BMI is a screening tool — consult a doctor for medical advice. Formulas follow WHO & NIH guidelines.
Body Mass Index was developed by Belgian statistician Adolphe Quetelet in the 19th century and adopted by the WHO as a population-level screening tool. For adults, BMI under 18.5 is Underweight, 18.5–24.9 is Normal weight, 25–29.9 is Overweight, and 30+ is Obese.
BMI is widely used because it requires only height and weight — but it has known limitations. It doesn't distinguish between fat and muscle mass, so muscular athletes often show as 'overweight'. It's also less accurate for elderly populations (who lose muscle mass) and doesn't account for fat distribution (central/abdominal fat carries more health risk than hip/thigh fat). Use BMI as one data point among several, not as a standalone health diagnosis.
Common real-world scenarios where this tool saves time.
Track BMI changes over time to understand broad trends in your weight relative to height.
Use BMI as one of several metrics when setting weight goals alongside body fat percentage and waist circumference.
Healthcare professionals use BMI to screen for weight categories that may correlate with health risks.
Some health insurance applications ask for BMI — calculate it here before filling out forms.
If assessing someone under 18, use CDC or WHO BMI-for-age percentile charts — adult cutoffs on this page do not apply.
Input
Height: 175 cm · Weight: 70 kgOutput
BMI: 22.9 — Normal weight (18.5–24.9)BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.86. Healthy range for 175 cm: approximately 57–76 kg. This person is in the middle of the normal range.
Input
Height: 180 cm · Weight: 95 kg (rugby player, ~12% body fat)Output
BMI: 29.3 — classified as OverweightA rugby player with 95 kg and 12% body fat is healthier than the BMI suggests. BMI can't distinguish between muscle and fat — 95 kg of mostly muscle looks the same as 95 kg of mostly fat. Use body fat % for more meaningful assessment in athletic individuals.
Input
Height: 5 ft 10 in (70 in) · Weight: 180 lbsOutput
BMI: 25.8 — Overweight (25.0–29.9)Imperial formula: BMI = 703 × 180 ÷ 70² = 126,540 ÷ 4,900 = 25.82. Healthy weight range at 5 ft 10 in is roughly 129–173 lbs (BMI 18.5–24.9). This result sits just above the normal ceiling — waist circumference and body composition add important context.
Input
Height: 170 cm · Weight: 72 kg · Age 68Output
BMI: 24.9 — upper Normal weight rangeBMI = 72 ÷ (1.70)² = 24.91, at the top of the WHO normal band. For adults over 65, clinicians sometimes interpret BMI 22–27 as reasonable because age-related muscle loss can make a 'normal' BMI mask higher body fat. Pair with waist measurement and a healthcare review rather than relying on the number alone.
Standard BMI ranges for adults. Some guidelines use different thresholds for specific populations (e.g., lower cutoffs in some Asian clinical guidelines).
| BMI Range | Category | Health Risk (general) |
|---|---|---|
| Below 18.5 | Underweight | Increased risk (nutrient deficiency, bone loss) |
| 18.5 – 24.9 | Normal weight | Lowest risk range |
| 25.0 – 29.9 | Overweight | Moderate risk (elevated blood pressure, cholesterol) |
| 30.0 – 34.9 | Obese Class I | High risk |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40 and above | Obese Class III (morbid obesity) | Extremely high risk |
BMI is a screening tool, not a diagnostic measure. Interpret alongside waist circumference, body fat %, blood pressure, and clinician guidance.
BMI is one of several indicators used to assess weight-related health risk. Each has trade-offs.
| Metric | What it measures | Advantage over BMI | Key limitation |
|---|---|---|---|
| BMI | Weight relative to height squared | Simple; requires no equipment; widely used in clinical literature | Cannot distinguish muscle from fat |
| Waist circumference | Abdominal fat (visceral fat) | Directly measures dangerous central fat deposit | Does not account for height |
| Waist-to-height ratio | Waist size relative to height | Strong predictor of metabolic and cardiovascular risk | Less established in clinical guidelines |
| Body fat % | Proportion of total mass that is fat | Accurately distinguishes muscle from fat | Requires calipers or DEXA scan for accuracy |
| Waist-to-hip ratio | Fat distribution pattern (apple vs pear) | Assesses cardiovascular risk from fat distribution shape | Less predictive than waist circumference alone |
WHO recommends using BMI alongside waist circumference for a more complete cardiovascular risk assessment in clinical settings.
