116.7
kg
99.2
kg
87.5
kg
75.8
kg
58.3
kg
116.7
kg
99.2
kg
87.5
kg
75.8
kg
58.3
kg
The One Rep Max (1RM) Calculator estimates the maximum weight you can lift for a single repetition based on the weight and number of repetitions performed in a submaximal set. Knowing your one rep max is fundamental to strength training programming because training loads are typically prescribed as percentages of 1RM. Whether you follow a powerlifting program like Wendler's 5/3/1, a bodybuilding hypertrophy protocol, or a general strength program, your 1RM determines the weights you should use for every set in your training plan.
Directly testing your true 1RM requires lifting a maximal load, which carries significant injury risk, requires extensive warm-up, demands a spotter, and is physically taxing enough to require several days of recovery. For these reasons, exercise scientists have developed regression equations that predict 1RM from submaximal performance. This calculator implements four of the most widely validated formulas, each with slightly different mathematical approaches and accuracy profiles.
The Epley formula, published by Boyd Epley of the University of Nebraska, uses a linear relationship: $$1RM = w \times \left(1 + \frac{r}{30}\right)$$ where \(w\) is the weight lifted and \(r\) is the number of repetitions. This formula is simple, widely used, and reasonably accurate for repetition ranges of 1-10. It tends to overestimate 1RM at higher rep ranges (above 12) because the linear assumption breaks down as fatigue patterns become more complex.
The Brzycki formula, developed by Matt Brzycki of Princeton University, uses: $$1RM = w \times \frac{36}{37 - r}$$ This formula produces very similar results to Epley for low rep ranges but diverges at higher rep counts. It approaches infinity as reps approach 37, which is a mathematical limitation rather than a physiological reality. For practical purposes, both Epley and Brzycki are considered equally accurate for sets of 1-10 repetitions.
The Lombardi formula uses an exponential model: $$1RM = w \times r^{0.10}$$ This approach assumes a power-law relationship between repetitions and load, which some researchers argue better reflects the nonlinear nature of neuromuscular fatigue. The Lombardi formula tends to produce slightly lower estimates than Epley and Brzycki, making it arguably more conservative and potentially safer for training load prescription.
The O'Conner formula provides another linear estimate: $$1RM = w \times (1 + 0.025 \times r)$$ With a coefficient of 0.025 per repetition compared to Epley's 0.0333 (1/30), the O'Conner formula produces slightly more conservative estimates. It was developed from research on collegiate athletes and tends to perform well across a range of exercises and training populations.
The calculator also provides percentage-based training loads derived from your estimated 1RM. Training at 85% of 1RM typically corresponds to approximately 5 repetitions and is used for strength development. 75% of 1RM corresponds to about 10 repetitions and targets the hypertrophy rep range for muscle growth. 65% of 1RM allows approximately 15 repetitions and develops muscular endurance. 50% of 1RM is a standard warm-up load. These percentages are based on the Repetition Maximum Continuum, a well-established framework in exercise science.
For maximum accuracy, use a weight that allows 3-7 repetitions with good form. Predictions become less reliable beyond 10 repetitions because fatigue patterns vary significantly between individuals and exercises. Compound lifts (squat, deadlift, bench press) tend to follow prediction equations more closely than isolation exercises. Always round predicted loads to the nearest available weight plate increment in your gym.
The calculator applies the selected formula to estimate your one-repetition maximum:
Epley: $$1RM = w \times \left(1 + \frac{r}{30}\right)$$
Brzycki: $$1RM = w \times \frac{36}{37 - r}$$
Lombardi: $$1RM = w \times r^{0.10}$$
O'Conner: $$1RM = w \times (1 + 0.025 \times r)$$
where \(w\) is the weight lifted and \(r\) is the number of repetitions completed. If only 1 rep is entered, the weight itself is your 1RM. Percentage outputs are calculated as simple fractions of the estimated 1RM.
The Estimated 1RM is the maximum weight you could theoretically lift for one repetition. Use this as a baseline for programming. 85% of 1RM is your target for heavy strength sets (3-5 reps). 75% of 1RM is ideal for hypertrophy training (8-12 reps). 65% of 1RM suits muscular endurance work (12-20 reps). 50% of 1RM is appropriate for warm-up sets. If different formulas give substantially different estimates, use the average or the more conservative value for safety.
Inputs
Results
Epley: 100 x (1 + 5/30) = 116.7 kg estimated 1RM. Program strength work at ~99 kg (85%), hypertrophy at ~88 kg (75%).
Inputs
Results
Brzycki: 140 x 36 / (37 - 3) = 148.2 kg estimated 1RM. At 3 reps, Epley and Brzycki give very similar results.
For rep ranges of 1-6, Epley and Brzycki produce nearly identical results and are both well-validated. For higher rep ranges (7-12), Brzycki may be slightly more accurate. The Lombardi formula tends to be more conservative. Using the average of multiple formulas provides the most robust estimate.
Use a weight that allows 3-7 repetitions with proper form. Predictions are most accurate in this range. Above 10 reps, accuracy decreases significantly because individual fatigue patterns vary widely and psychological factors play a larger role.
No. Prediction accuracy varies by exercise. Compound movements like squat, bench press, and deadlift tend to follow prediction equations well. Isolation exercises, machine exercises, and exercises with high skill components may deviate more from predicted values.
Recalculate every 4-8 weeks as your strength changes, or whenever you start a new training program. If your training weights feel consistently too easy or too hard, an updated 1RM estimate will recalibrate your working weights.
Yes, but beginners should use higher rep ranges (8-10 reps) for the test set rather than attempting heavy singles or triples. Beginners also improve rapidly, so recalculate frequently. Focus on learning proper form before worrying about maximal strength numbers.
The Brzycki formula has 37 - reps in the denominator, so it approaches infinity as reps approach 37. This is a mathematical artifact, not a physiological reality. For rep ranges above 12-15, none of the prediction formulas are reliable, and direct testing or alternative assessments should be used.
Roboculator Team
The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
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