BMI Calculator
A BMI number on its own says little — what matters is where it sits and what weight range it maps to for your height. This calculator works out your BMI from height and weight in metric or imperial units, places it in the standard or Asian-cutoff band, and converts that band into a healthy weight range for your exact height, plus how much to lose or gain to reach it and your BMI prime. Every figure shows its math, example values are labelled as examples, and all results are estimates only — not medical advice.
Switching units only changes how you enter height and weight — the BMI formula is the same either way.
Your height in centimetres. 1.75 m is 175 cm.
Your weight in kilograms.
Asian cutoffs use a lower healthy ceiling (22.9 instead of 24.9) because health risks rise at lower BMIs in Asian populations. The toggle changes the band, never the BMI itself.
Your BMI — Healthy
22.9
- BMI70.0 kg ÷ 1.75 m².
- 22.9
- Healthy weight range (low)18.5 × 1.75 m² = 56.7 kg.
- 56.7kg
- Healthy weight range (high)24.9 × 1.75 m² = 76.3 kg.
- 76.3kg
- Distance from the healthy rangeAlready inside the healthy range (56.7–76.3 kg).
- 0kg
- BMI prime22.9 ÷ 25. Below 1 sits inside the standard healthy band's top edge; above 1 sits above it.
- 0.91
How it was calculated
- Height: 175 cm = 1.75 m. Weight: 70.0 kg = 70.0 kg.
- BMI: 70.0 ÷ 1.75² = 22.9.
- Category: Healthy (Standard bands: healthy 18.5–24.9, overweight 25–29.9, obese 30+.)
- Healthy range for this height: 18.5 × 1.75² = 56.7 kg to 24.9 × 1.75² = 76.3 kg.
- You are already inside the healthy range, so there is nothing to lose or gain to reach it.
- BMI prime: 22.9 ÷ 25 = 0.91.
- Estimates only — not medical advice. BMI is a screening number, not a diagnosis: it does not measure body fat, muscle, or health on its own.
How it works
BMI = weight in kilograms ÷ height in metres squared. The worked example is 70 kg at 1.75 m: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9, which sits in the healthy band. Imperial inputs convert first — 5 feet 10 inches is 70 inches × 0.0254 = 1.78 m, and 170 lb × 0.45359237 = 77.1 kg, giving 77.1 ÷ (1.78 × 1.78) = 24.4, also healthy.
The healthy weight range is the healthy band multiplied by height squared: at 1.75 m the standard range is 18.5 × 3.0625 = 56.7 kg to 24.9 × 3.0625 = 76.3 kg. With Asian cutoffs the same height tops out at 22.9 × 3.0625 = 70.1 kg — the BMI is identical, only the band changes. Weight to lose or gain is simply your weight minus the nearest end of that range.
BMI prime is BMI ÷ 25: the brief example gives 22.9 ÷ 25 = 0.91, and the imperial example gives 24.4 ÷ 25 = 0.98. A prime below 1 sits inside the standard healthy band's top edge; a prime of 1.20 means a BMI of 30, the obese threshold. Prime is a compact way to say how far above or below the healthy ceiling a BMI sits.
Worked examples
Metric example: 70 kg at 1.75 m → BMI 22.9, healthy
Enter 175 cm and 70 kg: BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9, in the healthy band (18.5–24.9). The healthy range for this height is 56.7–76.3 kg, so there is nothing to lose or gain to reach it, and BMI prime is 22.9 ÷ 25 = 0.91. Switch to Asian cutoffs and the same BMI stays healthy, but the range tops out at 70.1 kg instead of 76.3 kg — the band moves, the BMI does not.
