Free bmi calculator
Find your body mass index in two seconds. Enter your height and weight in metric or imperial. The calculator returns your BMI, the World Health Organization weight category it falls in, and a plain-language read on what the number means — updated live, as you type.
On this page18 sections
BMI is a screening tool, not a diagnosis. How accurate is this?
Results are estimates. Consult a professional.
How the BMI calculator works
Body mass index puts your weight and height on a single scale so the same number means the same thing for a tall person and a short one. You type your height and weight; the calculator divides one by the other and matches the result to the World Health Organization category bands.
- weight in kilograms (or pounds, with the 703 factor)
- height in metres (or inches), squared
- 703 converts the imperial result to the same scale as metric
What your BMI means
BMI sorts adults into four bands. The number itself is less important than which band it lands in, and even then the band is a starting point for a conversation, not a verdict.
| Category | BMI range |
|---|---|
| Underweight | below 18.5 |
| Normal (healthy) weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese | 30.0 and above |
Source: World Health Organization adult BMI classification. Applies to adults aged 20 and over; the same cut-offs apply to men and women.
These cut-offs come directly from the WHO. The CDC publishes the same adult bands and recommends BMI as a population-level screening measure, not a diagnostic test.Healthy weight range for your height
BMI works in reverse, too. Instead of asking what your number is, you can ask what weight would put you in the healthy band at your height. A BMI between 18.5 and 24.9 is the WHO healthy range, so every height has a weight span that lands inside it. The table below shows that span for common heights, in both kilograms and pounds — find your height and read across.
| Height | Healthy weight (kg) | Healthy weight (lb) |
|---|---|---|
| 4'10" (147 cm) | 40 – 54 kg | 88 – 119 lb |
| 5'0" (152 cm) | 43 – 58 kg | 94 – 127 lb |
| 5'2" (157 cm) | 46 – 61 kg | 101 – 135 lb |
| 5'4" (163 cm) | 49 – 66 kg | 108 – 146 lb |
| 5'6" (168 cm) | 52 – 70 kg | 115 – 155 lb |
| 5'8" (173 cm) | 55 – 75 kg | 122 – 164 lb |
| 5'10" (178 cm) | 59 – 79 kg | 129 – 174 lb |
| 6'0" (183 cm) | 62 – 83 kg | 137 – 184 lb |
| 6'2" (188 cm) | 65 – 88 kg | 144 – 194 lb |
| 6'4" (193 cm) | 69 – 93 kg | 152 – 204 lb |
Ranges are the weights that keep BMI between 18.5 and 24.9 at each height, rounded to the nearest unit. They are the same for men and women, and apply to adults aged 20 and over.
The 18.5–24.9 healthy band is the World Health Organization's adult classification, also published by the US National Institutes of Health (NIH) and the CDC. Enter your exact height above and the calculator shows your personal healthy-weight range.A worked example using the BMI calculator
Maya is 1.70 m tall and weighs 70 kg. She wants to know which BMI band she falls in. Here is the arithmetic the calculator runs.
Step 1 — Square the height
Height in metres, squared: 1.70 × 1.70 = 2.89.
Step 2 — Divide weight by that figure
70 ÷ 2.89 = 24.2. The imperial cross-check (154 lb, 66.9 in) gives 703 × 154 ÷ 66.9² ≈ 24.2 — the same answer.
Step 3 — Match it to a category
24.2 sits inside the 18.5–24.9 band, so Maya's BMI is in the normal, healthy range.
When to use this BMI calculator
BMI is a quick screening number. Reach for it when you want a fast, standardised read, and pair it with other measures when the stakes are higher.
- For a quick self-check — to see roughly where your weight sits relative to your height.
- Before a doctor's visit — to walk in with a number your clinician will recognise and can build on.
- To track a trend — to watch the figure move over weeks or months as your weight changes.
- For population comparisons — BMI is what public-health bodies use to compare groups, so it is the common currency.
Is BMI different for men and women?
No. BMI uses one formula and one set of category cut-offs for everyone — weight in kilograms divided by height in metres squared, with the same 18.5, 25, and 30 boundaries for men and women alike. The calculation does not ask your sex, and it does not adjust for it.
What differs is what the same number is made of. At an identical BMI, men typically carry more muscle and women more essential fat — body fat that is necessary for hormonal and reproductive health. A healthy adult woman might sit around 21–33% body fat where a man at the same BMI sits nearer 8–20%. That means BMI can read the same for two people whose body composition is quite different, and it can read "normal" for a woman whose body fat is higher than her BMI suggests, or "overweight" for a muscular man whose fat is low.
BMI for children and teens
For anyone aged 2 to 19, the adult cut-offs above do not apply. Children's bodies change shape constantly as they grow, and a BMI that is perfectly healthy at age 6 would mean something different at age 16. So BMI for young people is read not against fixed numbers but against percentiles — how a child compares with thousands of others of the same age and sex on the CDC growth charts.
| Category (ages 2–19) | BMI-for-age percentile |
|---|---|
| Underweight | below 5th |
| Healthy weight | 5th – 84th |
| Overweight | 85th – 94th |
| Obese | 95th and above |
A child at the 60th percentile, for example, has a higher BMI than 60% of children their age and sex — squarely in the healthy band. The raw BMI number is still calculated the same way; it is the interpretation that changes.
The percentile categories come from the CDC's BMI-for-age growth charts for ages 2–19. This calculator uses the adult WHO bands and is intended for ages 20 and over; for a younger person, use a dedicated child-and-teen BMI tool that plots BMI-for-age.BMI and your health risks
The reason BMI bands exist at all is that, across large populations, where you sit on the scale tracks with your statistical risk of certain conditions. A higher BMI is associated with a greater likelihood of type 2 diabetes, high blood pressure, cardiovascular disease, stroke, and several cancers, because excess body fat — particularly around the organs — changes how the body handles blood sugar, fats, and inflammation. At the other end, a very low BMI is associated with nutritional deficiency, a weakened immune response, loss of bone density, and, in some cases, reduced fertility.
The key word is associated. These are population-level patterns, not a prediction about any one person. A high BMI does not guarantee disease, and a healthy BMI does not guarantee its absence — fitness, diet quality, blood pressure, blood sugar, family history, and where fat is carried all weigh in. BMI flags a question worth asking; it does not answer it.
BMI vs. body fat percentage
BMI and body fat percentage answer different questions. BMI asks how heavy you are for your height; body fat percentage asks how much of that weight is actually fat. BMI is free and takes one division. Body fat percentage needs callipers, a smart scale, or a DEXA scan — more accurate, more effort.
The gap matters most at the edges. A muscular person can show a high BMI with low body fat, while someone with little muscle can sit in a normal BMI band yet carry a high fat percentage ("normal-weight obesity"). For day-to-day screening BMI is enough; when body composition is the real question, body fat percentage is the better tool.
| Measure | Tells you | Effort |
|---|---|---|
| BMI | Weight relative to height | Instant, free |
| Body fat % | Share of weight that is fat | Callipers / scan |
The Free body fat calculator estimates the second number when BMI alone is not enough.
BMI vs. waist-to-height ratio
BMI's biggest blind spot is where fat sits. Two people with the same BMI can carry their weight very differently, and fat stored around the abdomen — visceral fat, packed around the organs — is the kind most strongly linked to metabolic and heart risk. BMI cannot see it. Waist-to-height ratio can.
The measure is as simple as BMI: divide your waist circumference by your height, in the same units. A widely used rule of thumb is to keep your waist to less than half your height — a ratio under 0.5. So someone 170 cm tall is aiming for a waist under 85 cm; someone 5'10" (70 in) for a waist under 35 in. Because it captures central fat directly, waist-to-height ratio often catches risk that BMI misses, including in people whose BMI sits in the normal band.
| Waist ÷ height | What it suggests |
|---|---|
| Below 0.5 | Lower central-fat risk |
| 0.5 – 0.6 | Raised risk — worth a closer look |
| 0.6 and above | Higher central-fat risk |
How to reach a healthy BMI
If your BMI sits outside the healthy band, the goal is rarely the number itself — it is the health that moves with it. The encouraging part: you do not have to reach a "perfect" BMI to benefit. Research consistently shows that a 5–10% change in body weight brings meaningful improvements in blood pressure, blood sugar, and cholesterol, long before someone reaches a textbook BMI.
Weight changes through energy balance. To lose weight you need a modest, sustainable calorie deficit; to gain, a modest surplus. A safe, evidence-based pace is about 0.5–1 kg (1–2 lb) per week — faster than that tends to cost muscle and rebound. But the number on the scale is only part of it. Diet quality matters as much as quantity: more whole foods, fibre, and protein, less ultra-processed food. Regular activity protects muscle and improves the metabolic markers BMI never sees, and adequate sleep supports the appetite hormones that make any plan workable.
Limitations of BMI
BMI works because it is simple, and it misleads for the same reason. It uses only height and weight, so it cannot see what the weight is made of or how it is distributed.
Muscle reads as excess weight
Muscle is denser than fat. Athletes and heavy lifters often score overweight or obese on BMI while carrying very low body fat. The number is high; the health risk it implies is not there.
Age and ethnicity shift the meaning
Older adults lose muscle and may carry more fat at the same BMI. The risk thresholds also differ by ancestry: many health bodies apply a lower overweight cut-off (around 23) for people of South and East Asian descent, who face metabolic risk at lower BMIs.
BMI definitions
How accurate is this BMI calculator?
The arithmetic is exact. BMI is computed with the standard formula published by the World Health Organization and the CDC — weight in kilograms divided by height in metres squared, with the 703 factor applied for imperial inputs — and the result is matched to the WHO adult category bands. The healthy-weight range shown is the weight span that keeps your BMI between 18.5 and 24.9 at your height.
What the calculator cannot do is judge your body composition. BMI does not separate muscle from fat, does not account for where fat sits, and uses adult cut-offs that do not apply to children, who are assessed on CDC age- and sex-specific percentile charts. Use this number as a screen, then confirm with a healthcare professional who can weigh it against your waist measurement, body fat, age, and history.
Frequently asked questions about the free bmi calculator
About this BMI calculator
This BMI calculator runs entirely in your browser. Your height and weight never leave your device — nothing is sent to a server, logged, or shared. BMI is computed with the standard WHO formula (weight in kilograms ÷ height in metres squared), and the result is matched against the WHO adult category bands, updating instantly on every change.
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