Free Fitness Calculators for Body Fat, Calories & Health

Free FatCals provides free, science-backed fitness calculators to help you understand your body, track your health metrics, and reach your goals. All 12 tools use validated medical formulas — no sign-up, no paywalls, no ads in your results. Click any calculator to get started instantly.

Body Composition

Know your starting point. These calculators measure how your body is made up — fat vs. muscle, size vs. weight — giving you the foundation for every fitness goal.

• Body Fat Calculator — Calculate your body fat percentage with the scientifically validated U.S. Navy circumference method. Get your body fat %, lean mass, fat mass, and health category.
• BMI Calculator — Calculate your Body Mass Index using height and weight. See whether you're underweight, normal, overweight, or obese per WHO standards.
• Lean Body Mass Calculator — Calculate your lean body mass — the weight of everything except fat, including muscle, bone, water, and organs.
• Ideal Weight Calculator — Find your ideal body weight range using four validated formulas (Devine, Robinson, Miller, Hamwi) plus a BMI-based range.
• Waist-to-Hip Ratio Calculator — Measure your waist-to-hip ratio to assess cardiovascular disease risk — more accurate than BMI for many people.

Calorie & Energy

Understand your body's calorie needs at rest and during activity, then build a precise plan to lose, maintain, or gain weight based on your exact metabolism.

• Calorie Calculator — Find out exactly how many calories you need each day based on your age, height, weight, and activity level using the Mifflin-St Jeor equation.
• TDEE Calculator — Calculate your Total Daily Energy Expenditure — the total calories your body burns each day including all activity.
• BMR Calculator — Calculate your Basal Metabolic Rate — the calories your body needs just to stay alive at complete rest.

Nutrition & Hydration

Fuel your body right. These calculators break down your optimal daily protein, macro split, and hydration targets so your diet supports your training.

• Protein Calculator — Calculate your optimal daily protein intake based on body weight, activity level, and fitness goal.
• Water Intake Calculator — Find out exactly how much water you should drink each day based on your body weight, exercise intensity, and climate.
• Macro Calculator — Calculate your optimal daily macronutrient breakdown — protein, carbohydrates, and fats — based on your calorie target and fitness goal.

Weight Management

Plan your weight loss or maintenance journey with a realistic calorie deficit, timeline, and weekly targets based on your goal and current stats.

• Weight Loss Calculator — Set your goal weight and target date, and get a precise daily calorie deficit plan that's safe and sustainable.

All calculators use peer-reviewed, clinically validated formulas — the same ones used by medical professionals, the U.S. military, and sports scientists. All calculations run entirely in your browser. We never collect personal data, require accounts, or sell information.