# BMI Calculator with Body Fat Estimate (kg and lbs) > Calculate your BMI from height and weight in seconds. See your category, the formula in kg and lbs, and what the number actually says about body composition. - Canonical page: https://www.recompai.com/tools/bmi - Language: en - Other languages: [es](https://www.recompai.com/es/tools/bmi), [pt](https://www.recompai.com/pt/tools/bmi), [de](https://www.recompai.com/de/tools/bmi), [it](https://www.recompai.com/it/tools/bmi), [fr](https://www.recompai.com/fr/tools/bmi) Enter height and weight to get your BMI, WHO category, and the body-composition blind spot to check next. ## What is BMI? BMI is your weight in kilograms divided by your height in meters squared. The result places you in one of four WHO bands: underweight, healthy, overweight, or obese. The formula was built in the 1830s by Adolphe Quetelet to model population distributions, not to screen individuals. That is why it stays useful as a fast orientation and falls short as a body composition measurement. ## BMI categories WHO classifies BMI into four screening bands. Underweight < 18.5 Below the WHO healthy range Healthy 18.5–24.9 WHO healthy range Overweight 25–29.9 Above the standard BMI range. BMI alone cannot show body composition. Obesity ≥ 30 BMI 30–39.9. Metabolic risk rises with BMI here. Classified as severe at ≥ 40. ## The BMI formula in kg and lbs Two unit systems, one number. Use whichever you measure in. Metric kg / m² 80 kg / (1.80 m)² = 24.7 Imperial 703 × lbs / in² 703 × 176 lbs / (71 in)² = 24.5 Both formulas return the same number once units are converted. The 703 multiplier in the imperial version is the conversion constant baked in. ## BMI reference by age The WHO bands apply to all adults. Some studies find a slightly higher healthy range correlates with better outcomes after 50. Age Healthy band What it means 19–24 19.0–24.0 19.0–24.0Lean tissue is at peak. Healthy band sits low. 25–34 20.0–25.0 20.0–25.0Metabolism shifts. The healthy band shifts with it. 35–44 21.0–26.0 21.0–26.0Muscle loss begins without resistance training. 45–54 22.0–27.0 22.0–27.0Bone density and lean mass both trend down. 55–64 23.0–28.0 23.0–28.0A slightly higher BMI tracks with longevity outcomes. 65+ 24.0–29.0 24.0–29.0Underweight carries more risk than mild overweight. BMI is a population screening tool, not a diagnosis. The bands above are research-informed orientation, not clinical advice. ## BMI cannot separate fat from muscle BMI cannot tell fat from muscle. Two people with identical BMI can have body-fat percentages 10 points apart. The formula is weight divided by height squared. It was built in the 1830s by Adolphe Quetelet to model population distributions, not to screen individuals. Every kilogram counts the same regardless of whether it is fat or lean tissue. BMI tracks weight relative to height, not fat and muscle separately. During recomposition, BMI may fall, stay similar or rise. Even when it changes, it cannot tell you which tissue changed. Compare it with body measurements and training progress. Body-fat estimates add information that BMI cannot provide, but neither proves recomposition. Review body-fat estimates alongside weight, waist and training progress, using consistent measurement methods. ## BMI and body recomposition, explained Questions people search when BMI says one thing and the mirror says another. ### Does BMI change during body recomposition? BMI tracks weight relative to height, not fat and muscle separately. During recomposition, BMI may fall, stay similar or rise. Even when it changes, it cannot tell you which tissue changed. Compare it with body measurements and training progress. ### What BMI is best for starting body recomposition? When fat loss is the priority and body fat is higher, a modest deficit may be a useful starting point. Leaner people or those prioritizing training and muscle gain may start closer to maintenance. Adjust from your observed progress, not a fixed rule for every body. ### Is BMI accurate for muscular people? No. BMI treats every kilogram identically regardless of whether it is fat or muscle. A competitive athlete at 12% body fat can have a BMI in the overweight range. For anyone who lifts consistently, body fat % is a far more accurate health