How to Estimate Your One-Rep Max (Epley and Brzycki)

Updated October 5, 2026 · General information, not medical advice.

You can estimate your one-rep max (1RM) from a hard set of a few reps, using a formula. The Epley formula is weight × (1 + reps ÷ 30), and the Brzycki formula is weight × 36 ÷ (37 − reps). Both work best on sets of about 10 reps or fewer, and both are estimates, not guarantees.

Want to skip the math? Use the one-rep max calculator.

What is a one-rep max?

Your one-rep max is the heaviest weight you can lift once with good form on a given exercise. It is a handy number for setting training weights as a percentage, and for tracking strength over time.

Testing a true max takes a long warm-up, spotters, and a lot of rest between tries. A formula lets you estimate it from a normal working set instead. That can feel less intimidating and takes less time, which is why these formulas are used [1].

The two common formulas

Both formulas take the weight you lifted and the reps you completed. Use a set taken close to failure, meaning you could not have done many more reps with good form.

Epley: 1RM = weight × (1 + reps ÷ 30) [2]

Brzycki: 1RM = weight × 36 ÷ (37 − reps) [3]

Worked example

You bench press 185 lb for 6 reps.

Epley: 185 × (1 + 6 ÷ 30) = 185 × 1.2 = 222 lb
Brzycki: 185 × 36 ÷ (37 − 6) = 185 × 36 ÷ 31 = about 215 lb

The two answers differ by a few pounds, which is normal. They are different curves fit to the same idea.

Another example

You squat 225 lb for 3 reps.

Epley: 225 × (1 + 3 ÷ 30) = 225 × 1.1 = about 248 lb
Brzycki: 225 × 36 ÷ 34 = about 238 lb

Why estimates get worse with more reps

The formulas are most trustworthy on lower-rep sets. A study of bench press in women noted that most equations function best with a load that produces 2 to 10 repetitions, and that the equations were more accurate when fewer than 10 repetitions to fatigue were used [1].

Why? A set of 15 or 20 reps depends a lot on muscular endurance, pacing, and how well you tolerate burning fatigue. Those traits vary from person to person and do not scale cleanly to a single heavy rep. Brzycki also gets unstable at high reps, because the number in the denominator (37 minus reps) gets small.

Other limits to keep in mind:

Different exercises behave differently. Equations are often built on specific groups, so they may over- or under-predict for you [1].
Different people behave differently. Age, sex, and training status may affect accuracy [1].
Effort matters. If you stopped well short of failure, the estimate will come out low.
Technique matters. Rep quality changes between sets. Count only reps with your normal form.

Liftrung's rule

Liftrung uses these rules for its estimates:

Epley is the default.
For sets of 6 to 10 reps, it averages Epley and Brzycki.
Reps are capped at 12, and results above that are marked approximate.

Reps are capped at 12 because estimates get less accurate with higher reps, and results above that are marked approximate.

How to use your estimate

Track the trend, not one number. A single estimate can bounce around. A rise over several weeks is the signal.
Compare like with like. Use similar rep ranges when you compare sessions.
Do not test a real max just because the number says you can. Use the estimate to pick sensible working weights.
Use percentages cautiously. A given percentage of 1RM does not produce the same reps for every person, so adjust to how the set feels.

Doing this in Liftrung

Liftrung shows an estimated 1RM from your logged sets, using the rule above. It also shows what you did last time beside every set, and an estimated one-rep max trend for each lift, so you can see whether the estimate is moving up.

Key points

Epley: weight × (1 + reps ÷ 30). Brzycki: weight × 36 ÷ (37 − reps).
Use a hard set of 10 reps or fewer. Accuracy falls as reps climb [1].
Treat the result as an estimate, and watch the trend over weeks.
Liftrung uses Epley, averages Epley and Brzycki for 6 to 10 reps, and caps reps at 12, marking those results approximate.

Sources

Mayhew JL, Johnson BD, LaMonte MJ, Lauber D, Kemmler W. Accuracy of prediction equations for determining one repetition maximum bench press in women before and after resistance training. J Strength Cond Res, 2008;22(5):1570-1577. https://www.unm.edu/~rrobergs/478PredictionAccuracy.pdf
Epley B. Poundage chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises, 1985. (Print publication; not independently verified here.)
Brzycki M. Strength testing: predicting a one-rep max from reps-to-fatigue. J Phys Educ Recreat Dance, 1993;64(1):88-90. https://doi.org/10.1080/07303084.1993.10606684