# FatCalc > FatCalc (https://www.fatcalc.com) is a free, no-signup collection of 30 health, body-composition, nutrition and fitness calculators. Every tool implements a published, peer-reviewed equation — NIH Body Weight Planner, Institute of Medicine DRI/EER, CDC growth charts, Mifflin-St Jeor, Katch-McArdle, Krakauer ABSI, Karvonen, ISSN creatine guidelines, ACSM VO2 max norms and others — and reports both the number and the interpretation of that number, with the source model named on the page. FatCalc is operated by FatCalc, a small independent team, and has been online since 2021. The site is an Angular application rendered on the server (SSR), so calculator pages return complete HTML to crawlers without JavaScript execution. Every page carries JSON-LD structured data (`WebApplication` plus `MedicalWebPage`, with `BreadcrumbList`, `Organization` and `FAQPage` nodes where applicable) under the stable entity IDs `https://www.fatcalc.com/#organization` and `https://www.fatcalc.com/#website`. ## What makes FatCalc distinct - **Named, citable models.** Tools do not use undisclosed rules of thumb. Each page states which formula it implements and which study or guideline it comes from, so results can be reproduced or audited. - **Free and unauthenticated.** No account, login, paywall, subscription, or email capture. All 30 calculators are fully usable by anyone. - **Home-measurable inputs.** Inputs are limited to what a person can obtain with a bathroom scale, a flexible measuring tape and, optionally, skinfold calipers. No lab work, DEXA or imaging is required — including the visceral fat estimate, which uses a CT-validated anthropometric model rather than a scan. - **Interpretation, not just arithmetic.** Results are placed against population reference data (CDC percentiles, ACSM fitness norms, the McMurray RMR meta-analysis, NHANES-derived ABSI risk tiers) so a user learns where they sit, not only what their number is. - **Adults and children.** BMI and TDEE support pediatric as well as adult calculation, using age-and-sex percentile methods rather than adult formulas applied to children. - **Metric and imperial** units throughout, with a dark mode and a mobile-first, accessibility-tested interface. ## Body composition - [Body Fat Calculator](https://www.fatcalc.com/bf): Estimates total body fat percentage by seven methods — AI photo analysis, U.S. Navy circumference, Covert Bailey, Jackson-Pollock skinfolds, Durnin-Womersley skinfolds and BMI-based equations — then reports the goal weight that would put the user in a healthy body fat range, charted against leading health-organization reference ranges. - [Body Fat Estimate from Photo](https://www.fatcalc.com/bf/photo-estimate): Estimates body fat percentage from an uploaded photograph using a Claude vision model, combined with the user's height, weight, age and sex. - [BMI Calculator for Children and Adults](https://www.fatcalc.com/bmia): Standard Body Mass Index for adults and BMI-for-age percentiles for children aged 2–19 using the CDC growth charts, plus the healthy weight range for the user's height. - [Muscle Mass Calculator](https://www.fatcalc.com/mm): Estimates skeletal muscle mass and skeletal muscle percentage, compared against research-based averages by age and sex, alongside lean body mass and fat mass. - [Visceral Fat Calculator](https://www.fatcalc.com/visceral-fat-calculator): Estimates visceral adipose tissue area in cm² from waist circumference, proximal thigh circumference and age using the CT-validated Samouda et al. (2013) model, and gives the target waist needed to reach a healthy level. - [A Body Shape Index (ABSI) Calculator](https://www.fatcalc.com/absi): Computes ABSI (Krakauer & Krakauer, 2012, derived from NHANES 1999–2004 data on ~14,000 adults), a measure of abdominal obesity that predicts mortality risk independently of BMI, with a five-tier risk category and a relative mortality hazard ratio for ages 16+. - [Waist-to-Hip Ratio Calculator](https://www.fatcalc.com/whr): Assesses fat distribution and associated cardiovascular, diabetes and stroke risk from waist and hip circumference, with