One-Rep Max Strength Calculator

One-rep max formulas explained and how to use training percentages

A one-rep max, commonly written as 1RM, is the maximum amount of weight a person can lift for exactly one full repetition with proper form. It is the standard measure of absolute strength in powerlifting and a widely used reference point in strength training programming. Knowing your 1RM for a given lift allows you to set percentage-based training loads precisely, rather than guessing or picking weights by feel.

Testing an actual 1RM requires performing a maximal effort lift, which carries a higher injury risk than submaximal training and requires a spotter for most exercises. For most athletes, it is safer and more practical to estimate the 1RM from a submaximal effort using a mathematical formula. You lift a challenging but manageable weight for somewhere between 1 and 10 reps, enter those values into the formula, and receive an estimated 1RM. The further you are from 1 rep, the less accurate the estimate tends to be; results from sets of 5 or fewer reps are generally more reliable than those from sets of 10 or more.

This calculator offers three formula options. The Epley formula, published in 1985, is one of the earliest and most widely used predictive equations. It calculates 1RM as weight multiplied by (1 plus reps divided by 30). It tends to overestimate slightly at higher rep counts but is acceptably accurate for sets in the 1 to 6 rep range. The Brzycki formula, developed by Matt Brzycki and published in 1993, calculates 1RM as weight multiplied by 36 divided by (37 minus reps). Brzycki performs well for low-to-moderate rep ranges and is commonly used in fitness education contexts. The Lander formula uses a more complex calculation: 1RM equals 100 times weight divided by (101.3 minus 2.67123 times reps). It was derived from empirical data and performs competitively with the other formulas across a range of rep counts.

No single formula is universally best. Each has been validated in different populations and contexts. The general recommendation is to choose one formula and use it consistently so that your estimated 1RM figures are comparable over time. Switching between formulas will produce slightly different numbers for the same performance, which makes progress tracking harder.

How to use training percentages from your 1RM

The primary value of knowing your estimated 1RM is that it allows percentage-based programming. Different training goals are associated with different percentage zones. Strength development generally occurs at 85 to 95 percent of 1RM with low rep counts of 1 to 5. Hypertrophy (muscle growth) is typically trained in the 65 to 85 percent range with moderate reps of 6 to 12. Muscular endurance work is done at lower percentages with higher rep counts.

The percentages shown in this calculator (90%, 85%, 80%, 75%, 70%) correspond to the weights you should load for different training purposes. For example, if your estimated 1RM on the squat is 150 kg, then 80 percent is 120 kg, which would be appropriate for sets of 6 to 8 reps focused on hypertrophy or strength-endurance work. At 90 percent (135 kg), you would be working in near-maximal territory suitable for low-rep strength sets.

Many structured strength programs use a concept called training max, which is a slightly reduced version of your true 1RM (often 90 percent of it) used as the base for percentage calculations. This builds in a margin of safety and ensures that the prescribed training loads are consistently achievable rather than occasionally beyond reach. If you are following a program that uses a training max, multiply the estimated 1RM from this calculator by 0.9 to get your training max, then apply the program's percentages from that figure.

Accuracy and safety notes

These formulas provide estimates only. Individual factors including neural efficiency, limb proportions, training history, fatigue level and lifting technique all affect how closely a predicted 1RM matches a tested one. For most purposes the estimate is close enough to be practically useful for programming. For competition or formal testing, an actual 1RM attempt supervised by a qualified coach is the only way to confirm a true maximum. Always use a spotter when lifting at or near maximal loads. This calculator does not account for accessory exercises, bodyweight movements, or cable machines where load does not directly correspond to a free-weight equivalent.