Body Composition Calculator

These calculators help you understand how your body is put together — from your BMI and Ideal Body Weight to more nuanced measures like Waist-to-Hip Ratio and BMI Prime. The Reverse BMI Calculator lets you work backwards from a goal weight, while the Adjusted Body Weight Calculator supports clinical and dietitian use cases. Dedicated tools for pets, including the Cat BMI Calculator and Dog BMI Calculator, round out the collection.

Browse the most-popular list to see which tools other visitors reach for first, or open the Trending tab to catch what's gaining attention. Every calculator here is completely free, needs no sign-up, and works on any smartphone, tablet, or desktop browser.

  • Body Fat Percentage Calculator (BMI Method)
    Estimate body fat percentage from your BMI, age and sex using the Deurenberg equation. Free calculator with fat mass and lean mass output.
  • Creatinine Clearance (IBW) Calculator
    Estimate creatinine clearance (CrCl) with the Cockcroft-Gault equation using age, weight, sex, and serum creatinine. Result in mL/min for renal dosing.
  • Daily Protein Requirement Calculator
    Calculate your daily protein needs in grams from body weight and activity level, from the 0.8 g/kg RDA up to 2.2 g/kg for athletes.
  • Devine Ideal Body Weight Calculator
    Calculate ideal body weight with the Devine formula. Enter gender and height in feet/inches to get IBW in kilograms and pounds instantly.
  • BMI Calculator
    Free BMI calculator: enter weight in kg and height in cm to instantly find your Body Mass Index and weight category (underweight, normal, overweight, obese).
  • Target Weight for BMI Calculator
    Find the body weight needed to reach a target BMI. Enter your height, current weight and goal BMI to see your target weight and how much to lose or gain.
  • Fat Mass to Lose for Goal Body Fat % Calculator
    Find how many kg of fat you need to lose to hit a target body fat percentage, assuming lean mass stays constant. Free, instant results.
  • Goal Weight from Body Fat % Calculator
    Calculate your target weight from a goal body fat percentage. Enter current weight, current and target body fat % to find lean mass and goal weight.
  • BMR Calculator (Mifflin-St Jeor)
    Calculate your Basal Metabolic Rate with the Mifflin-St Jeor equation. Enter weight, height, age and gender to find daily resting calories and TDEE.
  • Macro Calculator
    Free macro calculator: convert your daily calories and macro split (%) into grams of protein, carbs, and fat per day using 4/4/9 kcal-per-gram.
  • Katch-McArdle BMR Calculator
    Calculate your Basal Metabolic Rate with the Katch-McArdle formula using lean body mass and body fat percentage. Free, accurate BMR estimate.
  • Waist Circumference Percentile Calculator
    Check your abdominal-obesity health risk from waist circumference. Men >102cm/40in and women >88cm/35in flag high risk. Free, instant, cm or inches.
  • Body Fat % to Lean & Fat Mass Calculator
    Convert your body fat percentage and weight into fat mass and lean body mass instantly. Works with kg or lb — simple, accurate, and free.
  • Body Fat Mass & Fat-Free Mass Calculator
    Calculate your body fat mass and fat-free (lean) mass from your weight and body fat percentage. Fast, free, and works in kg.
  • Army BMI Calculator (AR 600-9)
    Calculate your Body Mass Index using the US Army AR 600-9 method. Enter weight in pounds and height in inches for an instant BMI and category.
  • Goal Weight at Target Body Fat Calculator
    Find your goal weight for a target body fat percentage. Enter current weight and body fat to see how much you'd weigh while preserving lean mass.
  • Army Body Fat Calculator (US)
    Estimate body fat with the US Army AR 600-9 ABCP tape method. Enter height, neck, abdomen (men) or waist & hip (women) in inches.
  • Army Height and Weight Calculator (AR 600-9 Screening)
    US Army AR 600-9 height and weight calculator. Check if your weight is within the screening limit for your height, age, and sex, and see your margin.
  • Body Surface Area Calculator
    Calculate Body Surface Area (BSA) in m² using the Mosteller and Du Bois formulas from your height (cm) and weight (kg). Fast, accurate, free.
  • Goal Body Fat Weight Calculator
    Find your goal weight at a target body fat percentage. Enter current weight and body fat % to see goal weight, fat to lose, and lean mass.
  • RFM (Relative Fat Mass) Calculator
    Estimate your body fat percentage with the RFM (Relative Fat Mass) calculator using only height and waist circumference. Free, fast, and accurate.
  • Body Surface Area (Mosteller) Calculator
    Calculate Body Surface Area (BSA) using the Mosteller formula from height (cm) and weight (kg). Fast, accurate result in square meters (m²).
  • BMI Calculator (Body Mass Index)
    Free BMI calculator. Enter your weight in kg and height in cm to find your Body Mass Index and weight category instantly using the standard WHO formula.
  • Weight Loss Goal Date Calculator
    Find out how many weeks and what date you'll hit your goal weight based on your daily calorie deficit. Free, fast weight loss timeline calculator.

Frequently asked questions

What can I measure with these calculators?

You can assess general weight classification with the BMI Calculator, estimate a healthy target weight with the Ideal Body Weight Calculator, gauge abdominal fat distribution with the Waist-to-Hip Ratio Calculator, and see how your BMI compares to an optimal threshold using the BMI Prime Calculator. Pet-specific tools are also available for cats and dogs.

How accurate are the results?

All tools apply established formulas — for example, the Devine or Robinson formulas for Ideal Body Weight and standard WHO BMI thresholds. Results are population-based estimates, not clinical measurements. These calculators are NOT a substitute for medical advice; consult a qualified healthcare professional before making any health-related decisions.

Do you store or share the measurements I enter?

No. Every calculation runs entirely in your browser. No height, weight, waist, or hip measurements are sent to our servers or retained anywhere. Simply refresh the page to clear all inputs.

Which body composition calculators are most popular?

The list on this page is ranked by real visitor usage, so the top entries reflect what people find most useful day to day. Open the Trending tab to see which tools have seen the biggest recent jump in traffic, or Recently Added for the latest arrivals.

Is it free, and do I need an account?

Completely free — no sign-up, no subscription, and no paywall on results. Every tool works on any modern phone, tablet, or desktop, with no app download required.

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