One-Rep Max Calculator
Estimate your 1RM one-rep max from any set of reps and weight using the Epley formula.
How to use this tool
- Enter weight lifted and reps performed in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your estimated 1rm and the full breakdown beneath it.
The Epley formula estimates your one-repetition maximum from any multi-rep set. Use this to track strength progress without maxing out every session.
⚠ This tool is for general information and education only and is not medical advice. Consult a qualified healthcare professional before making health decisions.
Formula
1RM = Weight × (1 + Reps ÷ 30)
This is the Epley formula (1985), where weight is in any consistent unit (kg or lb) and reps is the number of repetitions completed to near-failure in one set.
How it works
The Epley formula estimates the maximum weight you could lift for a single repetition from a submaximal multi-rep set, assuming each additional rep beyond one represents approximately 3.3% of 1RM (i.e., 1/30 per rep). It is accurate for sets of roughly 2–10 reps; predictive accuracy declines beyond 10 reps as fatigue and endurance factors dominate.
The formula does not account for lift type, bar speed, or individual fatigue curves, so results are estimates. Use them to guide programming percentages rather than as precise load prescriptions.
Worked example
- Weight lifted: 100 kg. Reps performed: 5.
- 1RM = 100 × (1 + 5 ÷ 30) = 100 × (1 + 0.1667) = 100 × 1.1667.
- 1RM = 116.67 kg.
Estimated 1RM: 116.67 kg
Common mistakes to avoid
- Using a set performed far from failure — the Epley formula assumes reps performed to near-failure; a comfortable set of 10 will significantly underestimate actual 1RM.
- Entering reps above 10 or 12: the Epley formula becomes increasingly inaccurate beyond about 10 reps, and most practitioners cap its use there.
- Treating the estimated 1RM as a safe maximal-effort target for an immediate attempt without a proper warm-up progression.
Key terms
- One-Rep Max (1RM)
- The maximum weight that can be lifted for exactly one full repetition with correct technique; the standard benchmark for absolute strength.
- Epley formula
- A 1985 equation by Boyd Epley estimating 1RM as Weight × (1 + Reps/30); one of the most commonly cited submaximal prediction equations.
- Submaximal testing
- Estimating 1RM from a set performed at less than maximum effort, reducing injury risk compared to an actual single-rep max attempt.
- Training percentage
- A load expressed as a fraction of 1RM (e.g. 75% 1RM) used to prescribe intensity for strength and hypertrophy programmes.
Frequently asked questions
- What is the Epley formula?
- Epley 1RM = weight × (1 + reps ÷ 30). It is one of several accepted formulas; accuracy decreases for sets above 10 reps.
- Is the estimated 1RM accurate?
- It is an estimate. Studies show Epley is accurate to within ~5% for sets of 1–10 reps. For very high rep sets (15+) accuracy drops — use sets of 3–8 for best results.