One Rep Max Calculator
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What Your Result Means
- Your One-Rep Max (1RM) is the theoretical maximum weight you can lift for a single clean repetition. It's the standard reference point that strength training programs use to assign training loads across different exercises.
- Epley vs. Brzycki: Both formulas estimate 1RM from submax lifts, but they use different mathematical approaches. Epley is slightly more conservative; Brzycki tends toward higher estimates. This calculator averages both for a more balanced estimate.
- The percentage chart shows recommended weights for different training intensities (50–95% of your 1RM). For example, a 75% 1RM load is typically used for strength-focused work (3–6 reps per set).
- Important caveat: Accuracy decreases significantly above about 10 reps. If you entered a set of 20+ reps, your 1RM estimate is less reliable—consider testing a submax set closer to your max strength limit.
How This Calculator Works
Enter your weight lifted and the number of reps you completed for that weight, then choose your unit (pounds or kilograms). The calculator applies two well-established formulas—Epley and Brzycki—to estimate your one-rep max from that single submax set. It averages the two estimates to reduce bias toward either formula, then generates a complete percentage chart (50–95% of your estimated 1RM) to help you plan working sets across different rep ranges and training goals.
Quick Questions
How accurate is a 1RM estimate?
Accuracy is best for sets of 2–10 reps and can vary by ±5–10% depending on your experience level and lifting technique. Beginners may see wider variation; advanced lifters tend to be more consistent.
Why two formulas?
Epley and Brzycki were developed independently and use different mathematical assumptions. Epley is more conservative and works well for lower rep counts; Brzycki tends to predict slightly higher maxes. Averaging them reduces the risk of significant over- or under-estimation.
What's a good training percentage?
Training intensity depends on your goal. 80–90% is typical for strength work (1–6 reps), 70–80% for hypertrophy (6–12 reps), and 50–70% for endurance and recovery work. Most programs use a mix across different sessions.
Should I test a true 1RM?
Testing a true 1RM is useful for baseline data and motivation, but it's taxing and carries injury risk. Most strength programs rely on estimated 1RMs for daily training and reserve true max testing for occasional checkpoints (every 3–6 months).
Why does accuracy drop above 10 reps?
These formulas were calibrated using data from lower-rep sets where strength (not fatigue or metabolic demand) is the limiting factor. Above 10 reps, fatigue, form breakdown, and individual conditioning become much more variable, reducing the reliability of any single-formula estimate.
Sources
- NSCA — Essentials of Strength Training and Conditioning (formula references and training principles)
- ExRx.net — One Rep Max Calculator (1RM formula comparison)
- Wikipedia — One-Repetition Maximum (Epley and Brzycki formula definitions)
Method & review
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.