One-Rep Max Calculator
Estimate your one-rep max (1RM) for any lift using the Epley and Brzycki formulas, then see a full training percentage table showing the weight for each intensity level.
How It Works
A one-rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. Directly testing 1RM carries injury risk, so estimation formulas allow you to calculate it from a sub-maximal set.
Epley Formula (1985):
1RM = weight × (1 + reps / 30)
Brzycki Formula (1993):
1RM = weight × 36 / (37 − reps)
Both formulas are most accurate for sets of 1–10 repetitions. Accuracy decreases as rep count rises — at 20+ reps, muscular endurance becomes a bigger factor than maximal strength, and the formulas tend to overestimate 1RM.
The Epley formula is slightly more forgiving at higher rep ranges. The Brzycki formula can produce a divide-by-zero error at 37 reps (37 − 37 = 0), so it is typically only used up to 30 reps in practice.
Training percentage table: Once you know your 1RM, you can prescribe training intensity scientifically:
- 50–60%: Light, warm-up / technique work
- 65–75%: Hypertrophy / higher-rep training
- 80–85%: Strength building (3–5 reps)
- 90–95%: Near-maximal strength (1–3 reps)
- 100%: True 1RM (test only, not regular training)
Most strength training programs prescribe intensity as a percentage of 1RM (e.g., "5×5 at 75% 1RM"). Knowing your estimated 1RM lets you load each session correctly.
Frequently Asked Questions
Which formula is more accurate?
For sets of 2–10 reps, both formulas perform similarly, with errors typically within 2–5%. The Epley formula tends to slightly overestimate at very low rep counts (2–3 reps). The Brzycki formula is generally considered marginally more accurate for sets of 2–6 reps. Using the average of both gives a reasonable middle estimate.
How many reps should I use for the estimate?
Sets of 3–8 reps give the most accurate estimates. The closer the set is to true failure (last rep is genuinely your limit), the more reliable the prediction. Avoid estimating from sets of 15+ reps — the formulas become unreliable because endurance capacity clouds the pure strength measurement.
Is testing my actual 1RM safer?
For experienced lifters with good technique, a 1RM test performed with a spotter and proper warm-up is reasonably safe. For beginners or those returning from injury, formula-based estimation from a submaximal set is safer and adequate for programming purposes.
How often should I re-test my 1RM?
Re-estimate every 4–8 weeks, or at the end of a training cycle, to update your training percentages as your strength progresses. Regular 1RM testing (more than every 2–3 weeks) is generally not productive and adds unnecessary fatigue.