How EverydayTools compares to common free BMI calculators for privacy, units, and result depth.
| Tool | Privacy | Metric + imperial | Healthy range | Visual scale | Copy / share | Signup required |
|---|---|---|---|---|---|---|
| EverydayTools | Browser-only ✓ | ✓ | ✓ | ✓ | ✓ | No |
| CDC Adult BMI Calculator | Browser (cdc.gov) | ✓ | Limited | No | No | No |
| NHS healthy weight checker | Browser (nhs.uk) | ✓ | ✓ | No | No | No |
| Calculator.net BMI | May use server analytics | ✓ | ✓ | Chart on some pages | Copy text | Optional account |
| Healthline BMI calculator | Editorial site + ads | ✓ | ✓ | Category chart | Social share | No |
Feature availability changes over time — verify on each site before relying on it for clinical decisions.
BMI is not one-size-fits-all. Use the right screening method for each population.
| Population | Recommended approach | Threshold notes | This calculator |
|---|---|---|---|
| Adults 18+ | Standard WHO BMI categories | <18.5 / 18.5–24.9 / 25–29.9 / ≥30 | ✓ Designed for this group |
| Asian-Pacific adults | BMI + clinician context | Overweight often screened at ≥23; high risk ≥27.5 | Shows WHO standard; see FAQ for Asia-Pacific guidance |
| Children & teens (under 18) | CDC/WHO BMI-for-age percentile charts | Percentiles, not fixed adult cutoffs | ✗ Use paediatric charts, not this tool |
| Athletes / high muscle mass | Body fat % or waist circumference | BMI often overestimates fat risk | Use Body Fat Calculator for follow-up |
| Adults 65+ | BMI + waist + clinical review | Optimal range often cited as BMI 22–27 | ✓ Screening start; interpret with provider |
This page screens adults with standard WHO formulas. It does not replace population-specific clinical protocols.
BMI is computed from height and weight using the Quetelet index formula developed in the 1830s and adopted by the WHO as a population-level screening tool. The calculator maps the result to standard adult categories and derives the healthy weight range by back-calculating the 18.5–24.9 BMI range at the entered height.
Formula
Metric: BMI = weight(kg) ÷ height(m)²
Imperial: BMI = 703 × weight(lb) ÷ height(in)²
Healthy weight range: lower = 18.5 × height(m)²; upper = 24.9 × height(m)²BMI identifies statistical risk at a population level — a BMI of 27 does not mean you have or will develop any condition. Interpret it alongside waist circumference, blood pressure, cholesterol, and a clinician's assessment before drawing conclusions.
For people under 20, standard WHO BMI cutoffs do not apply. Children use BMI-for-age percentile charts from the CDC or WHO. A BMI that is 'normal' for an adult may be in the overweight percentile for a 10-year-old, and vice versa.
BMI divides weight by height² and cannot distinguish muscle from fat. Professional athletes, bodybuilders, and people with high muscle mass regularly show as 'overweight' or 'obese' while having low body fat. Use the body fat calculator for a composition-aware assessment.
Imperial BMI requires the 703 multiplier: BMI = 703 × weight(lbs) ÷ height(in)². Without it, the result is roughly 6× smaller than the actual BMI. Always verify your calculator uses the correct formula for the selected unit system.
Asian and Asian-Pacific populations show increased cardiometabolic risk at lower BMI values. WHO Asia-Pacific guidelines suggest screening at BMI ≥23 (overweight) and ≥27.5 (obese equivalent) rather than 25 and 30. Discuss with your healthcare provider if these thresholds are relevant to you.
BMI cannot distinguish muscle from fat. A 90 kg athlete with 10% body fat will score as 'overweight' using BMI. Use the Body Fat Calculator (which applies the US Navy measurement method) or DEXA scan for composition-aware assessment.
Adult BMI categories (18.5–24.9 normal) do not apply to children or teenagers. Paediatric weight assessment uses BMI-for-age percentile charts from the CDC or WHO, which compare to a reference population of the same age and sex.
BMI is a screening tool that flags population-level statistical risk, not an individual diagnosis. A single BMI number cannot diagnose obesity, metabolic syndrome, or any specific condition. Clinical assessment requires waist circumference, lab results, blood pressure, and a clinician's evaluation.
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For adults, the WHO classifies BMI as: Under 18.5 = Underweight, 18.5–24.9 = Normal weight, 25–29.9 = Overweight, 30+ = Obese. These thresholds are for adults only — children use age- and sex-specific percentile charts from the CDC or WHO.
