ZenFit.Tools
Gym-Tech Physiological Architecture · 2026 Edition

Elite Health, Nutrition & Biohacking Analytics

Nineteen validated sports medicine, metabolic, and anthropometric calculators. Instant client-side precision, peer-reviewed formulas, and zero server latency.

Instant Client-Side Math
ACSM & ISSN Aligned
Zero Data Harvesting
Evidence-Based Analytics

Explore The 19 Elite Physiological Tools

Select any calculator below to open its dedicated analytics workstation, peer-reviewed formulas, and clinical guidelines.

Showing 19 of 19 Tools
5 min readCore Metric

TDEE & Daily Calorie Burn Calculator

Calculate your precise Total Daily Energy Expenditure (TDEE) and basal metabolic rate using Mifflin-St Jeor and Katch-McArdle equations.

TDEE = BMR × Physical Activity Level (PAL)Calculate
6 min readNutrition Suite

Advanced Macronutrient & Macro Split Estimator

Calculate gram-accurate protein, carbohydrate, and dietary fat ratios tailored to fat loss, muscle hypertrophy, or ketogenic protocols.

Caloric Budget = (Protein × 4 kcal) + (Carbohydrate × 4 kcal) + (Fats × 9 kcal)Calculate
4 min readClinical Anthropometry

US Navy Body Fat Percentage Calculator

Empirical body circumference method adopted by the United States Department of Defense for accurate body composition assessment.

Logarithmic circumference regression modeling height, neck, waist, and hipsCalculate
5 min readPower & Strength

One-Rep Max (1RM) & Strength Standards Calculator

Calculate your maximum single-rep strength using 6 peer-reviewed formulas and view customized percentage-based training loads.

Brzycki, Epley, Lombardi, Mayhew, O'Conner, and Wathan empirical modelsCalculate
4 min readCardiovascular Suite

Target Heart Rate & Training Zones Calculator

Determine your 5 cardiovascular physiological training zones based on Tanaka age-predicted maximum and Karvonen Heart Rate Reserve.

Tanaka Max HR = 208 - (0.7 × Age) | Karvonen Target = Rest HR + [% × (Max HR - Rest HR)]Calculate
4 min readEndurance Science

Running Pace & Race Time Predictor

Convert split paces (min/km & min/mile) and predict 5K, 10K, Half, and Full Marathon times using Pete Riegel’s fatigue equation.

Riegel Fatigue Model: T2 = T1 × (D2 / D1)^1.06Calculate
5 min readCircadian Biology

Intermittent Fasting Window & Autophagy Timer

Plan circadian feeding windows (16:8, 18:6, 20:4, OMAD) and map physiological metabolic checkpoints from ketosis to peak autophagy.

Temporal feeding boundaries & cellular lysosomal autophagy progressionCalculate
3 min readElectrolyte Balance

Daily Water & Hydration Intake Calculator

Calculate volumetric fluid requirements based on body mass, exercise sweat rate, environmental climate, and electrolyte dynamics.

Fluid Requirement = (Body Mass × 35 ml/kg) + Exercise Sweat Loss + Climate AdjustmentCalculate
4 min readErgogenic Aids

Creatine Loading & Dosage Calculator

Calculate optimal creatine monohydrate loading vs steady saturation protocols and daily maintenance doses based on lean body mass.

Loading: 0.3 g/kg/day (divided 4×) for 5-7 days | Maintenance: 0.03-0.05 g/kg/dayCalculate
5 min readNatural Limit Benchmarks

Lean Body Mass (LBM) & FFMI Calculator

Calculate Fat-Free Mass Index (FFMI) and normalized FFMI to evaluate genetic muscle-building limits based on Kouri et al. benchmarks.

FFMI = LBM (kg) / Height (m)² | Normalized = FFMI + 6.1 × (1.8 - Height)Calculate
4 min readAnthropometry

Ideal Body Weight & Bone Frame Size Calculator

Compare Devine, Robinson, Miller, and Hamwi clinical equations with wrist circumference bone frame size calibrations.

