# One rep max calculator

> Estimate your one rep max from any set of 1–20 reps and its RIR. Epley plus six other formulas, the likely range and where the estimate gets rough.

Updated 2026-09-27. Canonical: https://povver.ai/tools/one-rep-max-calculator

## Worked example

Example: 100 kg for 5 reps with 2 in reserve.

- Estimated 1RM (Epley on 7 reps to failure): 123.3 kg
- Likely range 114.2–132.5 kg
- From reps alone: 116.7 kg
- Reliability: moderate

### Same set, other formulas (7 reps to failure)

| Formula | 1RM (kg) |
|---|---|
| Epley (Povver) | 123.3 |
| Brzycki | 120 |
| Lander | 121.1 |
| Lombardi | 121.5 |
| Mayhew | 123.9 |
| O’Conner | 117.5 |
| Wathen | 124 |

Spread: 6.5 kg, O’Conner lowest, Wathen highest.

### Rep maxes at 123.3 kg (Epley, loads rounded)

| Reps | % of 1RM | Load (kg) |
|---|---|---|
| 1 | 100.0% | 122.5 |
| 2 | 93.8% | 115 |
| 3 | 90.9% | 112.5 |
| 4 | 88.2% | 110 |
| 5 | 85.7% | 105 |
| 6 | 83.3% | 102.5 |
| 7 | 81.1% | 100 |
| 8 | 78.9% | 97.5 |
| 9 | 76.9% | 95 |
| 10 | 75.0% | 92.5 |
| 11 | 73.2% | 90 |
| 12 | 71.4% | 87.5 |

## The seven equations

w is the weight lifted, r is reps to failure (reps plus reps in reserve, RIR above 3 counted as 3). A single to failure returns the weight itself.

| Formula | Year | 1RM = |
|---|---|---|
| Epley | 1985 | w × (1 + r/30) |
| Brzycki | 1993 | w / (1.0278 − 0.0278r) |
| Lander | 1985 | w / (1.013 − 0.0267123r) |
| Lombardi | 1989 | w × r^0.10 |
| Mayhew | 1992 | w / (0.522 + 0.419e^(−0.055r)) |
| O’Conner | 1989 | w × (1 + 0.025r) |
| Wathen | 1994 | w / (0.488 + 0.538e^(−0.075r)) |

## How it works

Reps plus reps in reserve gives the reps you could have done. That number goes through Epley:

- 1RM = weight × (1 + (reps + RIR) / 30)
- RIR above 3 counts as 3, since lifters judge it poorly far from failure (Halperin 2022)
- a single with nothing left is its own 1RM

So 100 kg for 5 with 2 in reserve is 7 reps to failure: 100 × (1 + 7/30) = 123.3 kg. The six other formulas run on the same 7 reps. At 1 rep to failure, all seven return the weight lifted.

Lombardi's exponent is 0.10 in Reynolds 2006 and 0.13 in Mayhew 2008. We use 0.10.

The rep-max table runs Epley backwards from your estimate. Loads round to the nearest 1.25 kg up to 40 kg, 2.5 kg above, or 5 lb.

## How far to trust it

Every formula was fitted to sets taken to failure, and each gets less accurate as the reps climb.

- Fewer than 10 reps gave better estimates (Mayhew 2008, 103 women, bench press).
- Reynolds and colleagues advise using no more than 10 reps in a linear equation (Reynolds 2006).
- In that study, a 5 kg error in a 5RM grew to 19.7 kg in the predicted leg press 1RM. On the chest press it was 6.3 kg.
- In 67 untrained students, every equation under-predicted the deadlift (LeSuer 1997).

The reliability grade is ours, set by reps to failure: 1 to 6 high, 7 to 12 moderate, above 12 rough.

No study has tested adding reps in reserve to reps for a 1RM estimate. We do it because Povver does, and because lifters judge RIR near failure to within about one rep (Halperin 2022). Far from failure, the answer is a guess. Read the range.

The range is reps to failure, plus or minus a quarter of itself, run through Epley. Enter RIR and it widens by one more rep. The quarter is how much lifters differ: at a given share of 1RM, the reps people manage vary by about a quarter of the average (Nuzzo 2024). The extra rep is the usual miss in judging RIR (Halperin 2022).

Which formula to trust at which rep count, tested against real maxes: [1RM formulas compared](/blog/1rm-formula).

## In the Povver app

Povver estimates your 1RM on every lift each week from your best set: Epley on reps plus reps in reserve.

## Sources

1. Reynolds JM, Gordon TJ, Robergs RA. Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. J Strength Cond Res. 2006;20(3):584–592. https://doi.org/10.1519/R-15304.1
2. 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. J Strength Cond Res. 1997;11(4):211–213. https://doi.org/10.1519/00124278-199711000-00001
3. 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):1570–1577. https://doi.org/10.1519/JSC.0b013e31817b02ad
4. Epley B. Poundage chart. Boyd Epley Workout. Lincoln, NE; 1985.
5. Brzycki M. Strength testing—predicting a one-rep max from reps-to-fatigue. JOPERD. 1993;64(1):88–90. https://doi.org/10.1080/07303084.1993.10606684
6. Nuzzo JL, Pinto MD, Nosaka K, Steele J. Maximal number of repetitions at percentages of the one repetition maximum: a meta-regression and moderator analysis of sex, age, training status, and exercise. Sports Med. 2024;54(2):303–321. https://doi.org/10.1007/s40279-023-01937-7
7. Halperin I, Malleron T, Har-Nir I, et al. Accuracy in predicting repetitions to task failure in resistance exercise: a scoping review and exploratory meta-analysis. Sports Med. 2022;52:377–390. https://doi.org/10.1007/s40279-021-01559-x