1RM Calculator — Estimate Your One-Rep Max
Enter the weight you lifted and the number of reps to estimate your one-rep max across three proven formulas. Works for squat, bench press, deadlift, and overhead press.
How the 1RM Formulas Work
No single formula is perfect. Each makes slightly different assumptions about the relationship between submaximal weight and maximal strength. That's why this calculator shows all three — so you can triangulate rather than trust a single number blindly.
Epley Formula
1RM = weight × (1 + reps ÷ 30)
The most widely used formula in strength training. Developed by Boyd Epley at the University of Nebraska, it assumes a linear relationship between reps and intensity. Tends to overestimate slightly above 10 reps.
Brzycki Formula
1RM = weight × 36 ÷ (37 − reps)
Published by Matt Brzycki in 1993. Produces nearly identical results to Epley for sets of 1-6 reps but diverges at higher rep ranges, where it becomes more conservative. Many coaches prefer Brzycki for sets of 5 or fewer.
Lombardi Formula
1RM = weight × reps0.10
Uses an exponential model rather than a linear one. Tends to produce slightly lower estimates than Epley and Brzycki, especially at moderate rep ranges. Some lifters find Lombardi tracks their actual maxes more closely.
Why the Percentage Chart Matters
Once you know your estimated 1RM, the percentage chart tells you exactly what weight to load for any given intensity. This is how percentage-based programs like 5/3/1, Sheiko, and the Russian Squat Routine prescribe training loads.
A common mistake is using your true 1RM for programming. Most programs use a training max— typically 85-90% of your estimated 1RM. Jim Wendler's 5/3/1 sets the training max at 90%, and Greg Nuckols recommends starting even more conservatively for newer lifters. The buffer protects your progress on bad days and builds sustainable momentum.
When to Use a 1RM Calculator
- •Starting a new program.Most programs ask for your 1RM on day one. If you haven't tested it recently, a heavy set of 3-5 reps gives you a solid estimate without the injury risk of a true max attempt.
- •Recalculating after a training block. Run a 5x5 cycle or a beginner program for 8-12 weeks, then test a new heavy set to see how much your estimated max has moved.
- •Comparing lifts across weight classes. Pair your 1RM with a Wilks or DOTS calculator to see how your strength stacks up relative to bodyweight.
- •Tracking progress without maxing out. Testing a true 1RM every week is a fast track to overtraining. Estimating from submaximal sets lets you track progress safely.
Frequently Asked Questions
How accurate is a 1RM calculator?
Most formulas are accurate within 5% for sets of 1-10 reps. Above 10 reps, predictions become less reliable because muscular endurance starts influencing performance more than maximal strength. For the most accurate estimate, use a set of 3-5 reps performed to true failure.
Which 1RM formula should I use?
Epley and Brzycki produce nearly identical results for sets of 1-10 reps and are the most widely used in powerlifting. Brzycki tends to be slightly more conservative at higher rep ranges. If your 5-rep set gives you a different Epley vs Brzycki number, split the difference.
Should I test my actual 1RM or estimate it?
For programming purposes, an estimated 1RM from a heavy triple or set of five is usually sufficient and safer. True 1RM testing is best reserved for competition or peak testing days with proper warm-up protocol. Programs like 5/3/1 deliberately use a training max set below your estimated 1RM.
How often should I recalculate my 1RM?
Recalculate every 4-6 weeks or at the end of a training cycle. Beginners on linear progression may recalculate more frequently as strength gains come quickly. Avoid testing or recalculating mid-cycle — it disrupts the programming and encourages ego lifting.