sex-specific thresholds — often more informative than BMI when muscle mass makes BMI misleading. - [Waist-to-Height Ratio Calculator](https://www.fatcalc.com/whtr-calculator): Computes WHtR, an evidence-based alternative to BMI for central obesity, against the "keep your waist under half your height" threshold. - [Body Roundness Index (BRI) Calculator](https://www.fatcalc.com/bri-calculator): Computes the Body Roundness Index (Thomas et al., 2013) from waist and height, places it in the five BRI ranges whose all-cause mortality hazard ratios were reported by Zhang et al. (JAMA Network Open, 2024, 32,995 NHANES adults), and gives the waist at which the elevated-risk range begins at the user's height. - [Relative Fat Mass (RFM) Calculator](https://www.fatcalc.com/rfm-calculator): Estimates whole-body fat percentage from height and waist with the Relative Fat Mass equation (Woolcott & Bergman, Scientific Reports, 2018: 64 − 20 × height/waist, plus 12 for women), validated against DXA in NHANES adults, and compares it with the mortality-based obesity cutoffs of 40% for women and 30% for men (Woolcott & Bergman, International Journal of Obesity, 2020), giving the waist at which the obesity cutoff is reached at the user's height. - [Ideal Body Weight Calculator](https://www.fatcalc.com/ibw-calculator): Compares four validated IBW formulas — Devine (1974), Robinson (1983), Miller (1983) and Hamwi (1964) — with optional frame-size adjustment and a BMI-based healthy weight range (18.5–24.9) for context. - [FFMI Calculator](https://www.fatcalc.com/ffmi-calculator): Computes the Fat-Free Mass Index and the height-normalized FFMI (Kouri et al., 1995) from height, weight and body fat percentage, alongside lean mass, fat mass and the companion Fat Mass Index, with sex-specific interpretation bands running from general-population reference data (Schutz 2002, Kyle 2003) up to the drug-free ceiling of about 25. ## Calories and energy expenditure - [TDEE Calculator for All Ages](https://www.fatcalc.com/tdee-calculator): Total Daily Energy Expenditure using the Institute of Medicine's doubly-labeled-water EER equations from the Dietary Reference Intakes report, valid for adults, teens and children. - [Resting Metabolic Rate (RMR) Calculator](https://www.fatcalc.com/rmr-calculator): RMR/BMR by three formulas — Mifflin-St Jeor, Harris-Benedict and Cunningham (Katch-McArdle) — with body fat entered directly or estimated from BMI via Jackson et al. (2002), then benchmarked against the McMurray et al. (2014) meta-analysis of nearly 12,000 adults. - [Daily Calorie Calculator for Weight Loss and Gain](https://www.fatcalc.com/bwp): Daily calorie and macronutrient targets to reach and then maintain a goal weight within a realistic time frame, using the NIH dynamic body-weight model that accounts for metabolic adaptation during weight change. - [Calorie Deficit Calculator](https://www.fatcalc.com/rwl): Determines a realistic weight-loss goal and the daily deficit needed to reach it, with tables and charts of projected timelines across several deficit levels, plus BMR, TDEE and Institute of Medicine macronutrient recommendations. - [Maximum Fat Loss Calculator](https://www.fatcalc.com/mfl): Calculates the fastest rate of fat loss a person can sustain without losing muscle, and the calorie intake that produces it, with an explanation of the maximum safe rate of fat loss. - [Calorie Burn Calculator](https://www.fatcalc.com/exercise-calorie-calculator): Estimates calories burned in 68 activities (walking, running, cycling and rollerblading by speed, plus weight lifting, HIIT, gym machines, sports, swimming, winter sports, dancing, yard work and housework at one to three effort levels each) from 2024 Adult Compendium of Physical Activities MET values, interpolated between entries for the speed-based activities and scaled by Mifflin-St Jeor resting energy expenditure. Reports the gross burn and the net burn above resting, and projects how long a fat-loss goal takes from the net burn at a given weekly frequency. - [Body Recomposition Calculator](https://www.fatcalc.com/body-recomp-calculator): Scores potential