One-Rep Max Calculator
Estimate one-rep max from sub-maximal sets using Epley + Brzycki + Lander + Lombardi + O'Conner formulas. Includes a % of 1RM table with ACSM training zones.
One-Rep Max Calculator
| Reps | % of 1RM | Weight | Best for |
|---|---|---|---|
| Enter weight × reps (1-12) to estimate 1RM | |||
Every row uses the same five-formula average as the headline, run backwards: the weight that average puts at each rep count. The row for the reps you entered returns the weight you entered.
How to use the 1RM Calculator
Pick a recent sub-max set
Use a set you finished with good form, between 1 and 12 reps. In a study of 103 college women's bench press, the equations were more accurate on sets of fewer than 10 reps (Mayhew et al., 2008). On this tool's five formulas the estimates also agree more closely at lower reps: within about 7% of each other up to 8 reps, spreading to about 16% at 12. Bench, squat, deadlift and overhead press all work.
Enter weight + reps performed
Enter the weight in kg or lb; the result comes back in the same unit. Enter the reps you actually completed with good form, not the number you think you could have done. Only whole reps count, and a single rep returns the weight you lifted.
Read estimated 1RM + per-formula breakdown
The headline is the average of five published formulas. The breakdown shows each one, and the spread line tells you how far apart they are for your rep count. A wide spread means the estimate is less certain.
Read the rep table
Each row is a rep count from 1 to 12, the share of your estimated 1RM that the same five-formula average puts at that count, and the weight. The row for the reps you entered returns the weight you entered. The last column gives the matching zone from the American College of Sports Medicine: heavy 1-6 RM loads for strength emphasis, 6-12 RM for muscle size.
1RM — the foundation of structured strength training
A one-rep max (1RM) is the heaviest weight you can lift once with good form. Many strength programmes set loads as a percentage of it, so a reasonable estimate lets you plan training without testing a true maximum. This calculator estimates it from a lighter set you have already done, using five published formulas, and shows how far they disagree.
The five formulas
Epley: 1RM = w × (1 + r/30). Who first wrote this form is disputed: Lacio et al., 2010 credit Boyd Epley's 1985 poundage chart, while Mayhew et al., 2008 list the same equation under Welday (Scholastic Coach, 1988). Brzycki (Brzycki, 1993, in the Journal of Physical Education, Recreation & Dance): commonly written 1RM = w × 36 / (37 − r), the form this tool uses; Mayhew and colleagues print it as w / (1.0278 − 0.0278 × r), which differs by less than 0.1% of the weight up to 12 reps. Lander (1984, often cited as 1985, in the National Strength & Conditioning Association Journal): 1RM = 100 × w / (101.3 − 2.67123 × r). Lombardi (Beginning Weight Training, 1989): 1RM = w × r^0.10. O'Conner (O'Conner, Simmons and O'Shea, Weight Training Today, 1989; the name is also printed O'Connor): 1RM = w × (1 + 0.025 × r). The book references for Lombardi and O'Conner are as Mayhew and colleagues list them. Three of them, Epley, Lander and O'Conner, would put a single rep above the weight lifted, so for a 1-rep entry this tool returns the weight itself: a single is already a maximum for that day.
How much they disagree
The formulas agree closely at low reps and drift apart as reps rise. Running all five on the same set, the spread between the highest and lowest estimate is about 6% of the weight at 3 reps, 5% at 5 reps and 7% at 8 reps, then about 16% at 12 reps. That is why the tool asks for 12 reps or fewer. Agreement between formulas is not the same as accuracy, though. Mayhew and colleagues compared 14 published equations and wrote that most "gave no evidence of the population used to develop the equations" (Mayhew et al., 2008). In their study of 103 college women's bench press, each of the five formulas used here had an average error within 4% of the tested maximum on sets of fewer than 10 reps, but individual errors were around 9 to 11% (one standard deviation). Two exponential equations in that study, credited to Mayhew and to Wathen, are not used here; the Wathen equation, the authors note, was "calculated from chart provided". A maximum you have actually lifted always beats an estimate.
Using the percentage table
The rep table runs the same five-formula average backwards: on that average, 8 reps sits at about 81% of the estimated 1RM and 12 reps at about 73%. The zones come from the American College of Sports Medicine's 2009 position stand on resistance training (ACSM position stand, 2009). It recommends that beginners train with loads they can lift 8 to 12 times. For strength, intermediate and advanced lifters should use 1 to 12 RM in a periodised plan with an emphasis on heavy 1 to 6 RM loads and 3 to 5 minutes' rest. For muscle size the emphasis is 6 to 12 RM with 1 to 2 minutes' rest, and for muscular endurance 40 to 60% of 1RM for more than 15 reps. When you can do one or two reps more than planned, it suggests adding 2 to 10% to the load.
Five formulas, how far they drift, and ACSM's training zones
A one-rep max is the heaviest weight you can lift once with good form. Many programmes set training loads as a percentage of it.
Epley's formula is 1RM = weight × (1 + reps/30); Mayhew et al. (2008) credit the same form to Welday (1988).
Brzycki's formula, published in 1993, is commonly written 1RM = weight × 36 / (37 − reps).
Lander's formula appeared in the National Strength & Conditioning Association Journal in 1984.
For a single rep this tool returns the weight itself, because a single is already a maximum for that day.
Across the five formulas, the estimates stay within about 7% of each other from 2 to 8 reps.
At 12 reps they spread to about 16%, which is why this tool stops at 12.
ACSM recommends beginners train with loads they can lift 8 to 12 times.
For strength, ACSM emphasises heavy 1-6 RM loads with 3 to 5 minutes' rest between sets.
For muscular endurance, ACSM recommends 40-60% of 1RM for more than 15 reps with short rests.
