To calculate your BMI, divide your weight in kilograms by your height in metres squared — BMI = kg ÷ m² — or enter metric (cm/kg) or imperial (ft/in/lb) measurements into the BMI Calculator, which also shows your category, the healthy weight range for your height, your BMR and a daily-calorie (TDEE) table by activity level. A person who is 175 cm tall and weighs 70 kg has a BMI of 22.9, inside the healthy band of 18.5–24.9. One warning belongs at the top: BMI is a screening number, not a diagnosis — this guide explains both the maths and its real limits. General information only, not medical advice.
Please read this first: BMI does not measure body fat and does not diagnose anything. It misleads for athletes and very muscular people, children, pregnant women and many older adults. If a result worries you, talk to a doctor or dietitian rather than acting on a calculator — including this one.
The Formula and the Categories
BMI = weight (kg) ÷ height (m)². The squaring is the part people drop: divide by your height twice, not once. For imperial measurements the calculator converts first (pounds to kilograms, feet and inches to metres) and then applies the same formula, so both systems land on the same scale:
| BMI | Category | What it means, honestly |
|---|---|---|
| Under 18.5 | Underweight | Below the healthy band for most adults; worth a conversation with a clinician, especially if unintentional |
| 18.5–24.9 | Healthy | The reference band for the general adult population |
| 25–29.9 | Overweight | Above the band; a prompt to look at the whole health picture, not a verdict on its own |
| 30 and above | Obese | Well above the band; clinicians use it as one screening input among several |
BMI category thresholds and the worked example (175 cm, 70 kg → BMI 22.9) — hover or tap each bar for details.
How to Use the BMI Calculator, Step by Step
- Choose your units. Metric (centimetres and kilograms) or imperial (feet, inches and pounds) — the BMI Calculator converts imperial entries before calculating.
- Enter height and weight as they are. Measured, current figures — shoes off, honest weight. The formula can only describe the numbers it is given.
- Add sex and age. These do not change BMI itself; they power the BMR estimate below it, which does depend on them.
- Read all the outputs as a set. Your BMI and category, the healthy weight range for your height (far more actionable than the single number), your BMR, and the TDEE table showing estimated daily calories at each activity level.
- Hold the result at arm's length. Note it, consider the limits section below, and treat any concern as a reason to talk to a professional — not as a self-diagnosis.
Worked Example: 175 cm and 70 kg
Height 175 cm is 1.75 m. Square it: 1.75 × 1.75 = 3.0625. Divide the weight: 70 ÷ 3.0625 = 22.857…, which rounds to a BMI of 22.9 — comfortably inside the healthy band. The healthy weight range for this height comes from running the band edges backwards: 18.5 × 3.0625 ≈ 56.7 kg at the bottom and 24.9 × 3.0625 ≈ 76.3 kg at the top, so the healthy range is roughly 56.7–76.3 kg. That range is the genuinely useful output: it tells a 70 kg person they sit mid-band, and it tells an 80 kg person at the same height exactly how far above the band's top they are (80 ÷ 3.0625 ≈ 26.1, in the overweight band) without any drama.
BMR and TDEE: The Calorie Side of the Same Page
The tool also estimates basal metabolic rate with the Mifflin–St Jeor equation: for men, BMR = 10 × kg + 6.25 × cm − 5 × age + 5; for women, the same formula ending in − 161 instead of + 5. For a 30-year-old man at our example's 70 kg and 175 cm: 700 + 1,093.75 − 150 + 5 = 1,648.75, about 1,649 kcal a day — the energy the body uses at complete rest. Total daily energy expenditure then scales BMR by activity: TDEE = BMR × a factor from 1.2 (sedentary) up to 1.9 (very active). Our example at sedentary gives 1,649 × 1.2 ≈ 1,979 kcal a day; at the very active end, 1,649 × 1.9 ≈ 3,133 kcal. The spread between those two numbers — over 1,100 kcal — is why activity honesty matters more than formula precision. Our companion guide, how to calculate your daily calories, works BMR and TDEE in full, including how to test an estimate against real weeks of eating and weighing.
| Activity level | Factor | Example TDEE (BMR 1,649) |
|---|---|---|
| Sedentary | × 1.2 | ≈1,979 kcal/day |
| Very active | × 1.9 | ≈3,133 kcal/day |
Only the endpoints are shown here because they are the figures stated for the tool; the calculator's own table fills in the levels between them. Even the endpoints are population estimates — two people with identical height, weight, age and sex can differ meaningfully, which is why the calorie guide's trend-testing method exists.
