BMI calculator

Metric BMI is weight in kg ÷ (height in metres)². If you've seen the imperial version — 703 × pounds ÷ inches² — it's the same ratio, just rearranged for different units.

1. Start with your weight: 70 kg.
2. Convert height to metres: 170 cm → 1.70 m.
3. Square it: 1.70 × 1.70 ≈ 2.890.
4. Divide: 70 ÷ 2.890 ≈ 24.2.
5. That lands you in the normal weight band — read the next section before drawing any conclusions from it.

At 170 cm that puts the general "normal" range at roughly 53.5-72 kg. Go by the South Asian thresholds instead and "overweight" starts closer to 66.5 kg, "obesity" closer to 72.3 kg. Neither column is more "official" than the other — they come from different research bases for different population groups, which is exactly why it's worth knowing both.

Same height, different weight

Same weight, different height

Height is squared in the formula, so it swings BMI harder than the equivalent percentage change in weight does. It's also why a rushed or inaccurate height measurement — common with wall-chart estimates — quietly throws off every BMI calculated from it afterward.

BMI was built to describe populations, not individual bodies, and it shows in a few predictable ways:

• Muscular people. Athletes and anyone who trains seriously can read "overweight" or higher with very low body fat, simply because muscle is denser than fat and the formula can't tell them apart.
• Older adults. A "normal" BMI in someone over roughly 65 can sometimes hide muscle loss (sarcopenia) rather than reflect good health — some research even suggests a slightly higher BMI may be protective at that age.
• Where the fat sits. Two people with an identical BMI can carry very different risk if one stores more fat around the abdomen — waist circumference catches this, BMI doesn't.
• Children, teenagers, and pregnancy. None of these bands apply. Children need percentile growth charts; pregnancy has its own trimester-specific weight-gain guidance from an obstetrician.

Flip the formula around — weight = target BMI × height² — and you get a concrete weight goal instead of an abstract number. At 170 cm:

Read these as reference points, not a prescription — your frame, muscle mass, and age all belong in that decision, and a calculator can't see any of them. If weight loss is the goal, roughly 0.5-1% of body weight a week tends to hold onto muscle better than a crash approach.

• Weigh yourself at a consistent time — first thing in the morning, before eating, is the least noisy.
• Use the same scale on a hard, flat surface each time; carpet throws off calibration on some models.
• Measure height without shoes, heels and shoulders against a wall, looking straight ahead.
• Re-measure height every couple of years — adults' height drifts slightly, and an old figure quietly skews every BMI calculated from it.
• Note the date with each reading, so a few months from now you can tell a real trend from normal day-to-day noise.

• Reacting to one reading. Weight moves with hydration and food intake alone — judge a trend over weeks, not a single number.
• Mixing units. Feet-and-inches typed into a centimetre field produces a BMI that's wrong by a wide margin — double check the unit before trusting the result.
• Using adult bands for a child. Anyone under 18 needs a paediatric percentile chart instead.
• Stopping at BMI alone. Pair it with a waist measurement or body fat estimate before drawing any real conclusion.
• Chasing a fast number change. Rapid weight loss usually costs more muscle than a steady, guided pace does.

This is the one place where BMI's general limitations turn into something worth acting on: Indian and other South Asian cohorts have repeatedly shown higher diabetes and cardiovascular risk at BMI numbers the general WHO scale would still file under "normal." The leading explanation is a tendency toward more abdominal fat at a given body weight compared with European populations, which is why the lower 23/25 thresholds in the table above exist and why routine waist measurement is common alongside BMI in Indian clinical practice. If your BMI sits in the high-20 to low-30 range on the general scale, it's worth checking where you land on the South Asian columns too, rather than assuming "normal" clears you.

Three cheap, common screening numbers, each catching something the others miss:

Run BMI alongside waist circumference and you already have a noticeably fuller picture than either one gives alone. Try the body fat calculator next to this page, and the calorie calculator if you're actually trying to shift the number.

A BMI of 24.2 at 70 kg and 170 cm puts you in the normal weight band — a decent starting signal, not a diagnosis. Check it against waist size and how you actually feel, take the South Asian thresholds seriously if you're close to the general "normal" line, and bring a doctor or dietitian into the conversation if you have a specific health condition, train heavily, are pregnant, or are checking a child rather than yourself.

Figures above are computed live from the weight and height you entered (or the illustrative defaults shown) using the standard metric BMI formula. Category bands reflect commonly cited WHO adult cut-offs alongside the lower thresholds used for South Asian populations. The reverse-calculation weights simply invert the same formula. Nothing here is medical advice.