What Is a One Rep Max (1RM)?

Your one-rep max (1RM) is the maximum amount of weight you can lift for a single repetition with proper form on a given exercise. It is the gold standard measure of absolute strength in resistance training and is used by coaches, athletes, and recreational lifters to design training programs, track progress, and compare strength levels.

Directly testing your 1RM requires lifting maximal loads, which carries a higher risk of injury, demands significant recovery time, and requires experience with heavy lifting. This calculator provides a safer alternative by estimating your 1RM from a submaximal effort. Simply enter the weight you lifted and the number of reps you completed, and the calculator applies multiple validated formulas to estimate the heaviest weight you could lift for one rep.

1RM Estimation Formulas

Our calculator uses four well-established formulas, each developed through research on strength training populations. Because no single formula is universally most accurate, we present results from all four so you can see the range of estimates:

Epley Formula (1985)

The Epley formula is one of the most widely used 1RM prediction equations in both research and practice:

1RM = Weight x (1 + Reps / 30)

This formula tends to be most accurate in the 2-10 rep range and is linear, meaning it predicts a consistent increase in estimated 1RM as reps decrease. It is particularly popular in powerlifting communities and is the default formula used by many training apps and percentage charts.

Brzycki Formula (1993)

Developed by Matt Brzycki, this formula uses a slightly different mathematical approach:

1RM = Weight x (36 / (37 - Reps))

The Brzycki formula produces results very similar to Epley for low rep ranges (1-6 reps) but diverges at higher rep counts. Research suggests it may slightly underestimate 1RM at higher rep ranges (10+). It is widely used in academic research and strength and conditioning programs.

Lombardi Formula (1989)

The Lombardi formula uses an exponential approach:

1RM = Weight x Reps^0.10

This formula tends to produce slightly more conservative estimates than Epley or Brzycki, particularly at higher rep counts. Some coaches prefer it because the exponential model better reflects the non-linear relationship between reps and maximum strength that is observed in practice.

O'Conner Formula (1989)

The O'Conner formula provides a simple linear estimation:

1RM = Weight x (1 + 0.025 x Reps)

This formula tends to give lower estimates than Epley and is considered more conservative overall. It is useful as a lower-bound estimate and can be a better predictor for individuals who are relatively untrained or who performed their test set at higher rep ranges.

How to Get the Most Accurate Estimate

The accuracy of any 1RM estimation depends heavily on the quality of your input data. Follow these guidelines for the best results:

Use 3-6 reps: All formulas are most accurate when the test set is between 3 and 6 repetitions. As rep count increases above 10, prediction error grows substantially, potentially reaching 10% or more.
Go to true failure (or very close): The weight and reps you enter should represent a maximum effort. If you stopped your set with 2-3 reps in reserve, the calculator will underestimate your 1RM.
Use compound exercises: These formulas were developed and validated primarily on compound lifts like the squat, bench press, and deadlift. They may be less accurate for isolation exercises or machine movements.
Be well-rested: Perform your test set when fresh, ideally at the beginning of a workout after a proper warm-up. Fatigue from prior sets will reduce your rep count and skew the estimate.

Percentage-Based Training

Once you know your 1RM (or a reliable estimate), you can use percentage-based programming to structure your training. This approach assigns specific percentages of your 1RM for different training goals:

% of 1RM	Typical Reps	Training Goal
90 – 100%	1 – 3	Maximal Strength / Peaking
80 – 90%	3 – 5	Strength
70 – 80%	6 – 8	Strength-Hypertrophy
60 – 70%	8 – 12	Hypertrophy (muscle growth)
50 – 60%	12 – 20	Muscular Endurance
30 – 50%	20 – 30+	Endurance / Warm-up

For example, if your estimated bench press 1RM is 100 kg and your program calls for 4 sets of 5 reps at 80%, you would load the bar with 80 kg. This systematic approach removes guesswork and ensures you are training at the right intensity for your goal.

