One Rep Max (1RM) Calculator

Free One Rep Max (1RM) Calculator

Calculate your one rep max (1RM) with our free weightlifting calculator. Find out the maximum weight you can lift for a single repetition based on your performance with multiple reps. Our calculator uses proven formulas like Brzycki, Epley, and others to give you accurate strength estimates without testing your true max.

What is a One Rep Max (1RM)?

Your one rep max (1RM) is the maximum weight you can lift for a single repetition of an exercise. It's a key strength measurement used by powerlifters, bodybuilders, and fitness enthusiasts to track progress and plan training programs.

Your one rep max (1RM) is more than just bragging rights. It's the foundation of effective strength programming. Our strength calculator lets you know how you're progressing in the gym, helps you plan workout programs effectively using percentages of your max, and allows you to change rep ranges with confidence. Calculating your 1RM with our weightlifting calculator is essential for tracking strength progress and optimizing your training.

In the Gravitus app, we compute all of your one rep maxes on the fly as you're working out using the Brzycki formula. We'll let you know the instant you hit a personal record (PR) whether you were doing a max one rep effort or working with higher rep ranges. With this calculator, you can quickly estimate your 1RM for any exercise without having to test your true maximum weight, which can be risky without proper supervision.

Calculate Your One Rep Max (1RM)

Units

Imperial (lbs) Metric (kg)

Reps

Weight lbs

Formula

The Brzycki formula is the standard used by Gravitus for consistency.

The formulas used to calculate 1RM are less accurate at higher rep ranges (above 10 reps). Results may vary.

Your One Rep Max

This is the maximum weight you should be able to lift for a single rep based on your input.

Estimated Rep Max Values

Based on your calculated 1RM and the selected formula, here are your estimated rep max values:

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How Our One Rep Max (1RM) Calculator Works

This one rep max calculator provides an estimation of your one rep max based on the weight you can lift for multiple repetitions. Our 1RM calculator is the perfect tool for lifters who want to know their max without the risk of testing a true 1RM. By default, we use the Brzycki formula, which is also used in the Gravitus app for consistency. This formula is widely respected in the strength training community for its accuracy, especially in the 1-10 rep range, making our max calculator reliable for strength athletes of all levels.

Brzycki Formula (Default)

1RM = weight × (36 / (37 - reps))

The Brzycki formula is our default and the one used by the Gravitus app. It tends to be most accurate in the 5-10 rep range and is widely used in strength training programs.

While we default to the Brzycki formula, our calculator also allows you to select from other popular formulas. Each formula may give slightly different results based on their unique mathematical approach:

Epley Formula

weight × (1 + reps/30)

Lander Formula

(100 × weight) / (101.3 - 2.67123 × reps)

Lombardi Formula

weight × (reps ^ 0.1)

O'Conner Formula

weight × (1 + 0.025 × reps)

Mayhew Formula

(100 × weight) / (52.2 + 41.9 × e^(-0.055 × reps))

Wathan Formula

(100 × weight) / (48.8 + 53.8 × e^(-0.075 × reps))

All these formulas aim to predict your 1RM, but they may give different results. For consistent tracking in the Gravitus app, we always use the Brzycki formula. For most accurate results with any formula, we recommend using rep ranges of 10 or less.

How to Use 1RM in Your Training

Track Progress

Monitor strength improvements over time

Set Percentages

Plan precise training weights based on percentages of 1RM

Compare Rep Ranges

Understand strength equivalents across different rep schemes

Compare with Others

See how you stack up against other lifters

You can learn more about one rep max calculations and the scientific basis for these formulas here.

Frequently Asked Questions About One Rep Max (1RM)

A 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's considered the gold standard for measuring maximal strength in weightlifting and is commonly used in strength training programs to track progress and determine appropriate working weights.

Testing your true 1RM can be risky, especially for beginners or when performed without proper supervision. The heavy loads used during a 1RM attempt put significant stress on your joints, muscles, and central nervous system and carry an increased risk of injury. That's why many coaches and fitness professionals recommend using calculators like this one to estimate your 1RM based on performance at higher rep ranges.

One rep max calculators provide estimates, not exact measurements. Their accuracy varies based on several factors including the specific exercise, your experience level, and the rep range used for calculation. Most formulas are more accurate when using weights you can lift for 1-5 reps and become less precise with higher rep counts (10+ reps). The Brzycki formula used by Gravitus tends to be reliable for most individuals, particularly in the 5-10 rep range.

For most recreational lifters, calculating your 1RM every 4-6 weeks is sufficient to track progress. More frequent testing can interfere with your regular training program and may not show meaningful changes. Competitive powerlifters and Olympic weightlifters might test more frequently as they approach competitions. The Gravitus app automatically calculates your 1RM for every set and tracks your progress over time without requiring dedicated testing sessions.

Once you know your 1RM, you can use percentages to plan your working sets. For example, working sets for strength development typically range from 70-85% of your 1RM for 3-5 reps, while hypertrophy (muscle building) work often falls in the 65-75% range for 8-12 reps. Knowing your 1RM allows you to precisely calculate these working weights for optimal training stimulus.

Different 1RM formulas were developed using data from different populations (powerlifters, college athletes, etc.) and may have been optimized for specific rep ranges or exercises. Each formula uses a unique mathematical relationship between reps and weight to predict 1RM, which leads to variations in the results. Gravitus uses the Brzycki formula consistently to ensure your progress tracking remains comparable over time.

While 1RM calculators can be used for most resistance exercises, they tend to be most accurate for compound movements like squats, deadlifts, bench press, and overhead press. They may be less accurate for isolation exercises or movements that rely heavily on technique or flexibility rather than pure strength.

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