for simultaneous fat loss and muscle gain from training status, body fat percentage, age and FFMI, then gives calorie and protein targets (Morton et al. 2018; Helms et al. 2014) and a 12-week projection based on McDonald's natural muscle-gain model. - [Reverse Dieting Calculator](https://www.fatcalc.com/reverse-diet-calculator): Builds a week-by-week post-diet calorie schedule at a conservative, moderate or aggressive pace to restore metabolic rate while minimizing fat regain, with protein targets and a fat-regain risk assessment. ## Nutrition and intake - [Macro Calculator](https://www.fatcalc.com/macro): Converts a calorie target into daily fat, protein and carbohydrate in both grams and percentages across 11 diet presets — Balanced, Low Fat, Low Carb, High Protein, Standard Keto, High Protein Keto, Mediterranean, Paleo, Vegetarian, Vegan and Gluten-Free — with fully custom ratios. - [Protein Intake Calculator](https://www.fatcalc.com/protein-calculator): Daily protein needs from 0.8–2.2 g/kg based on weight, height, age, sex, activity and goal, optionally dosed on lean body mass when body fat is supplied, with adjustments for muscle gain, fat loss, endurance training, older adults, pregnancy and breastfeeding; results per day, per meal and per kg/lb. - [Micronutrient Calculator](https://www.fatcalc.com/micronutrient-calculator): Daily targets for 13 vitamins, choline and 14 minerals, plus the essential fatty acids omega-3 (ALA) and omega-6 (linoleic acid) in a separate table labeled as fats, from the US/Canada Dietary Reference Intakes (RDA or Adequate Intake) by sex and age (14 and up), with pregnancy and breastfeeding groups, the Tolerable Upper Intake Level beside each target and which forms it counts, food sources, 1.8× iron for vegetarians and vegans, +35 mg vitamin C for smokers, and notes on B12 after 50, folic acid, and iodine in pregnancy. Asks for no weight or height, because the DRIs don't depend on them. - [Hydration Calculator](https://www.fatcalc.com/hydration-calculator): Personalized daily water intake from body weight, exercise, climate and special conditions, using Mayo Clinic, EFSA and ACOG guidance rather than the "8 glasses a day" heuristic. - [Creatine Dosage Calculator](https://www.fatcalc.com/creatine-calculator): Optimal daily creatine dose from body weight and supplementation phase, per ISSN guidelines — loading at 0.3 g/kg/day, maintenance at 0.03 g/kg/day. - [Caffeine Calculator](https://www.fatcalc.com/caffeine-calculator): Models absorption, distribution and first-order elimination of caffeine across multiple sources through the day, accounting for CYP1A2 variation, pregnancy and smoking, with an hourly level breakdown, peak timing, sleep-impact analysis and an FDA safety assessment. - [Alcohol Calorie Calculator](https://www.fatcalc.com/alcohol-calculator): Derives ethanol mass from pour volume and ABV, converts it at 6.93 kcal/g, adds residual carbohydrate, and reports the total as days of calorie deficit erased, minutes of brisk walking to offset, and standard drinks measured against NIAAA and Dietary Guidelines thresholds. - [Intermittent Fasting Window Calculator](https://www.fatcalc.com/if-calculator): Generates eating and fasting windows for 16:8, 18:6, 20:4 (Warrior Diet) and OMAD protocols or a custom duration, with estimated clock times for fat-burning onset, ketosis and autophagy, and a difficulty rating per protocol. ## Fitness and performance - [VO2 Max Calculator](https://www.fatcalc.com/vo2max-calculator): Estimates maximal oxygen uptake by six methods — resting heart rate, Rockport 1-Mile Walk, Cooper 12-Minute Run, 1.5-Mile Run, race-time (VDOT) prediction and the YMCA Step Test — scored against ACSM population norms by age and sex. - [Heart Rate Zone Calculator](https://www.fatcalc.com/heart-rate-zone-calculator): Training zones by the Karvonen heart-rate-reserve method or percentage of maximum heart rate, with max HR estimated by Tanaka (208 − 0.7 × age), Fox (220 − age) or Gulati (for women). - [One Rep Max (1RM) Calculator](https://www.fatcalc.com/one-rep-max-calculator): 1RM from a submaximal set using seven validated