+ Health Guide

Health & Body Metrics Calculation Guide

How body mass index, basal metabolic rate, and hydration numbers are calculated.

18 free calculatorsFormula includedWorked example

📚 Overview

Quantitative health metrics provide objective benchmarks to monitor your fitness, nutritional needs, and wellness progress. From daily calorie expenditure to body mass screening, mathematical health formulas give you a data-driven foundation to guide lifestyle decisions.

📐 Body Mass Index (BMI) & Mifflin-St Jeor BMR Equation

BMI = weight(kg) / height(m)^2 and BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age + s

For BMR, s = +5 for biological males and s = -161 for biological females. Total Daily Energy Expenditure (TDEE) is then calculated by multiplying BMR by an activity factor (1.2 to 1.9).

🔢 Worked Example

Scenario: A 32-year-old male weighing 80 kg and measuring 180 cm tall calculating his baseline BMR.

Weight: 80 kg
Height: 180 cm
Age: 32 years
Gender constant s: +5

Weight portion = 10 × 80 = 800
Height portion = 6.25 × 180 = 1,125
Age portion = 5 × 32 = 160
BMR = 800 + 1,125 - 160 + 5 = 1,770 calories/day

His resting body burns 1,770 calories daily. With moderate exercise (multiplier 1.55), his maintenance TDEE is approximately 2,743 calories.

💡 Pro Tips

BMI is a population screening tool, not a diagnostic measure of body fat percentage; muscular athletes may register as overweight.
For healthy weight loss, target a moderate calorie deficit of 300 to 500 kcal per day to preserve lean muscle tissue.
Track body weight first thing in the morning under consistent conditions to minimize water retention fluctuations.
Hydration requirements increase with ambient temperature, humidity, and intense cardiovascular exercise.