About RepWorks

RepWorks is a collection of free fitness calculators for everyone — whatever and however you train. Every tool is built around a question people actually ask during a workout — what pace, what heart rate, what weight, which plates — and answers it in seconds, on any device, with the formula shown so you can verify the math yourself.

The calculators

• Pace Calculator — Calculate your running pace per mile or kilometer for any distance — 5K, 10K, half marathon, or marathon. Get split times and your target finish time instantly.
• Race Time Predictor — Predict your finish time for the 5K, 10K, half marathon, and marathon from a recent race result using the proven Riegel formula.
• Heart Rate Zones — Find your 5 heart rate training zones from your age or measured max heart rate. Supports the Karvonen (heart rate reserve) method with resting heart rate.
• One Rep Max — Estimate your one rep max (1RM) for squat, bench press, deadlift, or any lift from a submaximal set. Uses Epley, Brzycki, Lombardi, and O'Conner formulas with a full percentage table.
• Plate Calculator — Enter a target weight and see exactly which plates to load on each side of the barbell, in pounds or kilograms. Supports standard 45 lb and 20 kg bars.

How it stays free

The site is supported by advertising, which keeps every calculator free with no accounts, no paywalls, and no feature limits.

A note on accuracy

The formulas used here (Riegel, Karvonen, Epley, Brzycki, and others) are the standards used by coaches and exercise scientists, and each tool page documents its method. They are estimates for healthy adults and informational only — not medical or coaching advice.