1rm Calculator

1RM Strength Calculator

Note: Best accuracy is between 1-10 reps.

A One Rep Max (1RM) is the maximum amount of weight you can lift for a single repetition of a specific exercise with proper form. It is considered the gold standard for measuring absolute strength in powerlifting, weightlifting, and general strength training.

How This Calculator Works

This tool uses the Brzycki Formula, which is widely recognized as one of the most accurate equations for estimating strength based on sub-maximal efforts. The formula used is:

1RM = Weight / (1.0278 – (0.0278 × Reps))

By performing a set to failure (usually in the 3–8 rep range), you can safely estimate your max without the high injury risk associated with true 1RM testing.

Why Calculate Your 1RM?

• Program Design: Most strength programs (like 5/3/1 or Starting Strength) prescribe weights based on a percentage of your 1RM.
• Tracking Progress: Comparing your estimated 1RM over months allows you to see strength gains even if you aren't testing maxes frequently.
• Objective Loading: It removes the guesswork from your training, ensuring you are lifting heavy enough to stimulate muscle growth and strength adaptations.

Practical Example

If you bench press 185 lbs for 8 reps, the calculator estimates your 1RM at approximately 230 lbs. Based on this, if your workout plan calls for 75% intensity, you would load the bar with 172.5 lbs.

1RM Percentages and Training Goals

Depending on your fitness goals, you should train at different percentages of your 1RM:

• Power: 1–5 reps at 85%–100% 1RM
• Hypertrophy (Muscle Growth): 8–12 reps at 65%–80% 1RM
• Endurance: 15+ reps at below 60% 1RM

Safety Disclaimer

Attempting a true 1RM test should only be done by experienced lifters with proper spotters and safety equipment (like a power rack). For beginners and intermediate lifters, using this 1RM calculator is a significantly safer alternative to find your lifting limits.