How to Estimate Your One-Rep Max Without Testing It

Your one-repetition maximum (1RM) is the heaviest load you can lift once with good form. Testing it directly is tiring and carries more risk of injury, so most lifters estimate it from a heavier set of several repetitions. The equations are simple and work well for hard sets of up to about 10 reps; they get less reliable the more reps you do and the further from failure you stop.

This article is general information, not medical advice.

The Equations

The two most used:

• Brzycki (1993): 1RM = load × 36 ÷ (37 − reps)
• Epley: 1RM = load × (1 + reps ÷ 30)

For 100 kg lifted 5 times, Brzycki gives 112.5 kg and Epley about 116.7 kg. They agree closely at low reps and drift apart as reps rise. Brzycki proposed his equation for sets of up to 10 repetitions, and a set of one gives back the load itself.

Why Hard Sets of 10 or Fewer

The equations assume the set was close to the most reps you could do with that load. A set of 5 where you could have done 8 tells the equation you’re weaker than you are. That’s why estimates are best taken from your top sets, the heaviest you did that day, taken close to failure.

High-rep sets add more error, since endurance as well as strength decides how many reps you get at a lighter load. A heavy triple predicts a single better than a set of 15.

Lifts differ too. When LeSuer and colleagues tested seven equations against measured maximums in 67 college students, the estimates correlated closely with the real thing for the bench press, squat, and deadlift alike, but every equation underestimated the deadlift on average. So compare estimates for the same lift, not across lifts.

Using the Estimate Well

• Use it as a trend. An estimated 1RM that rises over weeks from the same kind of top set is good evidence you’re stronger, without ever testing a single.
• Record how hard the set was. Reps in reserve (RIR), how many more you could have done, tells you whether a set was close enough to failure for the estimate to mean much; see What Are RPE and Reps in Reserve?
• Test a true single occasionally, if your training calls for it, with a spotter or safety bars, after a thorough warm-up. A tested max is simply a set of one.

Following It in Kaizora

You log strength training set by set on Fitness: the exercise, reps, load, RPE, and whether it was a warm-up, a drop set, or a set to failure. From every working set of the back squat, bench press, or deadlift, Kaizora calculates an estimate by Brzycki’s equation, counting the reps you had left in reserve by the set’s RPE (a set at RPE 8 of 5 reps counts as 7, and a set without an RPE as taken to failure), from sets of 10 or fewer reps so counted: Estimated Back Squat One-Repetition Maximum, Estimated Bench Press One-Repetition Maximum, and Estimated Deadlift One-Repetition Maximum. Warm-ups give no estimate. Each estimate’s page shows your personal best, so a new best set stands out. Sets close to failure still give the most reliable values, since reps in reserve are a guess.

The Short Version

• Brzycki: 1RM = load × 36 ÷ (37 − reps); Epley: load × (1 + reps ÷ 30).
• They’re reliable for hard sets of 10 reps or fewer, taken near failure.
• Follow the estimate from your top sets over time rather than any single value.

Sources

• Brzycki M, “Strength testing: predicting a one-rep max from reps-to-fatigue,” Journal of Physical Education, Recreation & Dance 64, no. 1 (1993): 88–90. doi:10.1080/07303084.1993.10606684
• LeSuer DA et al., “The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift,” Journal of Strength and Conditioning Research 11, no. 4 (1997): 211–213. doi:10.1519/00124278-199711000-00001