BMI is a population screening tool, not a diagnostic measure. It correlates with body fat at a population level but cannot distinguish muscle from fat for individuals. Athletes often show as overweight or obese on BMI despite low body fat. Always interpret BMI alongside waist circumference, body fat percentage, blood pressure, and a clinician's assessment.
A BMI of 30 or higher is classified as obese. The WHO further divides obesity into Class I (30–34.9), Class II (35–39.9), and Class III / morbid obesity (40 and above). Each class carries progressively higher cardiovascular, metabolic, and surgical risk.
Yes. BMI cannot distinguish between muscle and fat — both add weight. A professional rugby player at 180 cm and 100 kg has a BMI of 30.9 (obese range) but may have 12% body fat and excellent cardiovascular health. For muscular individuals, the body fat percentage calculator is more informative than BMI.
The BMI formula itself doesn't change with age, but its accuracy as a health indicator does. Older adults (65+) often lose muscle mass while gaining fat, so a 'normal' BMI can mask unhealthy body composition. Some clinical guidelines recommend a slightly higher BMI target for adults over 65 to account for this.
Morbid obesity, also called Class III obesity or severe obesity, refers to a BMI of 40 or higher. At this level, the risk of obesity-related conditions — including type 2 diabetes, heart disease, sleep apnea, and certain cancers — is significantly elevated. Weight-loss surgery (bariatric surgery) is often considered at BMI ≥40 or ≥35 with serious comorbidities.
No — the standard BMI formula (weight/height²) is the same for both. However, men and women naturally have different body fat distributions at the same BMI. Women typically have higher body fat than men at the same BMI due to physiological differences. Some research suggests sex-specific BMI thresholds may be more meaningful, but the WHO and CDC still use the same universal categories.
Standard WHO BMI categories were validated primarily on middle-aged adults. For adults over 65, a BMI in the 22–27 range is often considered optimal — the slight upward adjustment accounts for age-related muscle loss and the protective effect of modest weight reserves during illness. Discuss interpretation with your healthcare provider.
For Asian and Asian-Pacific populations, WHO expert consultation suggests increased cardiometabolic risk at lower BMI values: overweight from BMI ≥23 and high-risk ranges from BMI ≥27.5. Select Asia-Pacific mode in the calculator to apply these category cutoffs and healthy-weight band (18.5–22.9). Discuss population-specific interpretation with your healthcare provider.
Children and teens are still growing, so a single BMI number cannot be compared to fixed adult cutoffs. Paediatric assessment uses BMI-for-age and sex percentile charts from the CDC or WHO — for example, the 85th percentile may indicate overweight and the 95th obesity for a given age. This calculator is for adults 18+ only; use official paediatric charts for anyone under 18.
Stand barefoot on a flat surface with heels together, back straight, and head level. Measure at the end of a normal exhale without shoes. Use a wall-mounted stadiometer or a flat tape measure from floor to the top of the head. For imperial entry, convert to feet and inches (not meters in a centimetre field). Small height errors disproportionately affect BMI because height is squared in the formula.
Core BMI calculations run entirely in your browser using JavaScript — height and weight are not sent to EverydayTools servers. If you enable 'Save my inputs locally', values are stored only in your device's browser storage (localStorage) and can be cleared by resetting the tool or clearing site data. Open your browser Network tab while calculating to confirm no upload requests carry your inputs.
WHO guidance recommends pairing BMI with waist circumference for a fuller cardiovascular risk picture. Elevated waist circumference — generally above 94 cm (37 in) for men and 80 cm (31.5 in) for women — can signal excess abdominal fat even when BMI is in the normal range. BMI alone cannot detect central obesity; waist measurement adds distribution context BMI misses.
After entering valid height and weight, click Copy result for a text summary, or Share to copy a link that restores your inputs (including optional waist and unit/standard settings). On mobile, Share opens the native share sheet when supported. Nothing is uploaded — sharing only packages data you choose to send.
BMI stands for Body Mass Index — a ratio of body weight to height squared (kg/m²) used as a population-level screening tool for weight categories. It was developed from the Quetelet index and adopted by the WHO for adult epidemiological and clinical screening.
Convert height to metres. Square that value. Divide weight in kilograms by height². Example: 70 kg and 1.75 m → 1.75² = 3.0625 → 70 ÷ 3.0625 = 22.9. In imperial units use BMI = 703 × weight(lbs) ÷ height(inches)².
BMI = 703 × weight in pounds ÷ (height in inches)². The factor 703 converts imperial units to the same kg/m² scale as the metric formula. Enter feet and inches separately in this calculator — do not enter total inches in the feet field.
