CalcOne Rep Max (Brzycki) Calculator
One Rep Max (Brzycki) Calculator. Free online calculator with formula, examples and step-by-step guide.
One Rep Max Brzycki Calculator: Estimate Max Strength Safely
The Brzycki one rep max calculator estimates your one-repetition maximum (1RM) from a submaximal set of multiple reps, eliminating the need to attempt a potentially dangerous maximal lift. The Brzycki formula, developed by Matt Brzycki at Princeton University, is one of the most widely validated prediction equations in strength and conditioning. It is particularly popular in collegiate and high school athletic programs because it allows coaches to estimate athletes' max strength without exposing them to the injury risk of a true 1RM attempt. Whether you are a powerlifter planning your next training cycle, a general fitness enthusiast wanting to track progress, or a coach programming safe training loads, this calculator provides reliable strength estimates from weights you can handle comfortably.
Brzycki 1RM Formula
1RM = Weight × (36 / (37 − Reps))
Where Weight is the load lifted in kilograms or pounds (output same unit), and Reps is the number of complete repetitions performed with perfect form. The formula is valid for up to 10 repetitions, with optimal accuracy between 3 and 8 reps. For example, if you bench press 80 kg for 5 reps: 1RM = 80 × 36 / (37 − 5) = 80 × 36/32 = 80 × 1.125 = 90 kg. This means your estimated maximum single-rep bench press is 90 kg.
The Brzycki formula is based on the observed linear relationship between the number of reps performed and the percentage of 1RM that can be sustained. At 1 rep, you lift 100% of 1RM. At 10 reps, you are lifting approximately 75% of 1RM. The formula models this drop-off mathematically. Compared to other popular formulas like Epley (1RM = w × (1 + r/30)), Brzycki tends to give slightly more conservative estimates at higher rep ranges, which many coaches prefer for safety. The American College of Sports Medicine references the Brzycki formula as a valid method for 1RM estimation in their guidelines for resistance training.
Worked Examples
Example 1: Bench Press at 8 Reps
A lifter completes 8 reps of bench press with 70 kg (154 lbs) with good form.
Calculation: 1RM = 70 × 36 / (37 − 8) = 70 × 36 / 29 = 70 × 1.241 = 86.9 kg
His estimated 1RM is approximately 87 kg. The 70 kg for 8 reps represents about 80.5% of his 1RM. Using this estimate, his training zones can be programmed: hypertrophy work (65–75% of 1RM) would be 57–65 kg for 8–12 reps, strength work (80–90% of 1RM) would be 70–78 kg for 3–6 reps, and peaking work (90%+) would be above 78 kg for 1–3 reps. He should retest when 70 kg becomes comfortable for 10–12 reps, at which point his estimated 1RM would increase to approximately 93 kg.
Example 2: Deadlift at 3 Reps
A more advanced lifter pulls 140 kg for 3 reps on the deadlift.
Calculation: 1RM = 140 × 36 / (37 − 3) = 140 × 36 / 34 = 140 × 1.059 = 148.2 kg
His estimated 1RM is 148 kg. The 3-rep set provides a more confident estimate (within ±2–3%) than a higher-rep set would. At approximately 94.5% of 1RM, this is a heavy set that requires good technique to complete safely. For programming, his 5×5 working sets would be around 125 kg (85% of 1RM), and his warm-up scheme might be: 60 kg × 8, 100 kg × 5, 130 kg × 3, then work sets. Many experienced deadlifters find the Brzycki formula slightly underestimates their true 1RM for deadlifts by about 3–5%, so his actual maximum might be closer to 152–155 kg. If he adds 10 kg to his 3-rep max over a training block, his estimated 1RM would rise to approximately 159 kg.
Common Uses
- Programming percentage-based training loads for strength phases without requiring athletes to perform risky maximal lifts
- Tracking long-term strength progression across training cycles using consistent estimation methodology from submaximal sets
- Designing deload weeks by calculating the appropriate percentage reduction from estimated 1RM every 4–6 weeks
- Comparing estimated strength levels across different exercises (bench press, squat, deadlift, overhead press) to identify weak points
- Setting competition openers for powerlifting meets based on conservative 1RM estimates to ensure a successful first attempt
- Adjusting training loads after a layoff or injury recovery where estimated 1RM gives a safe starting point below previous max levels
Common Mistakes
- Using reps performed with poor form or compromised range of motion — partial reps and cheated reps overestimate strength because they do not represent true muscular capacity
- Applying the formula to sets with more than 10 reps — beyond 10 reps, muscular endurance and metabolic fatigue dominate, and the linear relationship assumed by Brzycki breaks down
- Testing 1RM too frequently and programming near-maximal loads every session, which leads to accumulated central nervous system fatigue and increased injury risk
- Forgetting to account for fatigue from previous exercises — the Brzycki estimate is most accurate when test sets are performed on fresh muscles early in the workout
- Using the formula with different rep-max combinations from different days and averaging them, when the most reliable estimate comes from a single well-executed set
Pro Tip
For the most accurate Brzycki estimates, use a rep range of 3–5 on compound lifts and 6–8 on isolation exercises. Perform a thorough warm-up: 2 sets of 5–8 reps with 40–50% of estimated 1RM, then 1 set of 3 reps at 70–75%, rest 2–3 minutes, then attempt your test set. Choose a weight you can complete for exactly 3–5 reps with one rep left in the tank (RIR 1). If you complete the set and could have done 2 or more additional reps, the weight was too light for an accurate estimate. Re-test on the same day after 5 minutes rest with a 2.5–5 kg increase. Track your estimated 1RM for each major lift in a training log, and consider it validated when you can perform a formerly maximal weight for 2–3 reps.
Frequently Asked Questions
Brzycki (1RM = w × 36/(37-r)) and Epley (1RM = w × (1 + r/30)) give similar results for 1–5 reps but diverge at 8–10 reps, with Brzycki being more conservative. Brzycki predicts within ±5% for most lifters using 10 or fewer reps. Above 10 reps, both formulas lose accuracy.
Fewer reps give better accuracy. Testing with 3–5 reps is ideal: heavy enough to predict but safe. At 3 reps, error margin is ~±2–3%. At 10 reps, error increases to ±5–8% because muscular endurance affects performance significantly.
Yes, but with caution. The formula was developed from bench press. For squat and deadlift, accuracy is slightly lower. Some studies suggest adding 5–10% to the Brzycki estimate for deadlift in experienced lifters due to different neuromuscular demands.
Every 4–8 weeks for most programs. Beginners recalculate every 2–4 weeks. Advanced lifters need 8–12 weeks. When a set feels noticeably easier than the previous week at the same weight, it is time to recalculate and adjust loads upward.