Strength Calculator
Estimate a one-repetition maximum (1RM) from a completed weight-and-repetition set using the Epley or Brzycki equation, then view simple percentages of that estimate. Results are mathematical training references—not medical advice, a diagnosis, a safety clearance, or an individualized exercise prescription.
Estimate Your 1RM
How the Strength Calculator Works
Both selectable equations estimate 1RM from a load completed for multiple repetitions.
Epley equation
1RM = weight × (1 + reps ÷ 30). A one-repetition input is treated as the lifted weight itself.
Brzycki equation
1RM = weight × 36 ÷ (37 − reps). A one-repetition input is likewise treated as the actual lifted weight.
Why results differ
Prediction equations model the repetitions-to-load relationship differently. Individual endurance, exercise selection and population can affect prediction error, so the selected equation remains visible.
Percentage references
The 50–95% values are arithmetic percentages of the estimated 1RM. They are not automatic set/rep prescriptions or personalized training recommendations.
How Accurate Is an Estimated 1RM?
No single accuracy percentage applies to every person, exercise, repetition range and equation. Published validation studies show that repetition-based equations can estimate 1RM, while prediction error varies across equations and testing conditions.
Research also shows that direct 1RM measurements themselves have test-retest variability. The useful interpretation is therefore estimated 1RM, not an exact physiological maximum.
Strength Calculator Examples
These examples use exactly the equations available above.
185 lb × 5 — Epley
100 kg × 3 — Brzycki
135 lb × 12 — Epley
How to Interpret Percentage-of-1RM Values
The table intentionally avoids labeling fixed percentages as universal “strength,” “hypertrophy,” “fat loss,” or “endurance” zones. Resistance-training outcomes depend on more than load percentage, including volume, exercise selection, range of motion, effort, frequency, experience and recovery.
The percentages are best read as mathematical reference points. Whether a particular load, set, repetition range or program is suitable for an individual is a separate question that this calculator does not answer.
When a Calculator Is Not Enough
This page provides general educational information about strength-estimation mathematics. It does not diagnose an injury, assess cardiovascular risk, determine readiness for exercise, clear a person for maximal lifting, or replace individualized medical advice.
If exercise causes chest pain, fainting, severe shortness of breath, sudden neurological symptoms, or another potentially urgent symptom, stop exercising and seek appropriate medical care rather than relying on a calculator. For non-urgent health concerns or uncertainty about whether resistance training is appropriate for your circumstances, consult an appropriately qualified healthcare professional.
What This Calculator Does Not Tell You
It does not measure a true 1RM
A prediction equation is different from directly testing a maximum and should be described as an estimate.
It does not rank you against other lifters
Strength rankings require a defined comparison dataset, population, exercise standard and methodology. Arbitrary bodyweight tiers are not used here.
It does not prescribe a workout
The percentage table does not account for health status, training history, fatigue, technique, equipment or individual goals.
It does not transfer between exercises
An estimate from one lift should not be treated as the 1RM for another exercise.
Strength Calculator FAQ
What is a one-repetition maximum?
Should I use Epley or Brzycki?
Why is there a warning above 10 repetitions?
Why are there no beginner or elite rankings?
Can I attempt the calculated 1RM?
Related CalcsDone Calculators
Strength Calculator References
- LeSuer et al. — prediction of one-repetition maximum strength — comparison of repetition-based prediction equations.
- Whisenant et al. — submaximal bench-press prediction equations — research on predicting 1RM from repetition performance.
- Grgic et al. — systematic review of 1RM test-retest reliability — context on measurement variability.
- American College of Sports Medicine — 2026 resistance-training position stand — contemporary evidence synthesis for resistance-training prescription.
- CalcsDone Methodology — how formulas, assumptions, limitations and sources are documented.