How to Estimate Your One-Rep Max (1RM): Formulas, Science, and Practical Use

What a One-Rep Max Is — and Why It Matters

A one-repetition maximum, or 1RM, is the maximum weight a person can lift for a single complete repetition of a given exercise with proper technique. It is the gold standard measure of maximal strength in resistance training.

The 1RM concept matters primarily as a programming tool. Strength and hypertrophy training programs commonly prescribe loads as percentages of 1RM — for example, “5 sets of 3 at 85% 1RM” or “3 sets of 8–12 at 65–75% 1RM.” These percentages correspond to different physiological training stimuli: near-maximal loads (90–100% 1RM) develop maximal strength and neural efficiency; moderate loads (60–80% 1RM) build muscle hypertrophy; lighter loads (40–60% 1RM) develop muscular endurance. Without a reasonably accurate 1RM estimate, those percentage-based prescriptions are imprecise.

The 1RM is also a standardized measure for tracking strength progress over time and for comparing performance across athletes of different sizes and training histories.

Direct Testing vs. Predictive Formulas

The true 1RM can be measured directly: load the bar progressively until a single repetition cannot be completed, record the heaviest successful lift. Direct 1RM testing is standard in powerlifting competition (squat, bench press, deadlift are all contested as single-rep maxima), in laboratory exercise physiology, and in some high-performance strength programs.

Direct testing has limitations that make it impractical for many lifters:

• It requires a high level of warm-up and preparation to perform safely.
• The risk of injury is meaningfully higher than submaximal training.
• It causes significant fatigue and requires full recovery before normal training resumes.
• It is technically demanding — a lifter who has not practiced maximal singles may fail to perform optimally on the day of the test.

Predictive formulas estimate the 1RM from a submaximal set: the lifter performs a set at a weight they can handle for a known number of repetitions (for example, 100 kg for 5 repetitions), and the formula uses those two inputs to predict the load that would produce a single-rep maximum. The estimated 1RM is less accurate than a directly measured value, but it is safer to obtain, easier to repeat, and sufficient for most practical programming purposes.

The Six Standard Prediction Formulas

The calculator implements six formulas drawn from peer-reviewed exercise science literature. Each uses two inputs: the weight lifted (W, in kg) and the number of repetitions completed (R). All six were developed and validated specifically for predicting 1RM from submaximal sets.

Brzycki (1993)

1RM = W × 36 / (37 − R)

Source: Brzycki M. “Strength Testing — Predicting a One-Rep Max from Reps to Fatigue.” Journal of Physical Education, Recreation and Dance 1993; 64(1):88–90.

The Brzycki formula is the most widely cited predictive formula in popular strength training literature and is commonly used in fitness applications. It assumes a linear relationship between load and the maximum number of repetitions it permits. The formula is undefined at R = 37 (the denominator would be zero); the calculator caps R at 36 for this reason. Accuracy is highest in the 1–10 repetition range; estimates at higher rep counts become progressively less reliable.

Epley (1985)

1RM = W × (1 + R / 30)

Source: Epley B. “Poundage Chart.” Boyd Epley Workout. 1985.

Boyd Epley, strength coach at the University of Nebraska, published this formula as a coaching tool for quick load estimation. It produces a simple linear estimate and tends to predict slightly higher values than Brzycki at moderate rep counts. The Epley formula is integrated into many early strength training computer programs and continues to appear in fitness industry materials.

Lombardi (1989)

1RM = W × R^0.10

Source: Lombardi VP. Beginning Weight Training. W.C. Brown, 1989.

The Lombardi formula uses a power function, producing a modest upward adjustment as rep count increases. It is less sensitive to rep count than the other formulas and can underestimate at very low rep counts.

Mayhew et al. (1992)

1RM = 100 × W / (52.2 + 41.9 × e^(−0.055 × R))

Source: Mayhew JL, Ball TE, Arnold MD, Bowen JC. “Muscular endurance repetitions to predict bench press strength in men of different training levels.” Journal of Sports Medicine and Physical Fitness 1992; 32(1):47–51.

The Mayhew formula uses an exponential function, reflecting the non-linear relationship between load and repetitions at higher rep counts. It was developed specifically from bench press data in men across different training experience levels. The exponential decay term allows it to remain reasonably accurate across a wider rep range than the simpler linear formulas.

O’Conner et al. (1989)

1RM = W × (1 + R / 40)

Source: O’Conner B, Simmons J, O’Shea P. “Myths About Weight Training.” World Weightlifting 1989.

The O’Conner formula is structurally similar to Epley but uses a divisor of 40 rather than 30, producing lower 1RM estimates at the same rep count. It tends toward more conservative predictions and may better model intermediate-to-advanced lifters whose strength-endurance relationship differs from novices.

Wathan (1994)

1RM = 100 × W / (48.8 + 53.8 × e^(−0.075 × R))

Source: Wathan D. “Load Assignment.” In Baechle TR (ed.), Essentials of Strength Training and Conditioning. Human Kinetics, 1994; pp. 435–446.

The Wathan formula is another exponential model, similar in structure to Mayhew but with different constants derived from a broader dataset. It appears in the NSCA’s Essentials of Strength Training and Conditioning — the primary textbook for the Certified Strength and Conditioning Specialist (CSCS) credential — and is widely used in professional strength coaching contexts.

Worked Example

A lifter completes 5 repetitions with 100 kg on the barbell squat.

Inputs:

• Weight: 100 kg
• Repetitions: 5

Formula results:

Average (consensus estimate): 115.8 kg

Primary estimate (Brzycki): 112.5 kg

The spread across formulas — from 112.5 kg to 119.0 kg — illustrates the inherent uncertainty in any prediction. For programming purposes, a conservative approach uses the lower end of the range; a moderate approach uses the average.

Accuracy and Limitations

No predictive formula matches an actual tested 1RM exactly. Several factors affect accuracy:

Repetition range matters significantly. All six formulas are most accurate when the submaximal set falls in the 1–10 repetition range. As rep count increases beyond 10, prediction error grows substantially. A set of 20 repetitions at a given weight will typically yield a much less accurate 1RM estimate than a set of 5 repetitions, because the relationship between endurance capacity and maximal strength is more variable across individuals at higher rep counts.

Individual differences in strength-endurance ratio. Some individuals have a high maximal strength relative to their rep-max performance; others show the opposite. These individual differences mean the “right” formula varies by person and cannot be known without directly testing the 1RM.

Exercise specificity. The formulas were developed largely from bench press, squat, and leg press data. They may perform differently for exercises with different biomechanical profiles or that rely more heavily on technique.

Training status. Novice lifters often find predictive estimates less accurate than experienced lifters, in part because technical efficiency on near-maximal loads differs from technical efficiency at moderate loads.

Fatigue state. The submaximal set must be performed fresh (or in a comparable state to the intended 1RM test) for the estimate to be meaningful. A set performed after significant prior training volume does not produce a reliable estimate.

For most training programming purposes, the estimate is sufficiently accurate. For powerlifting competition or other contexts where the true maximum matters, direct testing or attempts-based coaching are more appropriate.

How to Conduct a Safe Submaximal Test

To get the most accurate estimate from a predictive formula:

1. Choose an appropriate weight. Select a weight you expect to complete for 3–8 repetitions. Sets in this range produce the most reliable estimates. Higher rep sets (10+) produce estimates with greater uncertainty.

2. Warm up progressively. Perform several sets at progressively heavier loads — for example, 40%, 60%, and 80% of your estimated training max — before the test set. Each warm-up set should feel increasingly demanding without creating meaningful fatigue.

3. Rest adequately. Take at least 3–5 minutes of rest before the test set. Insufficient rest allows fatigue from warm-up to suppress performance and underestimate the 1RM.

4. Lift to technical failure, not beyond. Stop the set at the last repetition where full technique is maintained. Grinding out poorly formed reps after technical failure adds injury risk without meaningfully improving the estimate.

5. Record both the weight and the exact number of completed repetitions. An estimate based on “about 8 reps” is less precise than one based on a confirmed count of 8 with good technique throughout.

Using the 1RM Estimate for Programming

Once a 1RM estimate is available, percentage-based training prescriptions become actionable:

For example, if the estimated 1RM for the bench press is 115 kg, a hypertrophy-focused session might prescribe 75% × 115 kg ≈ 86 kg for sets of 8–12 repetitions.

Percentage-based programming works best when the 1RM estimate is reasonably current and the lifter’s training is progressing on a normal trajectory. As strength improves, the 1RM should be re-estimated periodically (every 4–12 weeks depending on program phase) to keep the percentage-based loads accurate.

Frequently Asked Questions

Should I directly test my 1RM or use a formula? For most recreational lifters, predictive formulas are preferable to direct 1RM testing because they are safer, easier to repeat, and produce estimates accurate enough for programming purposes. Direct testing is most appropriate when the exact 1RM matters — powerlifting competition, detailed research, or peaking phases in advanced programs. Beginners should avoid direct 1RM testing; the risk-to-benefit ratio is unfavorable when technique under near-maximal load is not yet well-established.

Which formula should I use? The Brzycki formula is the most widely used in practice and is often cited as the default. The consensus average across all six formulas provides a slightly more robust estimate by reducing the influence of any single formula’s individual biases. In the worked example above, Brzycki estimated 112.5 kg while the average was 115.8 kg — using the average is a reasonable hedge when you are unsure which formula fits your strength-endurance profile best.

How often should I re-test? Novices (first 6–12 months of training) improve quickly enough that re-testing every 4–6 weeks may be warranted. Intermediate and advanced lifters progress more slowly; re-testing every 8–12 weeks is generally sufficient. Many programs build in scheduled “testing weeks” at the end of training blocks for this purpose.

Do women use the same formulas? Yes. The formulas predict 1RM from the relationship between submaximal weight and rep count. While average strength levels differ between men and women, the relative shape of the strength-endurance curve is similar enough that the same formulas apply. The inputs (weight and reps) reflect actual performance, so the formula output is adjusted by the inputs rather than by sex.

Can I use these formulas for any exercise? The formulas were developed and validated primarily for multi-joint compound exercises — bench press, squat, deadlift, and similar. They can be applied to other exercises, but predictive accuracy may differ. Exercises with a large skill component (Olympic lifts, gymnastics movements) are particularly poorly suited to predictive 1RM estimation because technique under maximal load is a major variable.

What is RPE and how does it relate to 1RM? Rate of Perceived Exertion (RPE) on the Borg CR10 scale, or its strength-training adaptation (the Reps in Reserve / RIR scale), is a complementary tool for regulating training intensity. An RPE-based approach adjusts load based on how hard a set felt, which automatically accounts for day-to-day variation in readiness (sleep, stress, recovery). Percentage-based programming based on estimated 1RM and RPE-based programming can be combined — for example, prescribing a load near 80% of estimated 1RM and adjusting within a session based on RPE feedback.