About

Last updated: 2026-06-25

What is FitCalc

FitCalc is a free set of tools that helps everyone, from complete beginners to dedicated lifters, handle common fitness and training calculations quickly and accurately. It covers 1RM estimation, workout calories burned, body composition (InBody) interpretation, and macro (carbs/protein/fat) splits, presenting seemingly complex math alongside the formulas so anyone can follow.

Operating principles (E-E-A-T)

• Experience — We mirror the same item structure used on real gym result sheets and training programs (1RM, %1RM, skeletal muscle mass, body fat percentage, macros) to break down your results.
• Expertise — We calculate using widely accepted standards: the Epley and Brzycki 1RM formulas, MET-based calorie formulas, standard body fat ranges, and per-nutrient calories (carbs/protein 4 kcal, fat 9 kcal).
• Authoritativeness — We reference formulas and guidelines commonly used in exercise physiology and sports science, and show each calculator's equation.
• Trustworthiness — We never hide the math; we publish it and clearly flag which figures are estimates and any safety cautions. Your inputs are never collected or stored.

Formulas and data we use

The formulas and standards used in each calculator are listed below. Recommended standard values are general guidelines and can vary by individual.

• 1RM — Epley (weight x (1 + reps/30)), Brzycki (weight x 36 / (37 - reps)), and the average of the two.
• Workout calories — Calories = MET x body weight (kg) x time (hours). Per-activity METs reference standard physical-activity MET tables.
• Body composition — Fat mass = weight x body fat percentage; fat-free mass = weight - fat mass. Standard body fat is 10-20% (male) and 18-28% (female).
• Macros — Protein in grams per kg, fat as a ratio of total calories (min 0.8 g/kg), and the rest assigned to carbs. Carbs/protein 4 kcal/g, fat 9 kcal/g.

A note on accuracy and safety

Every FitCalc result is a reference estimate based on your inputs and published formulas. A 1RM is an estimate that may differ from your true max, and workout calories are estimates based on average METs. Body composition interpretation follows general standard ranges, and heavy lifting carries an injury risk, so warming up and using a spotter are recommended. Always consult a qualified trainer or medical professional for final decisions on health, nutrition, and exercise prescription.

Contact

Send suggestions or report errors to jin@zerolabskorea.com. For data handling, see our Privacy Policy.

Last updated: 2026-06-25