Data Source and Methodology

The ability to predict a one-rep max (1RM) is a cornerstone of strength programming. This calculator uses scientifically validated and peer-reviewed formulas developed by leaders in exercise science. We do not use proprietary or unverified calculations.

The primary sources for the formulas are:

  • Brzycki, M. (1993). Strength Testing-Predicting a One-Rep Max from Reps-to-Fatigue. Journal of Physical Education, Recreation & Dance, 64(1), 88-90.
  • Epley, B. (1985). Poundage Chart. Boyd Epley. University of Nebraska.
  • Lander, J. (1985). Maximums based on reps. National Strength and Conditioning Association Journal, 6(6), 60-61.

All calculations are based strictly on the formulas provided by these sources.

The Formulas Explained

While all formulas aim to predict your 1RM, they use slightly different mathematical models. No formula is perfect, but they provide a safe and reliable estimate without requiring a risky maximal-effort lift.

Brzycki Formula

\\[ 1RM = \frac{Weight}{1.0278 - (0.0278 \times Reps)} \\]

This is one of the most widely used and validated formulas, common in both academic and athletic settings.

Epley Formula

\\[ 1RM = Weight \times \left(1 + \frac{Reps}{30}\right) \\]

The Epley formula is another popular model, often favored for its simplicity and accuracy, particularly with experienced lifters in lower rep ranges (2-6).

Glossary of Variables

Weight Lifted
The total weight (in kg or lbs) you successfully lifted for your set. This should be the weight on the bar, including the bar itself.
Repetitions (Reps)
The number of successful repetitions you completed in a single set before reaching muscular failure. This calculator is not accurate for 1 rep (as that is your 1RM) or for very high reps (over 12-15).
Estimated 1RM
The predicted maximum weight you could lift for a single, all-out repetition.
Training Zone
A specific percentage of your 1RM used to target a particular fitness goal (e.g., strength, hypertrophy, endurance). The included chart and table show you what weight to use for different goals.

How It Works: A Step-by-Step Example

Let's walk through a real-world scenario to see how the calculation is made.

  • Scenario: An athlete performs a set of squats.
  • Input Weight: 100 kg
  • Input Reps: 5
  • Selected Formula: Epley

The calculator applies the Epley formula:

  1. Formula: \\( 1RM = Weight \times (1 + \frac{Reps}{30}) \\)
  2. Insert values: \\( 1RM = 100 \times (1 + \frac{5}{30}) \\)
  3. Calculate fraction: \\( \frac{5}{30} = 0.1667 \\)
  4. Add to 1: \\( 1 + 0.1667 = 1.1667 \\)
  5. Final calculation: \\( 1RM = 100 \times 1.1667 = 116.7 \\)

Result: The athlete's estimated 1RM for the squat is 116.7 kg. The results table would then show weights like 99.2 kg (85% for hypertrophy) and 87.5 kg (75% for volume).

Frequently Asked Questions (FAQ)

Which 1RM formula is the most accurate?

There is no single "most accurate" formula. Accuracy depends on the individual, their training experience, muscle fiber type, and the exercise. The Epley and Brzycki formulas are the most researched and generally considered reliable. We recommend trying both and seeing which one aligns best with your perceived exertion.

Is this calculator accurate for all exercises?

These formulas are most accurate for large, compound exercises like the **squat, bench press, and deadlift**. They are less accurate for isolation exercises (e.g., bicep curls) or complex Olympic lifts (e.g., snatch) which have a higher technical skill component.

Why are the formulas inaccurate for high reps (e.g., 20+)?

Once you go beyond 10-12 reps, the limiting factor can shift from pure maximal strength to muscular endurance and cardiovascular fitness. The mathematical relationship between strength and endurance breaks down at high rep ranges, making 1RM predictions unreliable.

How do I use the 'Training Zones' results?

The training zones table is your guide for programming. Based on your goal, you would select a percentage and rep range:

  • Max Strength: 90-100% 1RM (1-3 reps)
  • Strength/Hypertrophy: 80-90% 1RM (4-6 reps)
  • Hypertrophy (Muscle Size): 70-80% 1RM (8-12 reps)
  • Muscular Endurance: 60-70% 1RM (12-15+ reps)

Use the weight in the table that corresponds to your goal.

Is it safe to test my 1RM directly?

Testing a "true" 1RM (i.e., actually lifting the maximal weight) carries a high risk of injury, especially for non-competitive or inexperienced lifters. It requires a proper warm-up, spotters, and perfect form. This calculator provides a much safer way to estimate your 1RM to guide your training.

My reps were 1. The calculator just showed my weight.

This is correct. If you successfully lift a weight for exactly one repetition, that *is* your one-rep max (1RM) by definition. The prediction formulas are only needed when you perform 2 or more repetitions.

Tool developed by Ugo Candido.
Content and methodologies verified by Dr. Jane Wescott, CSCS (Certified Strength and Conditioning Specialist).

Last accuracy review: