 – 24.9 | 18.5 – 22.9 |
| Overweight | 25 – 29.9 | 23 – 24.9 |
| Obese | 30 and above (class I 30–34.9, II 35–39.9, III 40+) | 25 and above |
The lower Asian cut-offs reflect research showing that South Asian adults tend to have a higher percentage of body fat and a higher risk of type 2 diabetes, high blood pressure and heart disease at the same BMI as Europeans. Indian clinical consensus guidelines published in 2009 recommended these lower thresholds, and many Indian doctors use them. Some guidelines also use 18.0 rather than 18.5 as the lower limit of normal.
Healthy Weight Range by Height (WHO 18.5–24.9)
| Height | Healthy weight (WHO) | Upper limit (Asian, BMI 23) |
|---|---|---|
| 150 cm (4 ft 11 in) | 41.6 – 56.0 kg | 51.8 kg |
| 155 cm (5 ft 1 in) | 44.4 – 59.8 kg | 55.3 kg |
| 160 cm (5 ft 3 in) | 47.4 – 63.7 kg | 58.9 kg |
| 165 cm (5 ft 5 in) | 50.4 – 67.8 kg | 62.6 kg |
| 170 cm (5 ft 7 in) | 53.5 – 72.0 kg | 66.5 kg |
| 175 cm (5 ft 9 in) | 56.7 – 76.3 kg | 70.4 kg |
| 180 cm (5 ft 11 in) | 59.9 – 80.7 kg | 74.5 kg |
| 185 cm (6 ft 1 in) | 63.3 – 85.2 kg | 78.7 kg |
Limitations of BMI
- Muscle vs fat: BMI cannot tell them apart. Athletes and bodybuilders may be classed as overweight while having low body fat.
- Fat distribution: fat around the waist carries more risk than fat on the hips; BMI ignores where fat is.
- Age and sex: older adults tend to have more fat at the same BMI, and women naturally carry more fat than men.
- Children and teens: need age- and sex-specific percentile charts instead.
- Pregnancy: BMI does not apply during pregnancy.
That is why doctors combine BMI with waist circumference, waist-to-height ratio (a common guide is keeping your waist below half your height), blood pressure, blood sugar and cholesterol before drawing conclusions.
What to Do With Your Result
- Underweight: it can reflect low food intake, high activity or a medical issue. Speak to a doctor if it is unexplained or you have lost weight without trying.
- Normal: keep up regular physical activity and a balanced diet; check your waist measurement too.
- Overweight: modest changes — more daily movement, fewer sugary drinks and refined snacks, better sleep — often help. Our Calorie Calculator estimates your daily needs.
- Obese: a doctor can check for related conditions and suggest a safe plan. Even a 5–10% weight loss can bring health benefits.
How to Measure Accurately at Home
- Height: stand barefoot with your heels, back and head against a wall, look straight ahead, and place a flat object such as a book on your head at a right angle to the wall. Mark the wall under it and measure from the floor to the mark.
- Weight: use a digital scale on a hard, flat floor (not carpet). Weigh yourself in the morning after using the toilet and before eating, wearing light clothing.
- Waist: breathe out normally and measure around your belly at the level of the navel, keeping the tape snug but not tight.
- Consistency: use the same scale, time of day and clothing each time so you can compare readings over months.
Who Finds This Useful?
- Adults checking whether their weight is in a healthy range for their height.
- People starting a fitness or weight-management plan who want a baseline.
- Gym trainers and dietitians doing a quick first screening.
- Insurance or job medical forms that ask for BMI.
- South Asian users who want the lower, more relevant cut-offs.
Common Mistakes to Avoid
- Entering height in feet as centimetres — 5.7 is not 5 ft 7 in; use the US tab for feet and inches.
- Measuring with shoes or heavy clothing — this skews both numbers.
- Using adult categories for children — they need percentile charts.
- Treating BMI as a diagnosis — it is a screening number only.
- Checking daily — normal day-to-day weight changes make daily BMI noisy.
Quick Glossary
- BMI: body mass index, kg ÷ m².
- BMI Prime: BMI ÷ 25; above 1.0 means above the WHO normal upper limit.
- Cut-off: the BMI value at which a category starts.
- Waist-to-height ratio: waist ÷ height; a value under 0.5 is a commonly used healthy guide.
- Waist circumference: measured around the belly at the level of the navel; indicates abdominal fat.
- Obesity class: WHO subdivisions I (30–34.9), II (35–39.9) and III (40+).
Why Use This BMI Calculator?
It supports both metric and US units, offers the Asian/Indian cut-offs that many calculators leave out, shows a personalised healthy weight range and gap, and explains clearly what BMI can and cannot tell you. It is free, fast and private. This tool is for general information and is not medical advice — consult a qualified doctor about your health.
BMI Calculator — Key Facts
| Formula | BMI = weight (kg) ÷ height (m)² |
|---|---|
| WHO categories | < 18.5 underweight · 18.5–24.9 normal · 25–29.9 overweight · ≥ 30 obese |
| Asian / Indian cut-offs | Overweight from 23, obese from 25 |
| Units | kg and cm, or lb and feet + inches (converted exactly) |
| Extras | Healthy weight range, gap to healthy range, BMI Prime, colour scale |
| For | Adults aged 20+; not for children, pregnancy or as a diagnosis |
Frequently Asked Questions
How is BMI calculated?
BMI = weight in kilograms ÷ (height in metres)². For 70 kg and 170 cm: 70 ÷ (1.7 × 1.7) = 70 ÷ 2.89 = 24.2. In US units, BMI = 703 × pounds ÷ inches², which gives the same result.
What is a healthy BMI?
For adults, the WHO considers 18.5 to 24.9 a normal range. For people of South Asian origin, many Indian guidelines use a lower upper limit of about 22.9, because health risks rise at lower BMI levels.
Why are the Asian / Indian cut-offs lower?
Studies show that many South Asians have more body fat and a higher risk of diabetes and heart disease at the same BMI than Europeans. Indian consensus guidelines therefore treat a BMI of 23 or more as overweight and 25 or more as obese.
What does BMI not measure?
BMI does not distinguish muscle from fat, does not show where fat is stored, and does not account for age, sex or ethnicity beyond the cut-offs you choose. A muscular athlete can have a high BMI while being very fit.
Is this BMI calculator suitable for children?
No. For children and teenagers, BMI must be compared with age- and sex-specific growth charts (percentiles). Use a paediatric BMI tool or ask a doctor.
Can I use BMI during pregnancy?
Not reliably — weight gain in pregnancy is expected. Doctors use pre-pregnancy BMI to guide healthy weight gain, so ask your doctor or midwife.
What is the healthy weight range for my height?
The calculator shows it below your result: it is the weight that gives a BMI from 18.5 to 24.9 (WHO) or 18.5 to 22.9 (Asian/Indian) at your height. For 170 cm, the WHO range is about 53.5 to 72.3 kg.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the upper limit of the WHO normal range. A value below 1.0 means you are under that limit; 1.2 means your BMI is 20% above it.
Does waist size matter as well as BMI?
Yes. Waist circumference shows abdominal fat, which is linked to health risk. Commonly used Indian thresholds are about 90 cm for men and 80 cm for women; a doctor can interpret it with your BMI.
How often should I check my BMI?
Monthly is plenty for most adults. Weight naturally varies from day to day, so measure at the same time of day, ideally in the morning.
Is my data stored?
No. The calculation runs in your browser and nothing is sent to a server.
Is the BMI Calculator free?
Yes. It is free with no sign-up and works on any device. It is for information only and is not medical advice.
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