What this calculator does
It estimates the most you could lift once from a set you have already done. You enter the weight and the number of clean reps, and it returns the Epley estimate, the Brzycki estimate and their average, then a table of what 60 to 95 percent of that max is on the bar. For a working set at 80 kg for 6 the answer is about 95 kg, without ever loading 95.
It is for anyone whose program is written in percentages, anyone who wants one number to compare across months, and anyone who has been told to test a max and would rather not.
A worked example
Bench press, 80 kg (176 lb) for 6 clean reps, the last one slow.
| Formula | Arithmetic | Estimated 1RM |
|---|---|---|
| Epley | 80 × (1 + 6 ÷ 30) = 80 × 1.2 | 96 kg |
| Brzycki | 80 × 36 ÷ (37 − 6) = 80 × 36 ÷ 31 | 92.9 kg |
| Average | (96 + 92.9) ÷ 2 | 94.5 kg |
Now the percentages. A program that asks for 3 sets of 10 at 75 percent wants 0.75 × 94.5 = 70.9 kg, which is 70 kg once it meets the plates. A top set at 90 percent is 85 kg. And 85 percent comes out at 80.3 kg: the set you started from, which is the check that the estimate sits in the right place.
How the formulas work
Both formulas assume a fixed relationship between reps and the fraction of your max: each extra rep in a set costs a few percent of the load. Epley (1985) writes it as a straight line, 1RM = weight × (1 + reps ÷ 30), so every rep adds 3.3 percent. Brzycki (1993) writes it as a curve, 1RM = weight × 36 ÷ (37 − reps), which rises slowly at first and faster as the reps climb. The two meet at exactly 10 reps; below 10 Epley gives the higher number, which is why the calculator shows both and the average.
The percentage table runs the same idea backwards. The reps column is approximate and depends on the lift: most people get more reps at a given percentage on a leg press than on an overhead press.
| Of 1RM | Reps, roughly |
|---|---|
| 95% | 2 |
| 90% | 4 |
| 85% | 6 |
| 80% | 8 |
| 75% | 10 |
| 70% | 12 |
| 65% | 15 |
| 60% | 18 |
Why estimate instead of test
A true max is a skill and a day. It needs a taper, a warm-up that ends in near-maximal singles, a spotter, and a recovery that takes something from the rest of the week. On a weekly program it buys you one number and costs you a session. An estimate from a hard set of 3 to 8 reps costs nothing extra, because you were doing that set anyway, and it moves with you week to week.
The accuracy is good enough for programming. LeSuer et al. (1997, J Strength Cond Res 11(4):211–213) tested seven prediction equations against measured maxes in 67 untrained students; every one of them underestimated the deadlift (reference). The practical rule that follows: treat a deadlift estimate as a floor rather than a ceiling.
Limits of this tool
- It trusts your rep count. A set that ends with two grinders and a bounce gives a max you cannot lift. Count only the clean reps.
- Above 10 reps the two formulas separate and the estimate gets less reliable; the calculator warns and shows the number anyway. A set of 3 to 8 is a better input.
- It is lift-specific and person-specific. A deadlift estimate runs low (LeSuer 1997), and people differ: some get 12 reps at 70 percent, some get 9. Use the table as a starting point and your own log as the correction.
- An estimate is not a permission slip. Knowing your max is about 95 kg does not put 95 kg on the bar this week.
What BurnX does with this
The app never asks you to test a one rep max. Each week's working weights are set from what you actually lifted, and the session screen shows the day's weight in your unit. This calculator is for reading a percentage-based program, or for a number to put next to the date; the program itself does not need it.