One Rep Max Calculator — Free Online 1RM Estimator

How to Use the One Rep Max Calculator

1. Select your unit system: Use the toggle at the top to choose between Metric (kilograms) and Imperial (pounds). The calculator adjusts all weight displays to your chosen unit. If you train with barbells marked in pounds, select Imperial. If you train in kilograms, select Metric.
2. Enter the weight lifted: Type the weight you lifted in your most recent working set. For the best estimate, this should be a set where you lifted to near-failure with good form. Avoid using a warm-up set or a set where you stopped well short of failure, as this will produce an underestimate.
3. Enter the number of reps: Type how many complete repetitions you performed with that weight. The calculator works with any rep count from 1 to 30, but accuracy is highest between 2 and 10 reps. If you completed exactly 1 rep, your 1RM equals the weight lifted.
4. Review your results: The results panel shows your estimated 1RM from both formulas and their average. Below that, a percentage table shows recommended training weights for different rep ranges, helping you program your workouts based on your estimated max.

The calculator updates instantly whenever you change any input. Experiment with different weight and rep combinations from recent sessions to cross-check your estimate. If different sets produce significantly different 1RM estimates, the set closest to failure likely gives the most accurate result.

One Rep Max Formulas and Calculation Methods

Variables Explained

• Weight: The load lifted during the set, measured in kilograms or pounds. This is the total weight on the barbell including the bar itself, or the dumbbell/machine weight as applicable.
• Reps: The number of complete repetitions performed with proper form. A rep counts only if you completed the full range of motion for the exercise. Partial reps should not be included in the count.
• 0.0333 (Epley coefficient): An empirically derived constant that models the linear relationship between additional reps and the percentage of your 1RM. Each additional rep represents approximately 3.33% less than your true max.
• 37 (Brzycki constant): A constant derived from research on the curvilinear relationship between rep count and percentage of maximum. The formula becomes undefined at 37 reps, which represents a theoretical upper limit.

Step-by-Step Calculation Example

Suppose you bench pressed 185 lbs for 5 reps:

1. Epley formula: 185 x (1 + 0.0333 x 5) = 185 x 1.1665 = 215.8 lbs
2. Brzycki formula: 185 x (37 / (37 - 5)) = 185 x (37 / 32) = 185 x 1.15625 = 213.9 lbs
3. Average estimated 1RM: (215.8 + 213.9) / 2 = 214.9 lbs
4. Training at 80% of 1RM: 214.9 x 0.80 = 171.9 lbs (about 8 reps)
5. Training at 70% of 1RM: 214.9 x 0.70 = 150.4 lbs (about 12 reps)

The slight difference between formulas is normal. Averaging them provides a reliable working estimate for programming your training cycles. Most coaches use the average or whichever formula their specific program calls for.

Practical Examples

Example 1: Marcus Starting a 5/3/1 Program

Marcus is a 28-year-old intermediate lifter beginning the 5/3/1 strength program, which requires a training max (typically 85-90% of true 1RM). He recently squatted 225 lbs for 6 reps:

• Epley: 225 x (1 + 0.0333 x 6) = 225 x 1.1998 = 270.0 lbs
• Brzycki: 225 x (37 / 31) = 225 x 1.1935 = 268.5 lbs
• Average 1RM: 269.3 lbs
• Training max (90%): 269.3 x 0.90 = 242.4 lbs, rounded to 240 lbs

Marcus sets his squat training max at 240 lbs and programs his 5/3/1 percentages from there. After 4 weeks, he retests and adjusts.

Example 2: Jen Testing After a Hypertrophy Block

Jen is a 34-year-old recreational lifter finishing a 6-week hypertrophy phase. She wants to know her new bench press 1RM without actually attempting a max single. Her last heavy set was 95 lbs for 8 reps:

• Epley: 95 x (1 + 0.0333 x 8) = 95 x 1.2664 = 120.3 lbs
• Brzycki: 95 x (37 / 29) = 95 x 1.2759 = 121.2 lbs
• Average 1RM: 120.8 lbs

Jen's estimated bench press 1RM is approximately 121 lbs. She uses this to program her next strength block at 85% (about 103 lbs for sets of 5).

Example 3: Carlos Tracking Deadlift Progress

Carlos is a 40-year-old powerlifter who tracks his estimated 1RM every month to monitor progress without excessive maximal testing. His deadlift test set this month: 365 lbs for 3 reps:

• Epley: 365 x (1 + 0.0333 x 3) = 365 x 1.0999 = 401.5 lbs
• Brzycki: 365 x (37 / 34) = 365 x 1.0882 = 397.2 lbs
• Average 1RM: 399.4 lbs
• Last month estimate: 385 lbs (from 350 x 4)

Carlos's estimated deadlift 1RM increased by about 14 lbs over the past month, confirming his programming is working. He adjusts his training percentages upward for the next cycle.

Training Percentage Reference Table

Tips and Complete Guide to One Rep Max Estimation

Getting the Most Accurate Estimate

The quality of your 1RM estimate depends heavily on the quality of the data you feed the calculator. Test with a weight that brings you very close to failure within 3 to 8 reps. Sets that end well before failure underestimate your max, while sets with excessively high reps (15+) introduce significant error. Use the same exercise form you would use for a max attempt — tempo, range of motion, and pause length should all be consistent.

When to Use Each Formula

The Brzycki formula tends to be more conservative and is often preferred for lower rep ranges (2-6 reps), which is why it is popular in powerlifting circles. The Epley formula produces slightly higher estimates and works reasonably well across a broader rep range. For general training purposes, the average of both formulas provides the best estimate. If your training program specifies a particular formula, use that one for consistency.

Programming with Your 1RM

Most effective strength programs use percentage-based training derived from your 1RM. The concept is straightforward: if your estimated 1RM is 300 lbs and your program calls for 5 sets of 3 at 85%, you would load the bar with 255 lbs. This removes guesswork from training and ensures progressive overload. Many coaches recommend using a "training max" of 85-90% of your true estimated 1RM as the basis for percentage calculations, building in a buffer that promotes better form and long-term progress.

Exercise-Specific Considerations

1RM estimation works best for compound barbell movements like the squat, bench press, deadlift, and overhead press. For isolation exercises (curls, extensions, lateral raises), the formulas are less reliable because fatigue patterns differ and the risk of joint stress is higher. Machine exercises can also produce less accurate estimates due to variable resistance curves. Stick to free-weight compound lifts for the most useful 1RM data, and use rep targets rather than percentages for accessory work.

Common Mistakes to Avoid

• Using sets that were not taken to near-failure: If you stopped your set with 3 or more reps in reserve, the calculator will significantly underestimate your 1RM. Use a set where you could have completed at most 1 to 2 more reps.
• Testing with excessively high reps: Rep counts above 10 reduce accuracy significantly. If you only have data from a 15-rep set, the estimate may be off by 10% or more. Whenever possible, test with a heavier weight for fewer reps.
• Ignoring fatigue and conditions: Your estimated 1RM is only as good as the set it is based on. A set performed at the end of a hard workout, after poor sleep, or while underfed will produce a lower estimate than your true capacity. Test when fresh for the best data.
• Treating the estimate as exact: All formulas produce estimates, not exact measurements. Use your estimated 1RM as a guide for programming, but listen to your body. If the programmed weight feels too heavy or too light on a given day, adjust accordingly.
• Not retesting periodically: Your strength changes over time. Using an outdated 1RM leads to training weights that are either too light (no progress stimulus) or too heavy (injury risk and poor recovery). Recalculate every 4 to 8 weeks.

Frequently Asked Questions