Frequently Asked Questions
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No study has shown one to be best for everyone, and most were published without saying who they were developed on (Mayhew et al., 2008). In that study of 103 college women's bench press, each of the five formulas used here had an average error within 4% of the tested maximum when sets were under 10 reps, but individual errors were around 9 to 11%. What this page can show is how much the formulas agree. Across the five, the spread is about 6% of the weight lifted at 3 reps and 7% at 8, growing to about 16% at 12. This tool averages all five and shows the spread so you can judge how far to trust the number.
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You do not need to for most training. An estimate from a recent set is enough to set percentages, and it avoids lifting a true maximum. If you compete or want a tested number, work up through progressively heavier warm-up sets, use a spotter or safety bars on bench and squat, and stop when your form breaks down. A coach can plan the attempt with you.
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Whenever your working sets change. The American College of Sports Medicine suggests adding 2 to 10% to a load once you can do one or two reps more than planned. When that happens, your old estimate is too low: re-enter your latest set and let the calculator give you a new number. If you are missing reps you used to make, the estimate is too high, and a lighter recent set will correct it.
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No. Estimate each lift separately. A squat, a bench press and a deadlift use different muscles and leverage, so one lift's maximum tells you little about another's. Enter a recent set for each lift you want to plan around.
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They may not, and this page no longer claims they do. What is clear is that a beginner's strength changes quickly and technique is still settling, so any estimate goes out of date faster. The American College of Sports Medicine recommends that beginners train with loads they can lift 8 to 12 times, which is well below a maximum, so an exact 1RM matters less early on.
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The American College of Sports Medicine's 2009 position stand recommends loads of 1 to 12 RM in a periodised plan, with an emphasis on 6 to 12 RM and 1 to 2 minutes' rest between sets, and higher-volume, multiple-set programmes. In this tool's table, 6 to 12 reps corresponds to roughly 73% to 85% of your estimated 1RM.
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It can. Power training, which matters in many sports, uses percentages of 1RM: the American College of Sports Medicine recommends 30% to 60% of 1RM for upper-body exercises and 0% to 60% for lower-body exercises, lifted fast, with 3 to 5 minutes' rest and three to five sets. Muscular endurance work uses 40% to 60% of 1RM for more than 15 reps. An estimate lets you set those loads without testing a maximum.
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It varies too much between people to give a reliable figure, so this page does not. The practical rule is the one the American College of Sports Medicine gives for progressing: when you can do one or two reps more than planned at a load, add 2% to 10%. Re-estimate your 1RM from a recent set as your working weights go up.
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No. The calculation runs in your browser and sends nothing: the weight and reps you enter are not transmitted or saved. The page itself, like any web page, makes other requests as it loads, such as for analytics and ads where you have allowed them.
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Method & sources
How it computes
Averages Epley (w × (1 + r/30); Mayhew et al. 2008 list this form under Welday 1988), Brzycki (w × 36/(37 − r)), Lander (100w/(101.3 − 2.67123r)), Lombardi (w × r^0.10) and O'Conner (w × (1 + 0.025r)) over whole reps, 1-12; a single rep returns the weight lifted. The page reports the spread between formulas. The rep table runs the same average backwards, so the row for the entered reps returns the entered weight; its zones follow the ACSM 2009 position stand.
What this tool implements
- Fractional reps were accepted and a 1-rep entry returned more than the weight lifted under three formulas. Reps are now rounded and a single returns the weight. The table's reps were typed and disagreed with every formula at 65% and 50%; they are now computed.
- Spread measured on the five formulas: about 6% at 3 reps, 5% at 5, 7% at 8, 16% at 12. This replaces an unsourced '3-8 reps most accurate / ±5%' claim and 'untrained overestimate 10-20%'.
- Removed: named ASEAN gyms and clubs that could not be verified, bodyweight-ratio standards, first-year gain percentages and an unsourced pull-quote. ACSM 2009 is quoted for 8-12 RM (novice), 1-6 RM emphasis (strength), 6-12 RM (hypertrophy), 30-60% / 0-60% (power), 40-60% for >15 reps (endurance) and 2-10% load progression.
- Removed "each formula was fitted to particular lifters and lifts": Mayhew et al. 2008 found most published equations "gave no evidence of the population used to develop the equations". Accuracy is now quoted from that study (bench press, 103 college women), not inferred from the formulas agreeing.
Sources
- 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
- Lander J. Maximum based on reps. Natl Strength Cond Assoc J 1984;6:60. https://doi.org/10.1519/0744-0049(1984)006<0060:MBOR>2.3.CO;2
- American College of Sports Medicine. Position stand: progression models in resistance training for healthy adults. Med Sci Sports Exerc 2009;41(3):687-708. https://doi.org/10.1249/MSS.0b013e3181915670
- 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):1570-7 — 14 equations compared; lists the w × (1 + 0.0333r) form under Welday (1988) and the Wathen equation as "calculated from chart provided". https://doi.org/10.1519/JSC.0b013e31817b02ad
- Lacio ML, Damasceno VO, Vianna JM, et al. Precisão das equações preditivas de 1-RM em praticantes não competitivos de treino de força. Motricidade 2010;6(3):31-7 — credits the same form to Epley's poundage chart. https://www.redalyc.org/pdf/2730/273019708005.pdf
- Welday J. Should you check for strength with periodic max lifts? Scholastic Coach 1988;57(9):49-68 (as listed by Mayhew et al. 2008).
- Lombardi VP. Beginning Weight Training. Dubuque, IA: W.C. Brown; 1989 (as listed by Mayhew et al. 2008).
- O'Conner B, Simmons J, O'Shea P. Weight Training Today. St Paul, MN: West Publishing; 1989 (as listed by Mayhew et al. 2008, which also prints the name O'Connor).
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