🏋️ One Rep Max Calculator

Estimate your one-repetition maximum (1RM) — the most weight you can lift for a single rep — using four validated strength formulas: Epley, Brzycki, Lombardi, and Mayhew. Enter the weight you lifted and how many reps you completed to get your estimated 1RM and a full training percentage table.

Weight lifted (kg)

Reps performed (1–30)

Estimated 1RM (Average)

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Epley

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Brzycki

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Lombardi

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Mayhew

Training Percentage Table

% of 1RM	Weight	Est. Reps

What is One Rep Max (1RM)?

One Rep Max (1RM) is the maximum amount of weight an athlete can lift for a single repetition of a given exercise with proper form. It is the gold-standard measure of absolute strength in resistance training, used by powerlifters, Olympic weightlifters, strength and conditioning coaches, and gym athletes to quantify maximal force production. The 1RM establishes a baseline from which training loads are prescribed — typically as a percentage of 1RM (e.g., 70% 1RM for hypertrophy sets, 85–95% 1RM for strength sets).

Directly testing 1RM requires maximal effort, thorough warm-up, and ideally a spotter for safety — particularly on compound lifts like the squat, bench press, and deadlift. As an alternative, submaximal prediction formulas estimate the 1RM from the weight lifted for a known number of repetitions (typically 2–10 reps). These formulas — developed by researchers including Brzycki, Epley, Lander, O'Conner, and others — allow strength assessment without the injury risk associated with true maximal attempts.

Once the 1RM is established, training zones can be programmed with precision: 90–100% 1RM targets maximal strength, 80–90% develops strength-hypertrophy, 70–80% targets hypertrophy, and 50–70% is used for muscular endurance. Periodic 1RM re-testing (every 4–8 weeks) tracks strength progression and allows recalibration of training loads as the athlete improves, making it an indispensable tool for periodised strength programmes.

1RM Formulas

Epley: 1RM = weight × (1 + reps / 30)

Brzycki: 1RM = weight × 36 / (37 − reps)

Lombardi: 1RM = weight × reps^0.10

Mayhew: 1RM = 100 × weight / (52.2 + 41.9 × e^{−0.055 × reps})

The Epley formula is the most widely used and generally performs well across all rep ranges. The Brzycki formula is particularly accurate for lower rep ranges (1–10) but becomes invalid above 36 reps. The average of all four formulas provides the most robust estimate.

How to Use the One Rep Max Calculator

1

Select Your Unit System

Choose metric (kg) or imperial (lbs) depending on the unit your equipment uses. The results will display in the same unit.
2

Enter the Weight Lifted

Enter the load you used for your set. Use the actual weight on the bar including any plates.
3

Enter Reps Performed

Enter how many reps you completed with that weight. For best accuracy, aim for 3–10 reps — estimates become less reliable above 10 reps.
4

Read Your 1RM and Table

See your estimated 1RM from four formulas plus the average. Use the training percentage table to plan your working weights for different goals.

Example Calculation

A lifter completes 5 reps with 100 kg:

Epley: 100 × (1 + 5/30) = 116.7 kg

Brzycki: 100 × 36/(37−5) = 112.5 kg

Lombardi: 100 × 5^0.10 = 117.5 kg

Mayhew: 100×100/(52.2+41.9×e^(−0.275)) ≈ 117.9 kg

Average 1RM = 116.2 kg

Frequently Asked Questions

What is One Rep Max (1RM)?

One Rep Max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with proper form. It is the gold standard measure of strength and is used to prescribe training loads as a percentage of 1RM. Testing your true 1RM directly is possible but carries injury risk, so the formulas in this calculator provide a safe estimate from a sub-maximal set.

Which formula is most accurate?

No single formula is universally best — accuracy depends on the individual and the rep range used. The Epley formula is the most widely cited and performs consistently across rep ranges. Brzycki is highly accurate for 1–10 reps. For the most reliable estimate, this calculator averages all four formulas. Always treat the result as an estimate and approach true maximal attempts with caution.

How often should I test my 1RM?

