1RM Calculator

What is a one-rep max (1RM)?

A one-rep max (1RM) is the maximum weight an individual can lift for a single repetition of an exercise with correct technique. It is the standard benchmark for absolute strength across powerlifting, Olympic weightlifting, strength & conditioning research, and evidence-based programming. 1RM is typically reported for compound lifts — squat, bench press, deadlift, overhead press — where it reflects neuromuscular capacity and inter-muscular coordination under maximal load. Because repeated true 1RM attempts carry injury risk and require full recovery between sessions, most lifters estimate 1RM from sub-maximal sets instead. The National Strength and Conditioning Association (NSCA) recommends estimation via established predictive formulas for general programming, reserving actual 1RM testing for competition preparation and periodized peaking cycles. Estimated 1RM is used to prescribe training percentages, track progress between testing blocks, and calibrate autoregulated programs.

How to estimate your 1RM safely

To estimate a 1RM from a sub-maximal set, choose a weight that lets you complete 3–6 strict repetitions with one rep left in reserve. Record the weight and the reps completed, then apply one of the predictive formulas. Example: if you bench press 100 kg for 5 clean reps using the Epley formula, estimated 1RM = 100 × (1 + 5/30) = 100 × 1.167 = 116.7 kg. The 3–6 rep range is the accuracy sweet spot — fewer reps leave more room for set-to-set variance, while more reps introduce fatigue and cardiovascular limitations that inflate estimates. Warm up with progressive sets (40%, 60%, 75%, 85%) before the working set. Reps must be performed to true muscular fatigue, not a self-selected stopping point. If you stopped with 3+ reps in reserve, the estimate will understate your actual strength.

Epley vs Brzycki vs Lombardi formulas

Several 1RM prediction formulas exist, derived from different datasets between 1978 and 1995. Epley's formula (1985) is the most widely used: 1RM = weight × (1 + reps/30). It tends to predict conservatively at very low reps and slightly overestimate above 10 reps. Brzycki's formula (1993) is 1RM = weight / (1.0278 − 0.0278 × reps) and produces nearly identical results to Epley for sets of 1–6 reps, then diverges. Lombardi's formula (1989) is 1RM = weight × reps^0.10, which flattens out differently and sometimes produces lower estimates. For sets of 1–5 reps, all three formulas agree within 2–3%. A 2017 systematic review in the Journal of Strength and Conditioning Research found no single formula is universally most accurate — individual variation in neuromuscular profile matters more than the choice of formula.

When should you actually test your 1RM?

True 1RM testing is appropriate for competitive powerlifters before a meet, intermediate-to-advanced trainees at the end of a peaking block, and strength & conditioning staff evaluating athletes. For everyone else, estimated 1RMs are more useful than measured ones. Actual testing requires full recovery (48+ hours of light training), a progressive warm-up that primes the nervous system without creating fatigue (8–10 ramp-up sets), and 3–5 minutes between top attempts. A competition-style protocol uses three attempts: opener at 92–94% of estimated 1RM, second at 96–98%, third at 100–102% if the previous two went smoothly. Testing more frequently than every 8–16 weeks yields diminishing returns — the nervous-system cost is high, and day-to-day performance variance of ±3–5% makes small numerical differences noisy. Track estimated 1RMs from working sets instead for better progress signal.

How to use 1RM for training (percentages and RPE)

Training load is typically prescribed as a percentage of 1RM. Rough guidelines: 60–70% 1RM for technique work and warm-ups; 70–80% 1RM for hypertrophy (6–12 reps); 80–90% 1RM for strength (3–5 reps); 90–100% 1RM for peaking or testing (1–3 reps). Most evidence-based programs combine percentage-based prescriptions with Reps in Reserve (RIR) or Rate of Perceived Exertion (RPE) autoregulation, which adjusts load based on daily readiness. A set at 80% 1RM should correspond roughly to RPE 8 (2 reps in reserve) for most exercises. If the prescribed percentage feels consistently harder or easier than expected, your true 1RM has likely drifted and an estimate-refresh from a working set is warranted. Prime Progression tracks estimated 1RM automatically after every logged set.