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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19 Calculators

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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

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.

Evidence-based daily protein targets tailored to your goal: maintain, build muscle, or lose fat.

Personalized daily hydration targets adjusted for body weight, activity, and climate.

Caloric Deficit

Find the right caloric deficit to reach your goal weight safely without losing muscle.

One-Rep Max (1RM)

Estimate your maximum lift for any exercise from submaximal sets using validated formulas.

VO₂max Estimator

Estimate your aerobic capacity — the gold standard of cardiovascular fitness.

Compare powerlifting total across different body weights. The standard for fair competition.

Heart Rate Zones

Calculate your 5 training zones for optimal aerobic base, threshold, and VO₂max development.

Ideal Body Weight

Research-based ideal weight ranges by height and frame size, from multiple clinical formulas.

Body Adiposity Index

An alternative to BMI that estimates body fat directly from hip circumference and height.

Macro Calculator

Full protein, carb, and fat targets based on your goal and activity level. ISSN-based recommendations.

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.

Sleep Calculator

Calculate optimal sleep duration and ideal bedtimes based on 90-minute sleep cycles and NSF guidelines.

From the Blog

View all articles →

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

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

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.