How our calculators are built, checked and reviewed

1. Define the calculation

Each tool starts with a clearly defined input and output. For 1RM tools, the input is a completed set: load plus repetitions. For percentage tools, the input is a 1RM plus a percentage. Plate tools use a target and bar weight.

2. Use established equations

Our 1RM tools currently show five established prediction equations: Epley, Brzycki, Lander, Lombardi and O’Conner. These equations appear in the published strength literature and are used here as prediction models, not as direct measurements.

3. Reproduce the math

The equation is visible on each applicable page so a reader can reproduce the calculation manually. The site does not hide the calculation behind an unexplained single number.

4. Check edge cases

Inputs outside the supported range are rejected. The 1RM calculators use 1–12 repetitions because prediction error can become more problematic as repetition counts increase and lifters differ in muscular endurance.

5. Review the implementation

Formula transcription, unit handling, rounding, output formatting and page content are reviewed together. When code changes, the calculator is rechecked.

6. Record the review date

Each tool displays a last-reviewed date. A future update should change that date only after the calculation and page have actually been reviewed.

What the formulas cannot do

They cannot account for every individual's technique, range of motion, fatigue, equipment, training history or proximity to failure. A mathematically correct formula can still produce an imperfect estimate when its assumptions do not match the set used as input.