One-Rep Max Calculator: Estimate Your 1RM from Reps and Weight

The three formulas and when to use each

The Epley formula is 1RM equals weight times (1 plus reps divided by 30). It is the most widely used and is in most strength-training apps. Epley is slightly liberal: it estimates a 1RM that is about 1 to 2 percent higher than what most lifters can actually hit on a true 1RM test. For programming purposes this is fine because most coaches build a small buffer into prescribed percentages anyway.

The Brzycki formula is 1RM equals weight times 36 divided by (37 minus reps). It is more conservative than Epley and is the standard in some lifting circles, particularly military and law enforcement physical-readiness testing. Brzycki becomes less accurate above 10 reps because the denominator approaches zero.

The Lombardi formula is 1RM equals weight times reps raised to the 0.1 power. It is the simplest of the three and produces values between Epley and Brzycki for typical inputs (3 to 10 reps). Lombardi is rarely the first choice in modern programming but is useful when you want a third reading to triangulate.

For most lifters, use Epley as the default and try Brzycki as a sanity check. If the two formulas disagree by more than 5 percent of estimated 1RM, your test set was probably above 8 reps and the estimate is less reliable.

How to use 1RM for programming

Strength programs prescribe work in two units: absolute weight (load the bar with X) and relative weight (load the bar with Y percent of your 1RM). Relative programming is more flexible because it scales automatically as you get stronger and lets you re-test 1RM every 8 to 12 weeks to update the targets.

Typical training zones by percentage of 1RM:

Strength: 85 to 95 percent of 1RM for 1 to 5 reps. This is where neural adaptations are largest and where heavy compound lifts (squat, deadlift, bench, overhead press, weighted pull-up) drive progress.

Hypertrophy: 70 to 80 percent of 1RM for 6 to 12 reps. This is the standard bodybuilding rep range and produces the most muscle growth per unit of training stress for most people.

Endurance and metabolic: 55 to 70 percent of 1RM for 12 to 20+ reps. Builds work capacity and muscular endurance without producing as much hypertrophy.

De-load and movement quality: 40 to 60 percent for slower tempo and form work. Used in the lighter days of high-low training splits and during recovery weeks.

Limitations of 1RM estimation

The formulas were derived from population averages, but individual reps-to-1RM relationships vary by lift, training history, and limb-length leverages. The bench press tends to give the most accurate 1RM estimates from multi-rep sets; the deadlift tends to give the least accurate (deadlift 1RM is often higher than the estimate from a 5-rep max because deadlift falls off rapidly in fatigue). Olympic lifts (snatch, clean and jerk) are not well-suited to 1RM estimation from rep work because technique breakdown matters more than absolute strength.

For lifts you train regularly, recalibrate periodically by attempting a true heavy single (with safety equipment and a spotter for free-weight movements). The estimate becomes more useful as you build a personal sense of how your specific rep-strength curve relates to your true 1RM.

When to test versus estimate

True 1RM testing is appropriate for competitive lifters (powerlifting, weightlifting) and during specific testing weeks every 8 to 12 weeks for serious recreational lifters. The risk-reward of testing 1RM weekly is poor; missed lifts strain joints and connective tissue, and the central nervous system fatigue from a true 1RM attempt limits the rest of the week's training.

For most lifters, estimating 1RM from rep work every 4 to 6 weeks is sufficient. Test a heavy multi-rep set (3 to 5 reps) of a key lift, plug it into this calculator, and update your training percentages from the result.

What this calculator does not include

Lift-specific accuracy adjustments (some lifts estimate 1RM more reliably from multi-rep sets than others). Bar speed and velocity-based training estimates (which use bar speed at submaximal loads as a more accurate 1RM predictor than rep counts). Sex-based or age-based adjustments (the formulas are derived from general athletic populations). Fatigued versus fresh-state corrections. Powerlifting versus weightlifting differences. For weightlifters in the snatch and clean-and-jerk, use lift-specific tables that account for technique-driven rep dropoffs rather than the generic rep-based formulas here.