Strength Standards

Strength standards provide benchmarks for evaluating your performance relative to other lifters of similar body weight and experience. While these vary across organizations, the following general guidelines for the barbell back squat give you an idea of where you stand:

Beginner (less than 6 months of training): 0.75x body weight for men, 0.5x body weight for women.
Novice (6-12 months): 1.25x body weight for men, 0.75x body weight for women.
Intermediate (1-3 years): 1.5-1.75x body weight for men, 1.0-1.25x body weight for women.
Advanced (3-5+ years): 2.0-2.5x body weight for men, 1.5-1.75x body weight for women.
Elite (competitive level): 2.5x+ body weight for men, 2.0x+ body weight for women.

These benchmarks are approximate and vary by exercise. Bench press standards are typically lower, while deadlift standards are typically higher than squat standards. Use them as general guideposts rather than strict targets.

Progressing Your 1RM Over Time

Strength improvements follow a predictable pattern. Beginners can add weight to the bar almost every session (linear progression), often increasing their 1RM by 2.5-5 kg per week on major lifts. Intermediate lifters progress more slowly, typically adding 1-2 kg per month through periodized programming. Advanced lifters may take months to add even a few kilograms, requiring sophisticated programming strategies like block periodization, wave loading, or conjugate methods.

Regardless of experience level, the key drivers of 1RM improvement remain the same: consistent training with progressive overload, adequate nutrition (particularly protein at 1.6-2.2g per kg of body weight), sufficient sleep (7-9 hours per night), and structured deload periods every 4-8 weeks to manage fatigue accumulation.

Next step: Use your 1RM to program percentage-based training. To support your strength goals, calculate your daily nutrition needs with the TDEE Calculator and optimize your protein intake with the Macro Calculator.

Frequently Asked Questions

When using a test set of 3-6 reps performed to near failure, 1RM estimates are typically within 5% of your actual max. Accuracy decreases with higher rep counts: at 10+ reps, error can reach 10% or more. For the most reliable estimate, use the average of all four formulas and test with a weight you can lift for 3-5 reps at true maximum effort.

No single formula is universally most accurate. The Epley and Brzycki formulas tend to be the most validated in research and are very similar at low rep ranges. Lombardi and O'Conner tend to be slightly more conservative. The best approach is to compare all four results and use the average or the formula that most closely matches your actual tested 1RM from past experience.

For most lifters, using a calculator with a 3-5 rep test set is safer and more practical. Actual 1RM testing should be reserved for experienced lifters who need precise maxes for competition or peaking programs, and should always be done with a spotter and proper warm-up protocol. Beginners and intermediate lifters can rely on calculated estimates for effective program design.

The sweet spot is 3-6 repetitions. This range provides the most accurate predictions across all formulas. Sets of 1-2 reps are nearly as accurate but offer less data for the formula to work with. Sets above 10 reps introduce significant error because muscular endurance, technique fatigue, and cardiovascular factors begin to limit performance more than raw strength.

Recalculate every 4-8 weeks, typically at the end of a training block or mesocycle. This ensures your working weights stay appropriate as you get stronger. Avoid recalculating too frequently (weekly), as short-term fluctuations in performance due to sleep, stress, or nutrition can give misleading results. Track the trend over time rather than reacting to any single test.

These formulas were developed and validated primarily on compound barbell exercises (squat, bench press, deadlift, overhead press). They work reasonably well for dumbbell compound movements. They are less reliable for isolation exercises, machine exercises, or bodyweight movements where biomechanics and fatigue patterns differ significantly from barbell lifts.

Percentage-based training assigns weights as a percentage of your 1RM for each exercise. For example, 80% of your 1RM for sets of 5. This approach ensures you train at the right intensity for your goal (strength, hypertrophy, or endurance), provides a structured progression framework, and removes the guesswork from loading decisions. It is the foundation of most professional strength and conditioning programs.

Each formula uses a different mathematical model of the relationship between weight, reps, and maximum strength. Epley uses a linear model, Brzycki uses a ratio model, Lombardi uses an exponential model, and O'Conner uses a conservative linear model. At low reps (3-5), the formulas converge closely. At higher reps, they diverge because the underlying assumptions about fatigue and rep-strength curves differ.

One Rep Max Calculator