One Rep Max (1RM) Calculator

A "one rep max" (one-repetition maximum) is the maximum weight a person can lift for one complete repetition of a specific exercise while maintaining proper form. It is a measure that is commonly used in weightlifting competitions since it represents the peak force that a person's muscles can generate in an all-out effort.

A person's one rep max typically differs based on the exercise, whether it be a bench press, squat, deadlift, overhead press, or whatever other exercise is being performed. Thus, it is important to measure a one rep max for a given exercise rather than applying a one rep max in one exercise to other exercises.

Several formulas have been developed to estimate your one rep max based on the weight you can lift for multiple repetitions. Each formula has its own strengths and may be more accurate for different individuals or exercises.

Brzycki Formula

Developed by Matt Brzycki, this formula tends to be accurate for repetitions under 10 and is commonly used for bench press and squat exercises:

$$1RM = \frac{w}{1.0278 - 0.0278 \times r}$$

Epley Formula

Created by Boyd Epley, this is one of the most widely used formulas and tends to give slightly higher estimates than other methods:

$$1RM = w \times (1 + 0.0333 \times r)$$

Lombardi Formula

Developed by Gordon Lombardi, this formula uses an exponential relationship between repetitions and maximum strength:

$$1RM = w \times r^{0.1}$$

Where w is the weight lifted and r is the number of repetitions performed.

1. Enter the weight you can lift (kg or lb) for a given exercise.
2. Input the number of repetitions you can perform with this weight (between 1-10 for most accurate results).
3. Select your preferred calculation method or use the average of all methods.
4. Click the Calculate button to see your estimated one rep max and percentage breakdowns.

For the most accurate estimate, use a weight that you can lift between 1 and 10 times. The accuracy decreases as the number of repetitions increases beyond 10.

Strength Training Programs: Many strength training programs are based on percentages of your 1RM. Knowing your 1RM allows you to accurately follow these programs without having to actually attempt a maximum lift each time.

Tracking Progress: By periodically estimating your 1RM, you can track your strength gains over time, even if you're not regularly attempting maximal lifts.

Safety: Attempting a true 1RM can be risky, especially for beginners. Using these formulas gives you a good estimate without the safety risks associated with maximal lifting attempts.