1RM Calculator

What Is a One-Rep Max?

Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. It is widely used in strength training to gauge overall strength on a given exercise and to structure workout programs around intensity zones.

Knowing your 1RM lets you assign precise percentages to your working sets, which removes guesswork and helps you train at the right intensity for your goal, whether that is building raw strength, adding muscle size, or improving muscular endurance.

How the Formulas Work

Rather than loading a barbell to its absolute maximum and risking injury, you can estimate your 1RM from a submaximal set. This calculator uses two of the most widely accepted prediction equations.

Epley Formula

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

The Epley formula is one of the most commonly cited equations in strength science. It tends to be especially accurate in the moderate rep range of 3 to 10 repetitions and is the default choice in many coaching and programming tools.

Brzycki Formula

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

The Brzycki formula was developed by Matt Brzycki and is sometimes considered slightly more conservative for lower rep counts. It tracks very closely with the Epley formula when reps are between 1 and 10 but may diverge at higher rep ranges. Comparing both results gives you a reliable confidence window for your true max.

How to Use This Calculator

Using the calculator is straightforward:

• Enter the weight you lifted in pounds or kilograms.
• Enter the number of reps you completed with that weight.
• The calculator instantly displays your estimated 1RM from both the Epley and Brzycki formulas, along with a percentage breakdown so you can plan your training loads.

For best results, use a recent set where you pushed close to failure or left only one to two reps in reserve. The closer the set is to true maximum effort, the more accurate the prediction will be.

Training with Percentages

Once you know your estimated 1RM, you can structure your training around percentage-based zones to target different adaptations:

• 90-100% of 1RM - Maximal strength. Sets of 1 to 3 reps for building peak force output.
• 80-89% of 1RM - Strength and power. Sets of 3 to 6 reps for developing heavy lifting capacity.
• 65-79% of 1RM - Hypertrophy. Sets of 6 to 12 reps, the primary range for muscle growth.
• 50-64% of 1RM - Muscular endurance. Sets of 12 to 20+ reps for work capacity and conditioning.

Most programs cycle through several of these zones over weeks or months to develop well-rounded strength and size. Recalculating your 1RM every few training blocks ensures your percentages stay current as you get stronger.

Tips for Accurate Estimates

• Use sets of 1 to 10 reps. Both formulas are most accurate within this range. Sets above 10 reps introduce more variables like cardiovascular fatigue and form breakdown that reduce prediction accuracy.
• Go close to failure. A set of 5 where you could have done 8 will underestimate your true max. Choose a weight that genuinely challenges you for the given rep count.
• Use consistent technique. Paused reps, touch-and-go reps, and bounced reps all produce different numbers. Keep your form the same each time you test.
• Test when fresh. Perform your estimation set early in the workout before fatigue accumulates. A fatigued set will give a lower and less accurate prediction.
• Re-test regularly. Strength changes over time. Updating your 1RM estimate every 4 to 8 weeks keeps your training percentages dialed in.