Devine, Robinson, Miller, & Hamwi clinical formulas + r-value frame ratioCalculate
6 min readGenetic Limits

Maximum Muscular Potential Estimator

Estimate your genetic ceiling for natural drug-free lean mass and maximum muscle girths using Casey Butt and Martin Berkhan models.

Casey Butt Skeletal Frame Model & Berkhan Leangains EquationCalculate
3 min readCardiometabolic Health

Waist-to-Height Ratio (WHtR) & Health Risk Calculator

Assess deep visceral intra-abdominal adiposity and cardiometabolic risk using the clinically validated Ashwell Shape Chart methodology.

WHtR = Waist Circumference / Height | Target: Keep your waist to less than half your heightCalculate
4 min readEnergy Expenditure

Calories Burned per Exercise Calculator

Calculate exercise energy expenditure for 35+ sports and strength activities using the Compendium of Physical Activities MET database.

Calories = (MET × 3.5 × Body Mass in kg / 200) × Duration in MinutesCalculate
4 min readNeuro-Restoration

Sleep Cycle & Circadian Wake-Up Estimator

Time your sleep and wake alarms in exact 90-minute ultradian cycles to bypass sleep inertia and maximize deep restorative slow-wave sleep.

90-Minute Ultradian Sleep Cycle + 14-Minute Average Sleep LatencyCalculate
5 min readClinical Comparison

Basal Metabolic Rate (BMR) Comparative Calculator

Side-by-side comparative analysis of Mifflin-St Jeor, Revised Harris-Benedict, Katch-McArdle, and Schofield WHO equations.

Comparative matrix across 4 clinical BMR prediction methodologiesCalculate
5 min readAnabolic Optimization

Protein Intake Timing & Distribution Calculator

Optimize Muscle Protein Synthesis (MPS) by calculating per-meal leucine thresholds, meal distribution frequency, and nocturnal micellar casein.

Per-Meal Dose = 0.40 - 0.55 g/kg | Leucine Threshold = 2.7 - 3.2g per bolusCalculate
7 min readBody Recomposition

Body Recomposition & Caloric Surplus/Deficit Planner

Plan concurrent adipose reduction and skeletal muscle hypertrophy with periodized caloric budgeting and high-protein partitioning.

Iso-caloric to Mild Deficit (-10% to 0%) + Protein at 2.2 - 2.6 g/kgCalculate
4 min readCardio Physiology

Heart Rate Reserve (HRR) & Cardio Intensity Zone Calculator

Calculate clinical Karvonen Heart Rate Reserve zones factoring individual resting bradycardia for precision endurance prescription.

Target HR = Resting HR + [% Intensity × (Max HR - Resting HR)]Calculate

Specialized Category Hubs

Browse our curated physiological clusters designed around specific training, metabolic, and biometric goals.

5 Core Calculators

Metabolism & Diet

Validated clinical models for caloric expenditure, adaptive thermogenesis, nutrient partitioning, and fasting physiology.

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5 Precision Models

Body Composition

Anthropometric formulas, logarithmic circumferences, lean mass tracking, and natural muscular thresholds.

Explore Hub Calculators
5 Athletic Tools

Cardio & Strength

Cardiopulmonary reserve metrics, fatigue kinetics, maximal strength standards, and metabolic equivalent expenditure.

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4 Longevity Tools

Biohacking & Recovery

Ultradian sleep architecture, cellular hydration dynamics, cellular ergogenic saturation, and chronobiology.

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Validated Sports Science & Peer-Reviewed Standards

Rigorous clinical formulas derived from ACSM, ISSN, DoD, and PubMed peer reviews

Every tool within ZenFit Tools is engineered from verified empirical literature. From Mifflin-St Jeor metabolic calorimetry and Hodgdon-Beckett logarithmic anthropometry to Casey Butt's muscular potential formulas and Tanaka heart rate kinetics, we eliminate speculative gym-lore in favor of peer-reviewed mathematical certainty.

Read Full Methodology & Citations•Medical & Clinical Disclosures