1RM Calculator
Estimate your one-rep max using the Epley and Brzycki formulas, the two most widely cited models in strength training.
Enter the weight you lifted and the number of clean reps. Both standard formulas are shown.
How is this calculated?
Epley (1985): 1RM = weight × (1 + reps / 30). Brzycki (1993): 1RM = weight × 36 / (37 - reps). Accuracy is best for 1 to 10 reps; both formulas drift above 10.
About this tool
A 1RM (one-rep max) calculator estimates the heaviest weight you could lift for a single clean repetition based on a sub-maximal set you actually performed. It is the standard way to set training percentages without grinding through risky max attempts every week.
The Epley and Brzycki equations were both derived in the 1980s and 1990s from regression analysis of competitive lifter data. Coaches like Mark Rippetoe, Jim Wendler, and Greg Nuckols still cite them in modern programs because their accuracy holds up well in the 1 to 8 rep window, which covers nearly every working set a serious strength athlete performs. Averaging the two outputs cancels out most of each formula's individual drift.
How it works
The calculator runs your input through both classic rep-max prediction equations and reports the average. Both were derived empirically from regression on competitive lifter data.
Epley (1985): 1RM = w x (1 + r / 30)
Brzycki (1993): 1RM = w / (1.0278 - 0.0278 x r)
(equivalent form: w x 36 / (37 - r))
- w = weight lifted on the working set (kg or lb).
- r = number of clean reps performed, taken to within 1 or 2 reps of failure.
- 30 and 0.0278 = regression constants the authors fit to powerlifter and bodybuilder data sets.
- Valid range = 1 to 10 reps. Above 10 reps the linear model breaks because endurance, not max strength, drives the load.
Worked example
A lifter benches 100 kg for 5 clean reps, leaving 1 rep in reserve. What is the estimated 1RM?
- Inputs: w = 100 kg, r = 5.
- Epley: 100 x (1 + 5 / 30) = 100 x 1.1667 = 116.7 kg.
- Brzycki: 100 x 36 / (37 - 5) = 3600 / 32 = 112.5 kg.
- Average: (116.7 + 112.5) / 2 = 114.6 kg.
- Plan training percentages off the average: 80 percent for sets of 8 = 91.7 kg, 90 percent for triples = 103.1 kg.
Percent of 1RM reference table
This is the standard intensity-to-reps mapping used in 5x5, Texas Method, Wendler 5/3/1, and most periodised templates. Numbers are averages across the strength-training literature.
| Percent of 1RM | Approx reps to failure | Typical use |
|---|---|---|
| 100 percent | 1 | Competition or testing attempt |
| 95 percent | 2 | Peak strength singles or doubles |
| 90 percent | 4 | Heavy triples, top sets in 5/3/1 |
| 85 percent | 6 | Strength sets of 5 |
| 80 percent | 8 | Hypertrophy-strength blend |
| 75 percent | 10 | Volume sets, accessory work |
| 70 percent | 12 | Hypertrophy, technique practice |
| 65 percent | 15 | Warm-up, endurance, deload |
Common mistakes and limitations
- Counting grindy reps. Both formulas assume crisp reps with 1 to 2 in reserve. If your last rep took 8 seconds and shook, the calculator will overestimate.
- Going above 10 reps. Endurance dominates above 10, so a 20-rep set predicts a 1RM that you cannot actually lift.
- Mixing lifts. A 1RM estimate is exercise-specific. Your bench 1RM does not predict your overhead press, and a paused squat 1RM will be lower than a touch-and-go squat.
- Testing at the wrong time. Fatigue, dehydration, and sleep debt drop measured strength 5 to 15 percent. Test on a fresh day after a deload.
- Treating the number as a goal. Use the estimate to set training loads, not as a max to attempt the next session.
- Ignoring bar weight in raw entries. Always include the empty bar (20 kg for an Olympic barbell, 15 kg for a women's bar, 7 to 9 kg for trap bars and EZ-curl bars). Lifters who enter "two 20 kg plates per side" without the bar systematically undercount by 20 kg and produce a 1RM that is well below their actual ceiling.
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Frequently asked questions
Which formula is more accurate, Epley or Brzycki?
Both formulas agree to within about 2 percent at 1 to 5 reps. Brzycki tends to under-estimate the true 1RM at 8 reps and above, while Epley tends to over-estimate at the same point. Most coaches average the two, or use Epley for compound lifts (squat, deadlift) and Brzycki for upper-body presses where high-rep performance falls off faster.
How many reps should I use to estimate my 1RM?
Use a set taken to within 1 or 2 reps of failure in the 3 to 8 rep range. Below 3 reps you might as well attempt an actual 1RM; above 10 reps the formulas drift because muscular endurance starts to drive performance more than maximum strength. A 5RM is the sweet spot for most lifters.
Is the calculated 1RM safe to attempt in the gym?
Treat the estimate as a ceiling, not a target. Work up to it gradually, use safety bars or spotters, and only attempt a true 1RM when you are fresh, warmed up, and technically proficient. Most coaches recommend testing 1RM no more than every 8 to 12 weeks because it is fatiguing and carries injury risk.
Why does my training log use a percentage of 1RM?
Percentage-based programming (5x5 at 80 percent, 3x3 at 90 percent, etc.) lets you scale intensity to your current strength rather than to a fixed weight. Most strength templates assume the standard percent-to-reps table: 95 percent equals roughly 2 reps, 90 percent equals 4, 85 percent equals 6, 80 percent equals 8, 75 percent equals 10.
Does the calculator work for deadlift and squat the same as bench press?
The formulas were originally calibrated on bench press but apply reasonably well to the squat and deadlift in the 1 to 6 rep range. Deadlift performance falls off faster across reps than bench, so at 8+ reps the calculator tends to overstate deadlift 1RM by 5 to 8 percent. For deadlift estimates above 5 reps, lean toward the lower of the two formula outputs (usually Brzycki).
Sources
- Epley, Boyd (1985) Poundage Chart, Boyd Epley Workout, Lincoln NE - the original Epley equation.
- Brzycki, Matt (1993) Strength testing: Predicting a one-rep max from reps-to-fatigue, JOPERD 64(1): 88 to 90.
- ACSM (2021) Guidelines for Exercise Testing and Prescription, 11th edition, Chapter on resistance training and load prescription.
- Mayhew et al. (1992) Muscular endurance repetitions to predict bench press strength, J Appl Sport Sci Res 6(4): 200 to 206.