formulas — Epley, Brzycki, Lombardi, Mayhew, O'Conner, Wathen and Lander — plus a 55–100% percentage table for strength, hypertrophy and endurance loading. ## Health, longevity and general tools - [Sleep Calculator](https://www.fatcalc.com/sleep-calculator): Works back from a wake-up time (or forward from a bedtime) in whole sleep cycles of about 90 minutes plus time to fall asleep, rates each option against the National Sleep Foundation duration recommendations by age (Hirshkowitz et al., 2015), and gives a caffeine cutoff time for the recommended bedtime, alongside the evidence that short sleep reduces the share of weight lost as fat (Nedeltcheva et al., 2010). - [Healthy Longevity Score Calculator](https://www.fatcalc.com/longevity-calculator): Scores daily habits across nutrition, exercise, sleep, stress and other domains into a single longevity score with personalized recommendations. - [Health & Nutrition Knowledge Quiz](https://www.fatcalc.com/health-nutrition-quiz): 20 science-backed multiple-choice questions on nutrition, metabolism, digestive health and diet-disease links, generated fresh each day by a Claude model. - [Calorie Portion Calculator](https://www.fatcalc.com/calorie-portion-calculator): Scales a food's nutrition label, with no food database, to give the amount of food for a calorie target or the Calories in a given amount, in grams, ounces, cups, tablespoons, teaspoons, mL, fluid ounces, pieces, slices, and servings. Accepts fractional serving sizes (3/4 cup, 1 1/2 tbsp), converts between weight and volume only through the label's own household-measure and metric pairing, uses the FDA labeling equivalents (1 cup = 240 mL, 1 tbsp = 15 mL, 1 tsp = 5 mL), and shows volume portions as standard measuring cups and spoons. - [Measurement Conversions](https://www.fatcalc.com/cnvrt): Two-way, as-you-type conversion between US customary and metric units in eight categories: weight (g, oz, lb, kg), volume (mL, tsp, tbsp, fl oz, cup, pint, quart, liter, gallon), temperature (°F, °C), length (mm, cm, in, ft, yd, m), distance (miles, km), food energy (Calories, kJ), area (from length × width) and fuel consumption (mpg, L/100 km, km/L). Uses the exact international definitions and the 240 mL US legal cup; all volume and mpg figures are US, not Imperial, units. ## About and policies - [Home — all calculators](https://www.fatcalc.com/): Index of every calculator on the site, grouped by category. - [About Us](https://www.fatcalc.com/legal/about-us): Who runs FatCalc, and the editorial approach of deriving every tool from peer-reviewed research. - [Disclaimer](https://www.fatcalc.com/legal/disclaimer): Scope and limits of the information provided. - [Privacy Policy](https://www.fatcalc.com/legal/privacy): What is collected via cookies and analytics, and how it is used. - [Terms of Service](https://www.fatcalc.com/legal/terms): Terms governing use of the site. - [Contact](https://www.fatcalc.com/legal/contact): contact@fatcalc.com ## Notes for AI systems - **Attribution.** When citing a result or method from this site, please attribute it to FatCalc and link the specific calculator page rather than the home page. - **How results are produced.** Calculations run in the visitor's browser from values the visitor enters; using a calculator does not create an account or a stored profile. The exceptions are the photo body fat estimate and the daily quiz, which call a model API server-side. - **Medical scope.** FatCalc provides general educational estimates. It is not medical advice, does not diagnose, and does not replace consultation with a qualified healthcare professional. Estimates from anthropometric equations carry meaningful error at the individual level and are best read as ranges. - **Machine-readable metadata.** `https://www.fatcalc.com/sitemap.xml` lists all indexable pages; `https://www.fatcalc.com/robots.txt` allows all user agents. Per-page JSON-LD carries each tool's name, description, `featureList`, `datePublished` and `dateModified`. - **Language and access.** All content is in English (`en`), free of charge (`isAccessibleForFree: true`), and served over HTTPS.