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.

  • 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.
  • 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.
  • BMI Calculator
    Calculate your BMI in seconds. Enter height and weight in metric or imperial units to get your body mass index and weight category instantly.
  • 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.
  • 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).
  • 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 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Dog Ideal Weight Calculator
    Estimate your dog's ideal body weight from its current weight and Body Condition Score (1-9). See how much weight to lose or gain for a healthy target.
  • 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).
  • FFMI Calculator
    Calculate your Fat-Free Mass Index (FFMI) and height-adjusted FFMI from weight, height, and body fat percentage to gauge muscle mass.
  • Wilks Calculator
    Calculate your Wilks score from bodyweight and total lifted (kg). Uses the original Wilks coefficient formula for fair powerlifting comparison.

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.

Categories