One Rep Max Calculator
Find your theoretical one-rep maximum from a submaximal lift using four established strength formulas. Use the result to set training percentages for powerlifting, strength, or hypertrophy programs.
About this calculator
A one-rep max (1RM) is the heaviest weight you can lift for exactly one full repetition with proper form. Because testing true 1RM carries injury risk, several predictive formulas extrapolate it from submaximal efforts. The Epley formula is: 1RM = weight × (1 + reps / 30). The Brzycki formula is: 1RM = weight × 36 / (37 − reps). The McGlothin formula is: 1RM = weight × (1 + 0.025 × reps). The Lombardi formula uses: 1RM = weight × reps^0.10. All four formulas assume a linear or near-linear relationship between load and repetitions to fatigue. Accuracy is highest when the set uses 2–10 reps; estimates become less reliable above 15 reps because fatigue and muscular endurance start to dominate. The calculator then multiplies the estimated 1RM by a chosen training percentage to output the target load for a given intensity zone.
How to use
Example: You bench press 185 lbs for 5 reps using the Epley formula at 80% training percentage. Step 1: 1RM = 185 × (1 + 5 / 30) = 185 × 1.1667 ≈ 215.8 lbs. Step 2: Apply training percentage: 215.8 × 0.80 ≈ 172.6 lbs, rounded to 173 lbs. That is your target working weight for an 80% intensity set. For a hypertrophy block (65–75%) you would use 140–162 lbs, and for near-maximal strength work (90–95%) you would load approximately 194–205 lbs.
Frequently asked questions
Which one-rep max formula is the most accurate for powerlifting?
Research suggests the Brzycki and Epley formulas perform similarly well for sets of 2–6 reps, which is the typical powerlifting training range. The Brzycki formula tends to be slightly more conservative and is preferred by many coaches for competition peaking cycles. The Epley formula is more commonly used in general strength training software. All formulas lose accuracy above 10 repetitions, so testing with a heavier, lower-rep set always produces a more reliable estimate.
How should I use my one-rep max to structure a strength training program?
A standard strength periodization model assigns different rep ranges to different percentages of your 1RM. Heavy strength work (1–3 reps) typically uses 90–100% of 1RM, power and strength (3–5 reps) uses 80–90%, hypertrophy (6–12 reps) uses 65–80%, and muscular endurance (15+ reps) drops below 65%. Programs like 5/3/1 and Conjugate Method explicitly build their loading schemes around 1RM percentages. Recalculate your 1RM every 4–8 weeks as you progress to keep training percentages accurate.
How many reps should I use to get the most accurate one-rep max estimate?
The most accurate predictions come from sets of 3–6 reps taken close to failure. Sets in this range minimize the influence of muscular endurance and keep the fatigue component small enough that force output remains near-maximal. Sets above 10 reps introduce significant endurance variability, which causes most formulas to overestimate the true 1RM by 5–15%. If you can only safely test at higher rep ranges, the Lombardi formula (reps^0.10) handles higher-rep sets slightly better than the others.