One-Rep Max (1RM) Calculator

About the One-Rep Max (1RM) Calculator

Testing a true one-rep max (1RM) means attempting the heaviest single lift you can manage — slow, tiring and riskier than an ordinary set. Prediction equations estimate it from a submaximal set instead: enter the weight and the reps you did (1–12) and this calculator runs the seven equations compared by LeSuer and colleagues — Epley, Brzycki, Lombardi, Mayhew, O’Conner, Wathen and Lander — and shows each result and their average.

If you stopped short of failure, say how many more reps you had left (reps in reserve, or the matching RPE) and the set is counted as reps to failure. You also get a %1RM training table and a rep-max table rounded to the plates you have, in kg or lb. Everything is calculated in your browser.

The seven equations

With w the weight lifted and r the reps to failure:

• Epley: 1RM = w × (1 + r ÷ 30)
• Brzycki: 1RM = w × 36 ÷ (37 − r)
• Lombardi: 1RM = w × r^0.10
• Mayhew et al.: 1RM = 100 × w ÷ (52.2 + 41.9 × e^(−0.055 × r))
• O’Conner et al.: 1RM = w × (1 + 0.025 × r)
• Wathen (sometimes spelled Wathan): 1RM = 100 × w ÷ (48.8 + 53.8 × e^(−0.075 × r))
• Lander: 1RM = 100 × w ÷ (101.3 − 2.67123 × r)

A single rep to failure is the 1RM itself, so for r = 1 the calculator uses the weight lifted as the 1RM; the equations themselves would add up to about 9% (Mayhew) at one rep, and only Brzycki and Lombardi return the weight exactly. The calculator shows the average of the seven as the headline estimate; the spread between them is a reminder that each is only an estimate.

Reps in reserve and RPE

The RIR-based RPE scale (Zourdos et al.) ties each rating to the reps you could still have done: RPE 10 = 0 reps in reserve, RPE 9 = 1, RPE 8 = 2, RPE 7 = 3, with half points such as 8.5 for “1–2 more”. A set of 5 at RPE 8 is therefore treated as 7 reps to failure.

The scale’s authors chose rep-in-reserve descriptions for RPE 5–10 because lifters judge their remaining reps more accurately close to failure; in an earlier study they cite, bodybuilders’ estimates of their remaining reps closely matched the reps they actually did. That is why the calculator stops at 3 reps in reserve: the further from failure, the more the estimate depends on guesswork.

How the training tables are worked out

The %1RM table multiplies the estimated 1RM by each percentage, then rounds to your plate step (2.5 kg or 5 lb by default; choose 1.25 kg if you have fractional plates). The approximate reps beside each percentage come from the same average curve, so they are estimates too — at 70% and below the equations predict more than 12 reps, where they are least reliable.

The rep-max table asks the reverse question: what could you lift for exactly n reps? It divides the 1RM by the average of the seven equations’ factors for n reps, so at the reps you actually did it gives back the weight you lifted.

How accurate are 1RM predictions?

Studies of these equations have often found poorer accuracy when the test set allowed 10 or more repetitions, and accuracy also depends on the exercise, training status, age and sex. LeSuer et al. found, for example, that the Mayhew equation underestimated the 1RM in the deadlift by about 10%. Use the estimate to choose training loads, not as a measured max — and if you do test a true 1RM, warm up thoroughly and use a spotter or safety arms.

Sources

• LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. J Strength Cond Res 11(4):211-3 — the seven equations as reproduced by Lin et al., Sci Rep 11:9137 (PMC8080630, Table 1)
• Epley B. Poundage Chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises, 1985
• Brzycki M. Strength testing — predicting a one-rep max from reps-to-fatigue. JOPERD 64(1):88-90
• Zourdos MC et al. Novel resistance training-specific rating of perceived exertion scale measuring repetitions in reserve. J Strength Cond Res 30(1):267-75
• Helms ER, Cronin J, Storey A, Zourdos MC. Application of the repetitions in reserve-based rating of perceived exertion scale for resistance training. Strength Cond J 38(4):42-9
• Bohman T et al. Concurrent validity of an isokinetic lift test used for admission to the Swedish Armed Forces. PLoS One 13(11):e0207054 (summarising LeSuer et al. on the deadlift) · Mitter B et al. Reproducibility of strength performance and strength-endurance profiles. PLoS One 17(5):e0268074 (accuracy at 10 or more reps) · Yan H et al. J Hum Kinet 102:159-71 (factors affecting accuracy)

Limitations

• Every equation is an estimate; your real 1RM may be several percent higher or lower, and more so for sets of 10 or more reps.
• Use a set taken to (or close to) failure with good form; a set stopped far from failure underestimates your strength.
• Equations were developed mostly in the bench press and squat; the deadlift and other lifts may differ.
• Weights up to 600 kg (1,320 lb), 1–12 reps and 0–3 reps in reserve are accepted.

Privacy

Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.