What is a One-Rep Max (1RM)?

Your one-rep max is the absolute maximum amount of weight you can lift for a single repetition of a given exercise with proper form. It is the standard measure of an individual's maximal strength.

Is it safe to test my true 1RM?

Testing a true 1RM carries a significant risk of injury, especially for beginners or those without a spotter. Using a 1RM calculator is a much safer alternative, as it allows you to estimate your max strength by lifting a lighter, 'sub-maximal' weight for multiple reps.

Which formula is the most accurate?

No formula is perfect, but the Brzycki formula is widely considered the most accurate, especially for repetitions under 10. The Epley formula is also very popular. The best approach is to pick one formula and use it consistently to track your progress.

One-Rep Max (1RM) Calculator

CRITICAL SAFETY WARNING: This calculator provides an estimate of your max lift. Never attempt a true one-rep max without proper training, a spotter, and a safe environment. Lifting maximal weight carries a high risk of injury. Always prioritize proper form.

Your Estimated One-Rep Max (1RM) is:

Training Percentages

Use these percentages of your 1RM to structure your workouts:

Percentage	Weight	Typical Rep Range for Goal

How is One-Rep Max Calculated?

A one-rep max (1RM) is the most weight you can lift for one full repetition of an exercise. Directly testing your 1RM can be risky, so formulas have been developed to estimate it based on a "sub-maximal" effort (lifting a lighter weight for multiple reps).

This calculator uses several popular formulas:

Brzycki: The most widely used formula, developed by Matt Brzycki. It's generally considered most accurate for reps below 10.
Epley: Another very common formula, developed in 1985. It's simple and effective across various rep ranges.
Lander & Lombardi: Other scientifically validated formulas that provide slightly different estimates.

The best practice is to choose a weight you can lift for 2-8 reps with good form. This range provides the most reliable input for an accurate 1RM estimation.

The Surprising History of the 1RM

The concept of a one-repetition maximum wasn't just born in a gym; it grew out of sports science and the need to safely measure strength. In the 1980s, coaches and researchers, particularly in American football, needed a way to assess their athletes' strength without the constant risk of injury from max-out attempts.

Pioneers like Matt Brzycki (at Princeton University) and Boyd Epley (at the University of Nebraska) were instrumental. They collected data from thousands of lifts and developed predictive equations. Their goal was to find a reliable mathematical relationship between the weight an athlete could lift for several reps and their theoretical single-rep max. These formulas revolutionized strength training, making it safer and more scientific for athletes and the general public alike.

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Frequently Asked Questions (FAQ)

How can I use my 1RM for training?

Percentage-based training is a popular way to use your 1RM. You structure your workouts using percentages of your 1RM to target specific goals. For example: Strength (85-95% of 1RM for 2-5 reps), Hypertrophy/Muscle Growth (70-85% of 1RM for 6-12 reps), or Endurance (50-70% of 1RM for 12+ reps). Our percentages table gives you a great starting point.

How often should I recalculate my 1RM?

For most people, re-testing or recalculating your 1RM every 4 to 8 weeks is a good cadence. This allows enough time for your training to result in meaningful strength gains. If you are a beginner, you may be able to see progress more quickly.

Why is my calculated 1RM different between formulas?

Each formula uses a slightly different mathematical model to predict the 1RM. It's normal to see small variations. The key is not the exact number but consistency. Choose one formula (Brzycki is a great default) and stick with it to accurately track your progress over time.