For most lifters, testing or estimating 1RM every 4–8 weeks is sufficient to track progress. Beginners often improve quickly enough to re-test monthly. Advanced lifters may test less frequently. Rather than performing true 1RM attempts regularly, many coaches recommend estimating 1RM from a 3–5 rep set every training cycle for safety and recovery reasons.

What if I perform more than 10 reps?

The accuracy of all 1RM estimation formulas decreases significantly beyond 10 reps. At higher rep counts, the relationship between reps and maximum strength becomes less predictable because muscular endurance plays a larger role. For the most accurate estimate, choose a weight that limits you to 3–6 reps. Results from sets of 15+ reps should be treated as rough approximations only.

Real-World Applications

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Powerlifting Competition Preparation

Determine peak-week training loads as a percentage of predicted competition 1RM — allowing precise tapering so the athlete peaks on competition day without overtraining in the final weeks.

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Hypertrophy Programme Design

Programme 3–4 sets of 8–12 reps at 70–80% 1RM for maximum muscle growth — the 1RM estimate lets coaches prescribe exact weights rather than relying on vague RPE cues.

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Cardiac Rehabilitation Strength Training

Exercise physiologists use 1RM to safely prescribe resistance training for cardiac patients — training at 40–60% 1RM provides cardiovascular benefit with minimal haemodynamic stress.

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Athletic Strength Assessment

Strength and conditioning coaches test 1RM on the squat, bench press, and deadlift to benchmark athletes at the start of a season and track strength development across training blocks.

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Personal Training Programme Design

Personal trainers use 1RM estimates to prescribe evidence-based training loads for each client, replacing guesswork with specific weight targets matched to the client's current strength level.

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Strength Standards Benchmarking

Compare an athlete's 1RM to established bodyweight-relative strength standards (e.g., 2× bodyweight squat for advanced male) to classify current strength level and set realistic training goals.

Common Mistakes

Using too many reps for the prediction (> 10)

Most 1RM formulas are validated for sets of 1–10 reps. Above 10 reps, muscular endurance becomes a larger factor than maximal strength, causing the formula to significantly overestimate the true 1RM. For best accuracy, use a set of 3–6 reps.

Not performing a proper warm-up before testing

Testing 1RM (or a heavy submaximal set) without adequate warm-up increases injury risk and produces artificially low results. Warm up with progressively heavier sets at 50%, 70%, 85%, and 95% of expected 1RM before the test set.

Expecting the same formula to work for all exercises

Different exercises have different rep-to-max relationships. The Brzycki and Epley formulas were developed primarily for the bench press. They are less accurate for lower-body exercises (squat, leg press) and highly technical lifts (Olympic lifts) where fatigue patterns differ.

Using predicted 1RM percentages as precise prescriptions

70% of predicted 1RM is a starting point, not an exact prescription. Day-to-day readiness, fatigue, sleep, and nutrition all affect actual strength output. Use the 1RM-based load as the target and adjust by 2.5–5% based on how the warm-up feels.

Not updating the 1RM estimate regularly

A 1RM estimate made 8 weeks ago becomes increasingly inaccurate as training produces adaptation. Retest or recalculate the predicted 1RM at the start of each new training block (every 4–6 weeks) to ensure training loads remain appropriately challenging.

Training Intensity Zones by % 1RM

% of 1RM	Rep Range	Primary Adaptation
90–100%	1–3 reps	Maximal strength / neural adaptation
80–90%	3–5 reps	Strength-hypertrophy
70–80%	6–12 reps	Hypertrophy (muscle size)
60–70%	12–20 reps	Hypertrophy / muscular endurance
50–60%	20+ reps	Muscular endurance
< 50%	High reps	Active recovery / technique work

References

Brzycki, Matt. "Strength Testing — Predicting a One-Rep Max from Reps to Fatigue." JOHPERD, 1993.
Epley, Boyd. Poundage Chart. Boyd Epley Workout, 1985.
Baechle, T.R. and Earle, R.W. Essentials of Strength Training and Conditioning. NSCA/Human Kinetics, 2008.
Lombardi, V.P. Beginning Weight Training. W.C. Brown, 1989.
Mayhew, J.L. et al. "Accuracy of Prediction Equations for Determining One Repetition Maximum." Journal of Strength and Conditioning Research, 1995.