indicator than BMI. ### Why does my BMI stay the same even though I am losing fat? BMI tracks weight relative to height, not fat and muscle separately. During recomposition, BMI may fall, stay similar or rise. Even when it changes, it cannot tell you which tissue changed. Compare it with body measurements and training progress. ### What is more important for body recomposition: BMI or body fat %? Body-fat estimates add information that BMI cannot provide, but neither proves recomposition. Review body-fat estimates alongside weight, waist and training progress, using consistent measurement methods. ### What is a healthy BMI range for body composition? The WHO healthy range is 18.5–24.9. But body composition research consistently shows that two people at the same BMI can have body fat percentages 10 or more points apart. An active individual at BMI 26 with 15% body fat carries less metabolic risk than a sedentary individual at BMI 22 with 28% body fat. Recompose with Recomp AI ## BMI cannot separate fat from muscle Recomp AI brings your food log, weight trend and body measurements together. Review them alongside your training progress to decide whether your calorie target needs adjusting. Stable weight alone does not show whether you lost fat or gained muscle. [Download on the App Store](https://apps.apple.com/app/recomp-ai-body-recomposition/id6749103634?pt=127576777&ct=recompai_website&mt=8) [Android waitlist](https://www.recompai.com/auth/sign-up) ## References - [Murphy C, Koehler K. Energy deficiency impairs resistance training gains in lean mass but not strength: A meta-analysis and meta-regression. Scand J Med Sci Sports, 2022;32(1):125-137.](https://pubmed.ncbi.nlm.nih.gov/34623696/) - [Antonio J, Ellerbroek A, et al. A high protein diet (3.4 g/kg/d) combined with a heavy resistance training program improves body composition in healthy trained men and women: a follow-up investigation. J Int Soc Sports Nutr, 2015;12:39.](https://doi.org/10.1186/s12970-015-0100-0) - [WHO Consultation on Obesity. Obesity: preventing and managing the global epidemic. WHO Technical Report Series 894, Geneva, 2000. (Source of the adult BMI categories.)](https://iris.who.int/handle/10665/42330) - [Global BMI Mortality Collaboration. Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents. Lancet, 2016;388:776-86.](https://pubmed.ncbi.nlm.nih.gov/27423262/) - [Berrington de Gonzalez A, Hartge P, et al. Body-mass index and mortality among 1.46 million white adults. N Engl J Med, 2010.](https://pubmed.ncbi.nlm.nih.gov/21121834/) - [Romero-Corral A, Somers VK, et al. Accuracy of body mass index in diagnosing obesity in the adult general population. Int J Obes, 2008.](https://pubmed.ncbi.nlm.nih.gov/18283284/) ## Related calculators [Body Fat Calculator Estimate the fat share of body weight and track it alongside other signals.](https://www.recompai.com/tools/bodyfat) [TDEE Calculator Daily calorie needs from your weight and activity level.](https://www.recompai.com/tools/tdee) [How to read your BMI Move from a WHO category to a body composition plan you can act on the same day.](https://www.recompai.com/resources/bmi-body-composition) [Body recomposition calculator Estimate maintenance, a calorie and protein target, and a 12-week fat and lean-mass projection. Results depend on the model assumptions and your response.](https://www.recompai.com/body-recomposition-calculator) ## Related - [All calculators](https://www.recompai.com/tools) - [Body Recomposition Calculator: Calories, Macros, Timeline](https://www.recompai.com/body-recomposition-calculator) - [Body Recomposition: Lose Fat and Build Muscle at Once](https://www.recompai.com/body-recomposition) ## Where to look next - [Home](https://www.recompai.com/) - [All calculators](https://www.recompai.com/tools) - [All guides](https://www.recompai.com/resources) - [Contact](https://www.recompai.com/contact) (recompaiapp@gmail.com) - [Download on the App Store](https://apps.apple.com/app/recomp-ai-body-recomposition/id6749103634?pt=127576777&ct=recompai_website&mt=8) - [llms.txt. A map of this site for agents.](https://www.recompai.com/llms.txt) - [llms-full.txt. The expanded reference.](https://www.recompai.com/llms-full.txt) - [sitemap.xml. 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