Calculator Use
Use this 1rm calculator to estimate your one-repetition maximum (1RM) for any lift, such as the bench press, squat, or deadlift. A one-rep max is the maximum amount of weight you can lift for a single repetition with proper form. Instead of risking injury by attempting a true 1RM, you can use sub-maximal weights and repetitions to predict your strength levels.
To get started, enter the weight you lifted and the number of repetitions you completed until failure. Selecting different formulas allows you to see variations in strength predictions based on different physiological models.
- Weight Lifted
- The amount of weight used for the set (lbs or kg).
- Repetitions
- The total number of reps completed with good form until technical failure.
- Formula
- The mathematical model used to calculate the max (Brzycki and Epley are the most common in the fitness industry).
How It Works
When you train for strength, knowing your 1RM is essential for programming percentages. For example, a program might call for 3 sets of 5 reps at 80% of your 1RM. This calculator uses standardized scientific formulas to provide these estimates. The two most popular formulas are:
Brzycki Formula: 1RM = Weight / (1.0278 – (0.0278 × Reps))
Epley Formula: 1RM = Weight × (1 + (Reps / 30))
- Weight: The resistance used during the set.
- Reps: The number of times the movement was repeated.
- Relationship: As reps increase, the accuracy of 1RM predictions generally decreases, especially beyond 10-12 reps.
1RM Calculation Example
Example: Let's say a lifter bench presses 225 lbs for 5 repetitions and wants to find their estimated max using the Brzycki formula.
Step-by-step solution:
- Identify Weight: 225 lbs
- Identify Reps: 5
- Multiply Reps by 0.0278: 5 × 0.0278 = 0.139
- Subtract from 1.0278: 1.0278 – 0.139 = 0.8888
- Divide Weight by result: 225 / 0.8888 = 253.15
- Estimated 1RM = 253.2 lbs
Common Questions
Why use a 1RM calculator instead of testing a max?
Testing a true one-rep max places extreme stress on the central nervous system, joints, and connective tissues. For beginners or those in the middle of a training cycle, using a 1rm calculator is safer and allows for progress tracking without requiring several days of recovery from a max-out session.
Which formula is the most accurate?
The Brzycki formula is widely considered the most accurate for reps under 10. The Epley formula is often favored for athletes and higher-rep sets. However, individual differences in muscle fiber type (fast-twitch vs slow-twitch) mean that some people are naturally better at high reps or low reps, making any formula just an "estimate."
How often should I recalculate my 1RM?
Most strength programs suggest checking your progress every 4 to 8 weeks. If you find your current weights feel too light, perform an "AMRAP" (As Many Reps As Possible) set and use the results in the 1rm calculator to update your training percentages.