Science-Backed · Sources Cited

Health Calculators
That Actually Mean Something

Free Online Fitness, Body Composition & Nutrition Calculators

Every calculator on KineticMetrix is grounded in published research. Get results you can trust, with the science to back them up.

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20 Calculators
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All Calculators

Body Mass Index (BMI)
A weight-to-height ratio used to classify body weight categories from underweight to obese.
Body Composition
Fat-Free Mass Index (FFMI)
A height-normalized measure of muscularity. Widely used to assess natural muscular potential.
Body Composition
Body Fat % (Navy Method)
Estimates body fat percentage using circumference measurements. No calipers needed.
Body Composition
Lean Body Mass
Calculate your total mass minus body fat. Essential for nutrition and training programming.
Body Composition
Waist-to-Hip Ratio
A simple but powerful predictor of cardiovascular and metabolic health risk.
Body Composition
TDEE Calculator
Total Daily Energy Expenditure — how many calories you burn per day based on activity level.
Nutrition
Protein Needs
Evidence-based daily protein targets tailored to your goal: maintain, build muscle, or lose fat.
Nutrition
Water Intake
Personalized daily hydration targets adjusted for body weight, activity, and climate.
Nutrition
Caloric Deficit
Find the right caloric deficit to reach your goal weight safely without losing muscle.
Nutrition
One-Rep Max (1RM)
Estimate your maximum lift for any exercise from submaximal sets using validated formulas.
Performance
VO₂max Estimator
Estimate your aerobic capacity — the gold standard of cardiovascular fitness.
Performance
Wilks Score
Compare powerlifting total across different body weights. The standard for fair competition.
Performance
Heart Rate Zones
Calculate your 5 training zones for optimal aerobic base, threshold, and VO₂max development.
Performance
Ideal Body Weight Calculator
Research-based ideal weight ranges by height and frame size, from multiple clinical formulas.
Longevity
Body Adiposity Index
An alternative to BMI that estimates body fat directly from hip circumference and height.
Longevity
Macro Calculator
Full protein, carb, and fat targets based on your goal and activity level. ISSN-based recommendations.
Nutrition
Visceral Fat Estimator
Estimate deep abdominal fat risk from waist circumference and height. A stronger predictor of disease than BMI.
Body Composition
Running Pace Calculator
Predict race finish times at any distance and calculate training paces using Riegel's formula.
Performance
Sleep Calculator
Calculate optimal sleep duration and ideal bedtimes based on 90-minute sleep cycles and NSF guidelines.
Longevity
Sleep Duration Calculator
Enter when you went to bed and woke up to see how many hours you actually slept, whether you woke mid-cycle, your REM estimate, and how it compares to your age need.
Longevity

From the Blog

View all articles →
Nutrition
TDEE Explained: How Many Calories You Burn Per Day
Total Daily Energy Expenditure: the Mifflin-St Jeor formula, activity multipliers, four-formula comparison, worked examples, and how to verify your real TDEE.
Apr 2026· 15 min read
 Performance
Heart Rate Zones: How to Calculate All 5 Training Zones
Tanaka vs Karvonen, the 80/20 polarised training rule, Zone 2 deep dive, and why most recreational athletes train in the wrong intensity zone.
Apr 2026· 16 min read
 Longevity
How Much Sleep Do You Need? Cycles, Stages & Optimal Duration
NSF age-specific recommendations, the U-shaped mortality curve, NREM/REM cycles, athlete sleep extension research, and how to time bedtime around 90-minute cycles.
Apr 2026· 15 min read

Frequently Asked Questions

Are KineticMetrix calculators free?

Yes. Every calculator on KineticMetrix is free to use, with no account, signup, or subscription required. Revenue comes from display advertising and Amazon affiliate links, not from user fees.

How are the formulas validated?

Every calculator implements a formula from a published source — typically a peer-reviewed journal paper, sometimes a textbook, government report, or expert consensus statement. The original publication is cited on each calculator page in a "Methodology & Sources" section, with DOI or PubMed link where available.

Does KineticMetrix store my data?

No. KineticMetrix has no user accounts, does not log calculator inputs, and does not collect personal information. Inputs are sent to the API only to compute your result and are not retained. See the Privacy Policy for full details.

Are KineticMetrix results medical advice?

No. KineticMetrix calculators provide statistical estimates from published formulas. They are for general informational purposes only and are not medical advice, diagnosis, or treatment. For health-related decisions, consult a qualified healthcare professional.

Why do KineticMetrix calculators sometimes give different results from other sites?

Many online calculators implement formulas without naming the source. KineticMetrix uses validated published formulas (e.g. Mifflin-St Jeor 1990 for BMR, Tanaka 2001 for max heart rate, Morton 2018 for protein) and discloses each one. If two sites disagree, check which formula each is using — different formulas exist for the same metric, and the choice matters.

Who runs KineticMetrix?

KineticMetrix is built and maintained by Andreas Hartenberg, a self-tracker with a long-running interest in evidence-based body composition, training, and recovery. He is not a doctor, dietitian, or coach. See the About page for full background, editorial process, and methodology.