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.
Governance
Record 00b9e4b92863 • Reviewed by Fidamen Standards Committee
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.
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).
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.
F.A.Q.
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
- CDC — Body Mass Index (BMI) Categories — https://www.cdc.gov/bmi/adult-calculator/bmi-categories.html
- NIH — National Institutes of Health Metabolic Research — https://www.nih.gov/
- ACSM — American College of Sports Medicine Guidelines — https://www.acsm.org/
- PubMed — Mifflin-St Jeor Equation (PMID: 2305711) — https://pubmed.ncbi.nlm.nih.gov/2305711/
Further resources
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
Record ID: 00b9e4b92863What changed (latest)
v1.0.0 • 2025-11-14 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Public QA status
PASS — golden 25 + edge 120
Last run: 2026-01-23 • Run: golden-edge-2026-01-23
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
What changed (latest)
v1.0.0 • 2025-11-14 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Public QA status
PASS — golden 25 + edge 120
Last run: 2026-01-23 • Run: golden-edge-2026-01-23
Engine
v1.0.0
Data
Baseline (no external datasets)
Content
v1.0.0
UI
v1.0.0
Governance
Last updated: Nov 14, 2025
Reviewed by: Fidamen Standards Committee (Review board)
Credentials: Internal QA
Risk level: low
Reviewer profile (entity)
Fidamen Standards Committee
Review board
Internal QA
Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person
Semantic versioning
- MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
- MINOR: New features or fields that do not change existing outputs for the same inputs.
- PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.
Review protocol
- Verify formulas and unit definitions against primary standards or datasets.
- Run golden-case regression suite and edge-case suite.
- Record reviewer sign-off with credentials and scope.
- Document assumptions, limitations, and jurisdiction applicability.
Assumptions & limitations
- Uses exact unit definitions from the Fidamen conversion library.
- Internal calculations use double precision; display rounding follows the unit's configured decimal places.
- Not a substitute for calibrated instruments in regulated contexts.
- Jurisdiction-specific rules may require official guidance.
Change log
v1.0.0 • 2025-11-14 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: 724398cec672