One Rep Max (1RM) Calculator
Enter the weight you lifted and how many reps you completed. Get your estimated one rep max instantly using 7 proven strength formulas. Free, no signup required.
How It Works
How to Calculate Your 1RM
Your one rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. It is the gold standard for measuring absolute strength and is used by coaches, athletes, and lifters worldwide to program training percentages and track long-term progress.
Rather than loading a barbell to your absolute limit and risking injury, you can estimate your 1RM from a submaximal set. Lift a weight for 3 to 10 reps, enter the numbers into the calculator above, and get a reliable estimate. This is safer, faster, and just as useful for programming your workouts.
Every formula in this calculator takes two inputs: the weight you lifted and the number of reps you completed. They each use a slightly different mathematical model to extrapolate what you could lift for one rep. The closer your set is to 1 rep, the more accurate the estimate.
Formulas
Which Formula Should I Use?
Seven peer-reviewed formulas, each with different strengths. For most lifters, Epley is the best default. IronStreak uses Epley for all Progress tracking in the app.
Epley
RecommendedThe most widely used formula. Best for moderate rep ranges (3-10 reps). Slightly overestimates at very high reps. Used by IronStreak, most gym apps, and the NSCA.
Brzycki
More conservative than Epley at higher rep ranges. Popular in powerlifting communities. Gives similar results to Epley at low reps (1-6) and diverges above 10 reps.
Lombardi
Uses a power function rather than a linear model. Tends to produce slightly higher estimates. Useful for cross-referencing other formulas.
Mayhew
Uses an exponential regression model. Validated primarily with bench press data. Good secondary option for upper body lifts.
O'Conner
A simple linear formula. Easy to calculate by hand. Less accurate at high reps but serviceable for quick mental math in the gym.
Wathan
Uses an exponential model similar to Mayhew but with different coefficients. Some studies suggest it is more accurate for trained athletes.
Lander
A linear regression formula. Breaks down above 12 reps but is accurate in the 1-10 range. A good sanity check alongside Epley or Brzycki.
Popular Exercises to Calculate
Frequently Asked Questions
What is a one rep max?
A one rep max (1RM) is the maximum amount of weight you can lift for a single repetition with proper form. It is the gold standard for measuring absolute strength on any given exercise and is used to program training percentages, track long-term progress, and compare strength across different body weights.
How accurate are 1RM calculators?
1RM calculators are most accurate when using sets of 1 to 10 reps. Beyond 10 reps, the estimates become less reliable because muscular endurance starts to play a bigger role than raw strength. For best results, use a weight you can lift for 3 to 6 reps with good form. The Epley and Brzycki formulas are the most widely validated in research.
Should I test my actual 1RM?
For most people, estimating your 1RM from a submaximal set (3 to 5 reps) is safer and just as useful for programming. True 1RM testing carries a higher injury risk and requires proper warm-up, a spotter, and experience with near-maximal loads. Competitive powerlifters and weightlifters test true 1RMs in meets, but recreational lifters rarely need to.
How does IronStreak track my 1RM?
IronStreak automatically calculates your estimated 1RM from every set you log using the Epley formula. It tracks your best estimated 1RM over time and charts it on the Progress tab with time range filters (1 month, 3 months, 1 year, all time). Your PR Board shows your all-time best for every exercise. Learn more about Progress tracking.
Track Your 1RM Progress Over Time
IronStreak automatically calculates your estimated 1RM from every workout and charts it over time. Watch your strength grow with real data, not guesswork. Browse our exercise library of 91 exercises, track progress with charts and PRs, and stay consistent with streaks and XP.
Free to download. See pricing for Pro features.