One-rep max calculator
Enter the weight and reps of a hard set to estimate your one-rep max (1RM), the heaviest single you could lift today. It uses the same formula as the Muscla app.
Filled in with example values. Replace them with yours.
Estimated 1RM
Brzycki 112.5 · Lombardi 117.5
Epley: 100 × (1 + 5 ÷ 30) = 116.7 kg
Load 117.5 kg on the bar →| Reps | Weight | % of 1RM |
|---|---|---|
| 1 | 117.5 kg | 100 % |
| 2 | 110 kg | 94 % |
| 3 | 105 kg | 91 % |
| 4 | 102.5 kg | 88 % |
| 5 | 100 kg | 86 % |
| 6 | 97.5 kg | 83 % |
| 7 | 95 kg | 81 % |
| 8 | 92.5 kg | 79 % |
| 9 | 90 kg | 77 % |
| 10 | 87.5 kg | 75 % |
| 11 | 85 kg | 73 % |
| 12 | 82.5 kg | 71 % |
How the estimate works
The calculator uses the Epley formula, the same one Muscla uses in the app:
1RM = weight × (1 + reps ÷ 30)
Each rep adds about 3.3 % to the weight you lifted. Five reps with 100 kg give 100 × (1 + 5 ÷ 30) = 116.7 kg. A single rep is not estimated: if you lifted it once, that is your 1RM.
Most sets do not go to failure, and they should not have to. That is why the calculator asks how many more reps you could have done. Those reps in reserve count as reps done: five reps with two left in the tank read like seven reps to failure. This follows the reps-in-reserve scale from strength research (Zourdos 2016, Helms 2016). Muscla asks the same question after your main lifts and uses the answer to set your next workout.
Above 12 reps the calculator gives no number on purpose. At that point a set measures how long you can keep going more than how strong you are, and every formula starts to guess.
Epley, Brzycki or Lombardi?
There are dozens of 1RM formulas, and three are used most. They agree closely between 2 and 6 reps and drift apart above 10:
- Epley (1985) adds a fixed share per rep. It sits in the middle of the three at typical rep counts, which makes it a good default.
- Brzycki (1993) gives a slightly lower number for the same set and rises steeply at high reps.
- Lombardi (1989) uses a power curve. It reads a little higher at low reps and flatter at high reps.
Under the result you see the Brzycki and Lombardi numbers for your set. When all three are close, the estimate is solid. When they spread apart, your set had too many reps to say much about a single.
How accurate is it?
An estimate is most reliable from a hard set of 2 to 6 reps with clean technique, close to failure. In a study of seven equations against tested maxima, results were closest for the bench press and squat and least accurate for the deadlift (LeSuer 1997).
Expect a few percent either way. Your training history, how quickly you tire and the exercise itself all move the number. Machines and cables often allow more reps at the same share of your max than free weights. Treat the result as a starting point: once you log your sets, they correct it.
1RM percentage chart: training weights by reps
The table under the calculator shows the weight for each number of reps, if you take the set to failure. Most training stops one to three reps short of failure, so pick the row a few reps higher than the reps you plan. For sets of 8 with 2 reps in reserve, start near the 10-rep weight.
All weights are rounded to what you can load on a barbell: steps of 2.5 kg (a 1.25 kg plate on each side) or 5 lb. If your gym has smaller plates, you can go between the rows.
As a rough guide, strength is built mostly with heavy sets of 1 to 5 reps, around 85 % of your 1RM and above. Muscle grows across a wide range of loads, from about 6 to 30 reps, as long as the sets end close to failure (Schoenfeld 2017). Most lifters do both: heavy work on the main lifts, moderate weights for the rest.
Testing a true 1RM safely
If you want to test a real max, warm up in steps of roughly 50, 70, 85 and 92 % of what you expect, with a few reps early and a single near the top. Rest three to five minutes before each heavy attempt. Use safety pins or a spotter on the squat and the bench press, and stop when the bar slows down sharply or your technique changes. A clean single you could repeat tells you more than a grinder you barely survive.
Your 1RM in Muscla
Muscla estimates your 1RM from every set you log, draws your strength curve for each exercise and tells you when you set a new best. The weights in your plan come from the same estimate and adjust after every workout, based on how hard each exercise felt.
Coming to the App Store. Free to start.
Questions
What is a one-rep max?
Your one-rep max (1RM) is the heaviest weight you can lift for one clean repetition of an exercise. It is the usual yardstick for strength, and training programs often give their weights as a percentage of it.
How many reps give the most accurate estimate?
A hard set of 2 to 6 reps with clean technique. The fewer reps between your set and a single, the less the formula has to guess. Sets above 10 reps depend more on endurance, so the estimate spreads out.
Why does the calculator stop at 12 reps?
Above 12 reps the formulas drift apart quickly and the result says more about how long you can keep going than about your maximal strength. Muscla does the same in the app: a set above 12 reps does not change your 1RM.
Should I train with my estimated or my tested 1RM?
Either works if it is honest. An estimate from a recent hard set is often closer to your strength on a normal day than a max you tested on your best day months ago. Muscla updates the estimate after every workout, so your plan follows your real strength.
Is my 1RM the same for every exercise?
No. Each exercise has its own 1RM, and even the same movement differs between a barbell, dumbbells and a machine. Estimate each lift from its own sets.
How often should I test a real 1RM?
You do not have to. If you like to test, the end of a training block every few months is plenty. In between, estimates from your regular sets track your progress with far less fatigue.
Sources
- Epley B. Poundage Chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises; 1985.
- Brzycki M. Strength testing: predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation and Dance. 1993;64(1):88-90.
- Lombardi VP. Beginning Weight Training: The Safe and Effective Way. Dubuque, IA: W. C. Brown; 1989.
- LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research. 1997;11(4):211-213.
- Zourdos MC, Klemp A, Dolan C, et al. Novel resistance training-specific rating of perceived exertion scale measuring repetitions in reserve. Journal of Strength and Conditioning Research. 2016;30(1):267-275.
- Helms ER, Cronin J, Storey A, Zourdos MC. Application of the repetitions in reserve-based rating of perceived exertion scale for resistance training. Strength and Conditioning Journal. 2016;38(4):42-49.
- Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW. Strength and hypertrophy adaptations between low- vs. high-load resistance training: a systematic review and meta-analysis. Journal of Strength and Conditioning Research. 2017;31(12):3508-3523.