Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How One Rep Max (1RM) Is Calculated
Your one-rep max (1RM) is the most weight you could lift for a single repetition. Testing it directly is risky, so most lifters estimate it from a lighter set taken to or near failure instead.
What This Calculator Measures
This gives a predicted 1RM from a single submaximal set, not a tested max. Treat it as a planning tool for setting training percentages, not a number to attempt directly without a proper warm-up.
The Formula
This calculator uses the Epley formula, one of the most commonly used 1RM estimates. In a comparison against tested maxes, Epley ran low for all three lifts, as most formulas did, though only slightly for the bench press².
1RM = weight lifted × (1 + reps ÷ 30)
How This Calculator Computes Your Result
Enter the weight you lifted and the number of reps you completed on that set. We apply the Epley formula directly and round to one decimal place.
Epley is the only formula this calculator uses. The other equations below are shown for comparison and do not change your result. Reps must be a whole number of 1 or more. Because Epley adds one thirtieth of the weight for every rep, a single rep returns a number about 3.3% above the weight you lifted, so if you lifted a weight once and could not have done a second rep, that weight is already your max.
How Epley Compares to Other Formulas
Epley isn’t the only widely used prediction equation. A comparison of several 1RM formulas against actual tested maxes in the bench press, squat, and deadlift found that only Mayhew’s and Wathan’s equations matched tested bench press maxes, only Wathan’s matched the squat, and all seven, Epley and Brzycki included, underestimated the deadlift². Errors also grow with longer sets: in a study of 70 adults, 5-rep maxes predicted 1RM better than 10- or 20-rep maxes⁸.
The table lists six of the seven equations LeSuer and colleagues tested² (the seventh is Lander’s), written in their usual forms. A later paper reprints their equation table³. The last two columns show what each one predicts from the same set of 5 reps.
Formula | 1RM equation | 225 lb × 5 | 100 kg × 5 |
Epley | weight × (1 + reps ÷ 30) | 262.5 lb | 116.7 kg |
Brzycki | weight × 36 ÷ (37 − reps) | 253.1 lb | 112.5 kg |
Lombardi | weight × reps^0.10 | 264.3 lb | 117.5 kg |
Mayhew | 100 × weight ÷ (52.2 + 41.9 × e^(−0.055 × reps)) | 267.8 lb | 119.0 kg |
O’Conner | weight × (1 + 0.025 × reps) | 253.1 lb | 112.5 kg |
Wathan | 100 × weight ÷ (48.8 + 53.8 × e^(−0.075 × reps)) | 262.3 lb | 116.6 kg |
At 5 reps the six estimates span about 15 lb, from 253.1 to 267.8 lb, or roughly 6%. Epley and Wathan land almost on top of each other, while Brzycki and O’Conner give the lowest numbers. The order changes with rep count: at 10 reps, Epley and Brzycki’s equation¹ give exactly the same answer (1.333 times the weight), while Lombardi and O’Conner come in about 6% lower.
No single curve fits every lift or every lifter. A 2024 meta-regression of 269 studies found that people completed more reps at the same percentage of 1RM on the leg press than on the bench press, and that rep counts varied between individuals at every load⁴. That helps explain why the same formula can read high for one exercise and low for another.
How to Use Your 1RM to Set Training Weights
Most programs prescribe loads as a percentage of 1RM. Multiply your estimate by the percentage you want: 80% of a 262.5 lb estimate is 210 lb, and 75% is about 197 lb. The Barbell Plate Calculator shows which plates to load for that total.
The American College of Sports Medicine’s 2026 position stand found that strength improved most with heavier loads, at or above 80% of 1RM, done for 2 to 3 sets at least twice a week. Muscle size grew more with at least 10 sets a week⁷. Its 2009 position stand suggests raising the load by 2 to 10% once you can do one or two reps more than your target at a given weight⁵.
Your strength also changes from day to day. The RPE Calculator uses how many reps you had left in reserve on today’s set to suggest a load for your next one, so you can adjust the percentage on stronger or weaker days.
1RM Percentage Chart by Reps
The share of your one-rep max that each formula expects you can lift for a given number of reps.
- Epley (this calculator)
- Brzycki
Show data table
| Reps | Epley (this calculator) (% of 1RM) | Brzycki (% of 1RM) |
|---|---|---|
| 1 | 96.8 | 100.0 |
| 2 | 93.8 | 97.2 |
| 3 | 90.9 | 94.4 |
| 4 | 88.2 | 91.7 |
| 5 | 85.7 | 88.9 |
| 6 | 83.3 | 86.1 |
| 7 | 81.1 | 83.3 |
| 8 | 78.9 | 80.6 |
| 9 | 76.9 | 77.8 |
| 10 | 75.0 | 75.0 |
| 11 | 73.2 | 72.2 |
| 12 | 71.4 | 69.4 |
A Note on Accuracy
This formula is most accurate for sets of about 10 reps or fewer. Higher-rep sets tend to overestimate true one-rep max. Use your estimated 1RM to plan training percentages, not as a target to attempt directly without proper warm-up and spotting. Prediction accuracy decreases as rep count rises, and results can vary more for smaller-muscle or technically demanding exercises.
Frequently Asked Questions
How accurate are one-rep max estimates?
Formulas like Epley and Brzycki give a fair estimate from sets of about 10 reps or fewer, but in one study they ran low for the squat and well low for the deadlift², and accuracy drops in longer sets⁸.
Which formula does this calculator use?
Only the Epley formula: 1RM = weight × (1 + reps ÷ 30). The other equations on this page are shown for comparison and do not affect your result.
Should I ever test my true one-rep max?
Occasional supervised testing can be useful. A review of 32 studies found 1RM tests reliable from one session to the next, with few adverse events reported, mostly muscle soreness⁶. For programming most training, an estimate from a submaximal set is usually enough.
Why does my estimated max seem off for some lifts?
Estimation formulas work best for compound lifts performed with consistent form. Technical or smaller-muscle exercises can produce less reliable estimates².
Sources
Strength Testing: Predicting a One-Rep Max from Reps-to-Fatigue, Brzycki, 1993
The Accuracy of Prediction Equations for Estimating 1-RM Performance in the Bench Press, Squat, and Deadlift, LeSuer et al., 1997
The Effects of Barbell Resistance Exercise on Information Processing Speed and Conflict-Related ERP in Older Adults: A Crossover Randomized Controlled Trial (Table 1, Prediction Equations From LeSuer et al.), Lin et al., Scientific Reports, 2021
Maximal Number of Repetitions at Percentages of the One Repetition Maximum: A Meta-Regression and Moderator Analysis of Sex, Age, Training Status, and Exercise, Nuzzo et al., Sports Medicine, 2024
American College of Sports Medicine Position Stand: Progression Models in Resistance Training for Healthy Adults, American College of Sports Medicine, 2009
Test-Retest Reliability of the One-Repetition Maximum (1RM) Strength Assessment: A Systematic Review, Grgic et al., Sports Medicine - Open, 2020
American College of Sports Medicine Position Stand: Resistance Training Prescription for Muscle Function, Hypertrophy, and Physical Performance in Healthy Adults, Currier et al., Medicine & Science in Sports & Exercise, 2026
Prediction of One Repetition Maximum Strength From Multiple Repetition Maximum Testing and Anthropometry, Reynolds, Gordon & Robergs, Journal of Strength and Conditioning Research, 2006