Learn

1RM calculator: estimate your one-rep max from a set

By Setonomy · published October 25, 2026, updated October 27, 2026

Your 1RM is the weight you can lift exactly once in an exercise: your one-rep max. Instead of testing it with a max attempt, you can estimate it from a set of several reps^[1]. This calculator also uses RPE, meaning how many more reps you could have done at the end of the set^[2].

Calculate your 1RM

Enter the weight, how many reps you did and how hard the set was. If you went to failure, leave RPE at 10.

Estimated 1RM –

The formulas compared, with reps plus reps in reserve
Formula	1RM
Epley	–
Brzycki	–
Lander	–
Lombardi	–
Mayhew et al.	–
O’Connor et al.	–
Wathen	–
NSCA table	–

How the calculator works

It calculates the way Setonomy does: the reps in reserve are added to the reps you did, so two at RPE 8^[2]. That total goes into the Epley formula: weight × (1 + reps / 30)^[3]. RPE 9.5 counts as half a rep in reserve.

For example: 5 reps at 225 lb and RPE 8 make 5 + 2 = 7 reps. 225 × (1 + 7 / 30) gives a 1RM of 277.5 lb.

A single rep to failure isn't an estimate anymore: at 1 rep and RPE 10, your 1RM is the weight itself. At RPE 9.5, the formula already adds 5%.

Formulas compared

Epley is one of several well-known formulas. A 2023 study lists seven, Epley included, with their sources^[4]. The calculator shows their results below yours, as the formulas were published: the exception for a single rep to failure doesn't apply there, not even to Epley. There's also a table from an NSCA textbook that gives a percentage for 1 to 12 and for 15 reps to failure^[5]; for other numbers, the calculator shows no value there.

These formulas are made for sets to failure, so the calculator gives them the reps plus reps in reserve, just like Epley. A study on the bench press and leg press recommends using no more than 10 reps in linear equations^[1]. Beyond that, the formulas also spread further apart: at 225 lb and 10 reps to failure, the seven formulas range from 281.3 to 303.2 lb; at 12 reps, from 288.5 to 324.9 lb.

The formulas and their sources
Formula	Source
Epley	Boyd Epley Workout: Poundage chart (1985)
Brzycki	Journal of Physical Education, Recreation & Dance (1993)
Lander	National Strength and Conditioning Association Journal (1985)
Lombardi	Book “Beginning weight training” (1989)
Mayhew et al.	Journal of Applied Sport Science Research (1992)
O’Connor et al.	Book “Weight training today” (1989)
Wathen	Textbook “Essentials of strength training and conditioning” (1994)
NSCA table	NSCA textbook “Essentials of strength training and conditioning” (2016), as reproduced by Nuzzo et al. 2024^[5]

Percent of 1RM for training

The other way around, the table shows what percent of your 1RM fits a number of reps at a given RPE, using the same math. With a 1RM of 315 lb, 5 reps at RPE 8 come to about 255 lb.

Treat it as a guide, not an exact conversion: even the authors of a well-known RPE percentage chart write that it isn't an absolute tool, because people and days differ^[6].

Percent of 1RM by reps and RPE
Reps	RPE 10	RPE 9	RPE 8	RPE 7
1	100%	94%	91%	88%
2	94%	91%	88%	86%
3	91%	88%	86%	83%
4	88%	86%	83%	81%
5	86%	83%	81%	79%
6	83%	81%	79%	77%
7	81%	79%	77%	75%
8	79%	77%	75%	73%
9	77%	75%	73%	71%
10	75%	73%	71%	70%
11	73%	71%	70%	68%
12	71%	70%	68%	67%

How accurate is the estimate?

Even a tested 1RM isn't a fixed number: in a review of 32 studies, the median coefficient of variation between two tests was 4.2%, so results differ by a few percent^[7].

How many reps someone can do at a given percentage varies from person to person and also depends on the exercise: on the leg press, people get clearly more reps at the same percentage than on the bench press^[5]. A formula is right on average, but not for everyone.

People tend to underestimate their reps in reserve by almost one rep, and with more than 12 reps to failure, their estimates are further off^[8]. RPE is most reliable close to failure^[2]. So the estimate is most accurate from a hard set with few reps.

1RM in Setonomy

Setonomy estimates your 1RM automatically from your hard sets, with the same math. Checked-off sets with fewer than 10 reps at RPE 8.5 or higher, which with the buttons means “Hard” or “Max,” count toward your records. Next to them is “now,” your current 1RM from sets of up to 12 reps at RPE 8.5 or higher: recent workouts count more, and it can go down too. For each exercise, only the first set at RPE 8.5 or higher in a workout counts; after it, the estimate would come out too low. From your training, both only come from sets with a recorded RPE; to record it, turn on “Use target RPE” in Settings.

If you know your max, enter it with “Log 1RM” and a date; it counts like one rep at RPE 10. The records list is free. More in help on progress and records and in the article RPE and RIR.

Records in Setonomy: “Exercises with 1RM” at the top, 6 of 12 exercises in the list, and “Log 1RM,” then each exercise's record and date with “now,” for example Bench Press 237 lb with “now 228.4 lb · 96 %” and Dips +81.6 lb with “now +86 lb · 102 %” and “Time for a test?” — Progress → Records: each exercise's record, with “now” below it and its share of the record as a percentage, including your body weight for bodyweight exercises. When “now” is above the record, “Time for a test?” appears below it. The list is free; you only need Premium to pin records to the dashboard.

Frequently asked questions

What is a 1RM?

The weight you can lift exactly once in an exercise. The calculator estimates it from a set of several reps^[1].

Which formula is best?

None is right for everyone. In one study, equations based on 5 reps to failure predicted the 1RM most accurately, more so than those based on 10 or 20^[1]. The calculator shows Setonomy's math as the result and the others for comparison.

What should I enter as RPE?

If you went to failure, it's RPE 10. Otherwise, estimate how many more reps you could have done: RPE 8 means two^[2]. More in the article RPE and RIR.

Why is there no result above 12 reps?

The more reps, the less accurate it gets: linear formulas shouldn't use more than 10^[1], and above 12 reps, estimates of the reserve are further off too^[8]. Setonomy uses sets of up to 12 reps for your current 1RM.

Can I calculate in kilograms?

Yes, choose “kg” next to the weight. The math is the same; the result is then in kilograms, rounded to one decimal place.