What Is a One-Rep Max (1RM)? How to Estimate It | Strongbro
Quick answer
A one-rep max (1RM) is the heaviest weight you can lift once, through a full range of motion, on a given exercise. It is the standard unit of strength in a training log. Testing one costs a whole session, so it is usually estimated instead, from a submaximal set and a formula such as Brzycki, where 80 kg for 8 reps predicts a 1RM of about 99 kg. Tracked over months, that estimate shows whether you are getting stronger.
The one-rep max is the heaviest weight you can lift once on a given exercise, through a full range of motion. It ends up being the number the rest of your log is measured against: program percentages are written as fractions of it, personal records are ranked by it, and the question of whether you are stronger than you were in March is answered with it.
Two ways to get the number
You can test it or estimate it. Testing means warming up, adding weight in small jumps, and finding the heaviest single you can complete with good form. Estimating means taking a set of several reps and running it through a prediction formula. Two formulas cover most of the field.
Brzycki divides the weight by a factor that shrinks as the reps go up:
1RM = weight ÷ (1.0278 − 0.0278 × reps)
Epley multiplies the weight by a factor that grows with the reps:
1RM = weight × (1 + reps ÷ 30)
Take a set of 80 kg for 8 reps.
- Brzycki: 80 ÷ (1.0278 − 0.2224) = 80 ÷ 0.8054 = 99.3 kg
- Epley: 80 × (1 + 8 ÷ 30) = 80 × 1.267 = 101.3 kg
Two kilograms apart, which is less than the smallest plate in most gyms. The two formulas cross at 10 reps, where both return 106.7 kg for 80 kg × 10. Below that Epley reads slightly higher; above it, Brzycki does.
The estimate is most trustworthy from sets of 2 to 6 reps, still useful up to 10, and increasingly a guess past 12, where the thing that stops the set is endurance rather than force.
Estimated against tested
A tested 1RM is the more exact number, and the 2020 systematic review by Grgic and colleagues found the test itself to be highly repeatable in both trained and untrained groups. What it costs is a session. Long warm-up, a spotter for bench and squat, a fresh nervous system, a day or two of extra recovery afterwards. Done monthly it interferes with training more than it informs it.
An estimate asks for none of that. Any hard working set you already logged becomes an input, so the number updates every session instead of every quarter. It will not tell you to the kilogram what you could lift today. It will tell you, across eight weeks, whether the line is going up, and for a training log that is the question worth answering.
What it does in a log
Raw sets are hard to compare. A week of 5 × 5 at 90 kg and a week of 3 × 8 at 80 kg are both bench pressing, and neither weight nor reps alone says which was stronger. Converted to estimates they become 101 kg and 99 kg, and the chart draws itself. That is why e1RM is the strength headline in a progress-tracking system. It normalises every rep scheme into one figure per lift.
It also sets personal records without a max attempt. If your best deadlift set was 140 kg × 5, your log can hold an estimated 1RM of about 158 kg, and update it the day you pull 140 × 6. No heavy single required.
Where it misleads
The formulas assume the set was taken close to failure. A comfortable 80 × 8 with four reps left is not the same input as a grinding one, and it reads low. In the other direction, past a dozen reps the formulas overshoot, sometimes by 10 percent or more, so feed them the heaviest set of the day rather than the longest.
Switching formulas mid-log is its own trap: a jump from Brzycki to Epley looks like progress on the chart when nothing happened. Choose one and leave it.
Two things the number does not do. It does not travel between exercises or variations, so paused bench and touch-and-go bench are separate records. And it is not a target. An e1RM of 100 kg is a description of your training, not permission to load 100 kg cold.
Strongbro computes an estimated 1RM per exercise from your best logged set using Brzycki, and keeps it as one of two automatic personal records alongside your best weight at each rep count. To try the arithmetic on a set of your own, the one-rep max calculator runs both formulas side by side. See also training volume and RPE, or the whole glossary.
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Frequently asked questions
What is the difference between a tested and an estimated 1RM?
A tested 1RM is a weight you actually lifted once. An estimated 1RM, often written e1RM, is calculated from a set of several reps using a formula. The test is more exact but costs a heavy, fatiguing session. The estimate is close enough to track direction, and it can be taken from any hard set you already logged.
Which 1RM formula is most accurate?
Brzycki and Epley agree within a kilogram or two for sets of 2 to 10 reps, and they return identical numbers at exactly 10 reps. Above 10 reps every formula drifts, because endurance starts to matter more than force. For tracking purposes, pick one formula and keep it; consistency matters more than the choice.
Should I test my true one-rep max?
Only if you compete, or your program calls for it. A true max needs a long warm-up, a spotter and a fresh day, and it leaves you tired for the rest of the week. An estimate from a set of 3 to 6 reps draws the same trend line without the risk or the recovery cost.
Why does my estimated 1RM change from session to session?
Because your sets do. Sleep, food, stress and the order of exercises all shift what you can do on a given day by a few percent, and the formula passes that straight through. Read the estimate as a weekly or monthly trend rather than a daily score, and treat one low day as noise.
Does the 1RM formula work for every exercise?
It works best on barbell and machine lifts with a stable range of motion, such as the squat, bench, deadlift and press. It is less reliable for bodyweight movements, for isolation work done at 15 or more reps, and for lifts where your technique gives out before your strength does.
What this is based on
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