One-Rep Max Calculator
This tool provides multiple validated estimators for a one-repetition maximum (1RM) based on a performed submaximal set. Estimators are statistical approximations; use them for planning and tracking rather than as replacements for supervised maximal testing.
Choose the formula that best matches your context (lower rep ranges tend to produce more reliable estimates). Always prioritize safety: do not attempt maximal lifts without a trained spotter or proper supervision.
Simple linear-based estimator commonly used for small rep ranges.
Inputs
Results
Estimated 1RM (Epley)
116.6667
| Output | Value | Unit |
|---|---|---|
| Estimated 1RM (Epley) | 116.6667 | kg|lb |
Visualization
Methodology
Multiple published formulas are provided because no single equation is universally accurate across all exercises, rep ranges, or populations. Each formula is derived from regression or curve-fitting against empirical 1RM test data.
To maintain trust and reproducibility we (1) expose several common formulas, (2) show concise expressions so you can compare results, and (3) recommend validation for your specific population or exercise before relying on estimates for program decisions.
Worked examples
Example 1: 100 kg for 5 reps → Epley estimates 100*(1+5/30) = 116.67 kg.
Example 2: 225 lb for 3 reps → Brzycki estimates 225*(36/(37-3)) = 264.7 lb.
Key takeaways
Use lower-rep submaximal sets (1–6 reps) for the most reliable 1RM estimates. For higher reps variance increases and different formulas diverge.
These are estimates — treat them as planning tools and combine them with real-world feedback (bar speed, technique, perceived exertion).
Further resources
External guidance
Expert Q&A
How accurate are these estimators?
Accuracy depends on the exercise, the lifter population, and the rep range. Typical error can be several percent; accuracy declines with higher rep counts. Use these as approximations and validate against supervised maximal testing if precise values are required.
Which formula should I use?
For low reps (1–6) Epley or Brzycki are commonly used. For broader rep ranges consider nonlinear fits (Mayhew/Wathan). When in doubt, compute multiple estimators and use the spread as an uncertainty check.
Are there safety or regulatory considerations?
Yes. Follow workplace and training safety standards when attempting maximal or near-maximal lifts. Use spotters, proper equipment, and adhere to local occupational safety guidance.
How should I account for measurement uncertainty?
Record repeated measurements when possible and use the variance to quantify uncertainty. Apply conservative rounding or a safety buffer when programming based on estimated 1RM.
Can I convert between kg and lb here?
Select your preferred unit in the Units field before entering weight. All formulas are unit-consistent: enter weight in the chosen unit and the output will be expressed in the same unit.
Sources & citations
- National Institute of Standards and Technology (NIST) — https://www.nist.gov
- International Organization for Standardization (ISO) — https://www.iso.org
- Institute of Electrical and Electronics Engineers (IEEE) — https://www.ieee.org
- Occupational Safety and Health Administration (OSHA) — https://www.osha.gov