What Is a One-Rep Max (1RM)? Formula and Example | 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. Most lifters never test it directly; they estimate it from a submaximal set with 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 number the rest of your log is measured against. Program percentages are written as fractions of it, personal records are ranked by it, and "am I stronger than in March" is answered by it. Here is what it means, how it is calculated, and where it misleads.
How it's calculated
There are two routes to a 1RM. The direct route is to test it: warm up, add weight in small jumps, and find the heaviest single you can complete with good form. The indirect route is to estimate it from a set of several reps using 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 limiting factor becomes endurance rather than force.
Estimated vs 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 across trained and untrained groups. What the test costs is a session: a long warm-up, a spotter for bench and squat, a fresh nervous system, and a day or two of extra recovery afterwards. Done monthly it interferes with training more than it informs it.
An estimated 1RM 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, over eight weeks, whether the line is going up. For a training log that is the question that matters.
Why it matters for your 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, but neither weight nor reps alone says which was stronger. Converted to an estimate, they become 101 kg and 99 kg, and the chart draws itself. That is why the 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, with no heavy single required.
Common mistakes
- Estimating from a set that stopped early. 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 will read low.
- Estimating from 15-rep sets. Past a dozen reps the formulas overshoot, sometimes by 10 percent or more. Use the heaviest set of the day, not the longest.
- Switching formulas mid-log. A jump from Brzycki to Epley looks like progress on the chart. Choose one and leave it.
- Comparing across exercises. A 1RM is per lift and per variation. Paused bench and touch-and-go bench are different records.
- Treating the estimate as 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 the Brzycki formula, and keeps it as one of two automatic personal records alongside your best weight at each rep count. To try the numbers on a set of your own, the one-rep max calculator runs both formulas side by side. Related terms: training volume, RPE, and the full 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 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 give identical results at exactly 10 reps. Above 10 reps every formula drifts, because endurance starts to matter more than strength. For tracking, 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 needs it. A true max requires a long warm-up, a spotter and a fresh day, and it leaves you tired for the rest of the week. For most people an estimate from a set of 3 to 6 reps gives 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 through. Read the estimate as a weekly or monthly trend rather than a daily score, and treat a single 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 squat, bench, deadlift and press. It is less reliable for bodyweight movements, for isolation exercises done at 15 or more reps, and for lifts where technique limits you before strength does.
What this is based on
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