Imperial example: 5 ft 10 in at 170 lb → BMI 24.4, healthy
Enter 5 feet, 10 inches, and 170 lb: height converts to 70 × 0.0254 = 1.78 m and weight to 170 × 0.45359237 = 77.1 kg, so BMI = 77.1 ÷ (1.78 × 1.78) = 24.4, in the healthy band. The healthy range for this height is 128.9–173.5 lb, so 170 lb sits inside it, and BMI prime is 24.4 ÷ 25 = 0.98. At 180 lb the same height gives BMI 25.8 — overweight — and 6.5 lb to lose to reach 173.5 lb.
How to measure
- Measure height without shoes, standing straight against a wall, and use the morning figure if you track over time — spinal compression through the day can shave a centimetre or two off by evening, and that alone moves the BMI.
- Weigh yourself first thing in the morning, after using the bathroom and before eating, in light clothing — and use the same scale each time. A heavy meal, a full bladder, or a different scale can swing the reading by a kilogram or more.
- Enter feet and inches as two numbers, not a decimal: 5 feet 10 inches is 5 + 10, not 5.10 feet. Entering 5.10 as feet would understate your height and overstate your BMI.
- Use the Asian-cutoff toggle if it applies to you, and compare like with like over time: the same weight at the same height gives the same BMI, but the band it falls in depends on the cutoff set you chose.
- Re-measure rather than reusing an old height: adults lose height slowly with age, and an overstated height understates the BMI. If your last measurement is years old, take a fresh one before trusting the result.
Assumptions & limitations
Planning estimate
- Estimates only — not medical advice. This tool computes a screening number from height and weight; it does not diagnose, assess risk for any individual, or replace a clinician. Talk to a healthcare professional about what your result means for you.
- BMI does not measure body fat, muscle mass, bone density, or fat distribution. A muscular person can score overweight or obese without excess fat, and an older adult can score healthy while carrying excess fat with low muscle — the number needs context the tool cannot see.
- The standard bands come from WHO adult cutoffs (underweight below 18.5, healthy 18.5–24.9, overweight 25–29.9, obese 30+). The Asian cutoffs (healthy 18.5–22.9, overweight 23–27.4, obese 27.5+) follow the WHO expert consultation for Asian populations, where health risks rise at lower BMIs.
- BMI is designed for adults. It is not validated the same way for children or teenagers (who use age-and-sex percentiles), for pregnant people, or for people with conditions that change body composition — the tool does not adjust for any of these.
- The healthy range assumes your height is current and your weight is a morning, light-clothing reading. Stale heights, evening weights, or heavy clothing all shift the result, and the tool cannot detect them.
Frequently asked questions
Body mass index: weight in kilograms divided by height in metres squared. It is a screening number that puts weight in the context of height — 70 kg means something different at 1.60 m than at 1.90 m — and it sorts adults into underweight, healthy, overweight, and obese bands. It is not a body-fat measurement and not a diagnosis.
As a population screen, yes; as an individual verdict, only partly. It tracks closely with body fat across large groups, but it cannot tell muscle from fat, so athletes can score overweight without excess fat and older adults can score healthy while carrying excess fat. Treat it as a first check, not a final word — and pair it with waist circumference or a body-composition measure for the fuller picture.
On standard WHO bands, 18.5–24.9. The calculator converts that band into a weight range for your exact height: at 1.75 m it is 56.7–76.3 kg, and at 5 ft 10 in it is 128.9–173.5 lb. With Asian cutoffs the healthy ceiling drops to 22.9, so the same 1.75 m height tops out at 70.1 kg instead.
Because health risks — especially type 2 diabetes and cardiovascular disease — rise at lower BMIs in Asian populations, according to the WHO expert consultation. The healthy band ends at 22.9 instead of 24.9, overweight starts at 23, and obese at 27.5. The BMI itself is identical under either set; only the band it falls in changes.
BMI divided by 25 — the top of the standard healthy band. A prime of 0.91 (the 70 kg / 1.75 m example) sits inside the healthy band; a prime of 1.00 is exactly BMI 25; a prime of 1.20 is BMI 30, the obese threshold. It is a compact way to say how far above or below the healthy ceiling a BMI sits, without quoting the band every time.