The Limits of BMI, Stated Prominently
BMI survives in medicine because it is cheap, standardised and useful across populations — not because it describes any individual body well. It does not measure body fat, fat distribution, muscle, bone density or fitness. A rugby player and a sedentary person can share a BMI of 28 with entirely different health profiles, because muscle is denser than fat and the formula cannot tell them apart. It was designed for adults, so it misleads for children and teenagers, whose healthy ranges shift with age and development; it does not apply during pregnancy; and it can flatter older adults who have lost muscle while keeping weight. Use it the way screening tools are meant to be used: as a first signal that sorts out who should look closer, with a professional doing the closer looking.
Five Mistakes People Make With BMI
- Forgetting to square the height. Weight ÷ height is not BMI. At 70 kg and 1.75 m, the wrong maths gives 40 — a frightening number produced by a missing step, not by a body.
- Mixing units mid-formula. Pounds into the kilogram formula, or centimetres where metres belong, produces nonsense that still looks like a number. Use the calculator's unit switcher, or convert everything first.
- Treating the category as a diagnosis. A BMI of 30 is a screening flag, not a finding of illness; a BMI of 22 is not a certificate of health. Blood pressure, blood work, fitness and history all sit outside this one ratio.
- Applying adult bands to children or pregnancy. The 18.5–24.9 band is an adult reference. Children need age- and sex-specific percentiles, and pregnancy needs its own clinical guidance.
- Chasing the number instead of the range. The healthy weight range for your height (56.7–76.3 kg in the example) is a target you can actually use. A single BMI point, re-measured daily, mostly measures water and worry.
Related Tools and Guides
- BMI Calculator — the tool used in this guide: BMI, category, healthy weight range, BMR and a TDEE table by activity level.
- Calorie Calculator — go deeper on BMR and TDEE once you know your BMI.
- Percentage Calculator — handy for the percentage changes behind weight trends.
- How to calculate your daily calories — BMR, TDEE and honest goal ranges, worked in full.
Run a clinic, gym or wellness business and want honest health calculators like this one on your own website? Book a free consultation with Asad Webs
Frequently Asked Questions
How do I calculate my BMI?
Divide your weight in kilograms by your height in metres squared: BMI = kg ÷ m². For 70 kg at 1.75 m: 70 ÷ 3.0625 = 22.9. The BMI Calculator does it from metric or imperial entries and shows your category and healthy weight range.
What is a healthy BMI?
For most adults, 18.5 to 24.9 is the healthy reference band; under 18.5 is classed underweight, 25 to 29.9 overweight, and 30 or above obese. It is a screening band for populations, not a personal diagnosis.
What is the healthy weight range for my height?
Multiply the band edges by your height in metres squared. At 175 cm (height squared = 3.0625): 18.5 × 3.0625 ≈ 56.7 kg to 24.9 × 3.0625 ≈ 76.3 kg. The calculator shows this range for any height.
How is BMR calculated?
With the Mifflin–St Jeor equation: men, 10 × kg + 6.25 × cm − 5 × age + 5; women, the same but − 161 at the end. A 30-year-old man of 70 kg and 175 cm gets about 1,649 kcal a day.
What is TDEE and how does it relate to BMI?
TDEE is your estimated total daily energy expenditure: BMR multiplied by an activity factor from 1.2 (sedentary) to 1.9 (very active). BMI itself has no activity component; the calculator simply presents both on one page.
Why is my BMI high when I am muscular?
Because BMI cannot distinguish muscle from fat — it only knows total weight and height. Athletes and very muscular people are the classic case where BMI misleads, which is why it is a screening number rather than a diagnosis.
Can children use the adult BMI categories?
No. The 18.5–24.9 band is an adult reference; children and teenagers need age- and sex-specific percentile charts, and pregnancy is assessed differently again. A clinician can interpret a child's growth properly.
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