WHO subdivides obesity: Class I is BMI 30–34.9, Class II is 35–39.9, and Class III (severe/morbid obesity) is BMI ≥40. Higher classes correlate with greater cardiometabolic and surgical risk. This calculator displays all three classes separately.
Standard adult BMI categories are not designed for pregnancy. Weight gain targets depend on pre-pregnancy BMI and gestational week — use prenatal care guidance from your midwife or obstetrician rather than adult screening cutoffs alone.
Yes. Muscle weighs more than fat per volume, so muscular people often score as overweight or obese despite low body fat. That is why athletes should pair BMI with body fat percentage, waist circumference, or clinical assessment.
The same WHO formula applies to women and men. For standard international cutoffs, a BMI of 18.5–24.9 is classified as normal weight. Women typically carry more body fat than men at the same BMI, so waist measurement adds useful context.
Men use the identical BMI formula and standard adult categories. Normal weight is generally 18.5–24.9 on WHO international cutoffs. Central fat (waist) is a strong risk marker for men — thresholds often cite ≥94 cm (37 in) or ≥90 cm (35 in) in Asia-Pacific guidance.
Multiply your height in metres squared by 18.5 and 24.9 (or 18.5–22.9 in Asia-Pacific mode) to get a healthy weight band. This calculator shows that range automatically after you enter height and weight.
Sustainable change usually combines modest calorie adjustment, increased activity, adequate protein, sleep, and professional support when BMI is in overweight or obese classes. Avoid crash diets. Use our calorie calculator for maintenance targets after screening with BMI.
Focus on nutrient-dense meals, adequate protein, strength training to build lean mass, and medical evaluation if unintended weight loss occurred. A dietitian can personalize calorie and micronutrient targets beyond what BMI alone suggests.
WHtR divides waist circumference by height. Values ≥0.5 are used in some guidelines (including NICE) to flag increased central adiposity, even when BMI is normal. This calculator shows WHtR when you enter an optional waist measurement.
Yes. The calculator is free, requires no account, and runs entirely in your browser. Optional local save stores inputs only on your device.
They answer different questions. BMI is a quick weight-for-height screen; body fat percentage estimates fat mass directly. For athletes or older adults, body fat or waist often adds more individual insight than BMI alone.
Monthly or quarterly checks are enough for most people tracking general trends. Daily fluctuations reflect water and food weight, not meaningful fat change. Log occasionally with the optional on-device history feature if you want a simple trend view.
No. BMI is one screening input. Cardiovascular risk also depends on blood pressure, lipids, smoking, diabetes, family history, and waist fat. Elevated BMI raises population-level statistical risk but cannot diagnose any condition for an individual.
A BMI below 18.5 is classified as underweight for adults on WHO international cutoffs. Very low BMI may reflect malnutrition or underlying illness — seek medical advice if unintentional weight loss or deficiency symptoms are present.
BMI calculations run entirely in your browser using JavaScript. Height and weight are not uploaded to EverydayTools servers. Optional local save uses browser localStorage on your device only — disable it or click Reset to clear stored inputs.
BMI results match WHO and CDC adult formulas for equivalent metric inputs. Imperial results may differ by ±0.1–0.2 from metric due to the 703 approximation and rounding during unit conversion — use metric for the most consistent result.
Every BMI calculation runs in client-side JavaScript. Open your browser Network tab while entering height and weight — no requests should carry your body measurements to external servers.
Cross-check by calculating manually: metric BMI = kg ÷ (height in metres)²; imperial BMI = 703 × lbs ÷ (total inches)². Compare your result to the CDC adult BMI calculator or NHS healthy weight checker using the same height and weight.
Limitations: Adult WHO categories only (18+). Does not replace waist circumference, body fat measurement, lab tests, or clinical diagnosis. Asian-Pacific population thresholds (23 / 27.5) are documented in FAQs but this tool displays standard WHO adult cutoffs.
General BMI screening estimate only—not medical advice. Consult a healthcare provider for diagnosis, treatment, or weight-management decisions.
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Reviewed by EverydayTools Editorial Team on 2026-06-07.
BMI calculator
Instant BMI with six adult categories, healthy weight range, and visual scale — 100% in your browser.
BMI is a screening tool — consult a doctor for medical advice. Formulas follow WHO & NIH guidelines.
Measure around your bare abdomen at navel level after a normal exhale. Pairing waist with BMI improves screening for central obesity.
Under 18 triggers pediatric guidance.
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Calculations run in your browser — height and weight are never uploaded.