One Rep Max Calculator: Epley, Brzycki, Lander Formulas, and How to Estimate Your 1RM

Your one-rep max (1RM) — the heaviest weight you can lift for exactly one repetition with proper form — is the gold standard of strength assessment and the reference value behind every percentage-based training programme ("5×3 at 85% 1RM"). It's also dangerous to test directly, particularly on squat, bench, and deadlift, where maximal attempts produce most lifting injuries.

The good news: you don't need to actually test your 1RM. Six well-validated prediction equations — Epley, Brzycki, Lander, Lombardi, O'Conner, and Mayhew — can estimate your 1RM from a submaximal set with about 5% accuracy when rep counts are kept low. This guide covers all six formulas, when to use each, how to adjust for RPE/RIR, and how to translate your estimated 1RM into precise training loads for hypertrophy, strength, and peaking.

What Is a One Rep Max (1RM)?

A one-rep maximum is the heaviest weight you can lift through a complete range of motion for exactly one repetition before form breaks down. It is exercise-specific (your squat 1RM is different from your bench press 1RM), changes over time as you train or detrain, and is the reference number behind nearly every structured strength programme ever written.

Why it matters:

• Training prescription. Percentage-based programming uses 1RM as the anchor: "65% of 1RM for 4×8" produces a different stimulus than "85% for 5×3." Without a reasonable 1RM estimate, you can't use most evidence-based templates.
• Strength comparison. Tools like the Wilks score normalise 1RM across body weight to compare strength fairly. See our Wilks score explained guide.
• Progress tracking. 1RM is a single-number summary of strength at a point in time. Tracking it across a training year reveals whether your programme is actually working.

Why Estimate Instead of Test?

True 1RM testing requires a maximal attempt, which carries elevated injury risk on compound lifts. The most acutely dangerous moments in a barbell lifter's training year are typically the heavy singles in squat, bench, and deadlift — exactly the lifts most often tested.

For training-load prescription, an estimated 1RM within ±5% of true is functionally identical to a tested 1RM. The difference between programming at 84% vs 86% 1RM is smaller than the day-to-day variation in your real maximum (which fluctuates with sleep, hydration, stress, and where you are in the training cycle). For non-competing lifters, the upside of testing is small and the downside is large.

Powerlifters in active meet preparation are the obvious exception — they need to know the true value because the meet itself is a 1RM test. For everyone else, estimation is the more rational choice.

The Six 1RM Prediction Formulas

Each formula was developed from a different population and a different fitting procedure. They differ slightly in their treatment of high-rep performance, but at low rep counts (1–5) they produce nearly identical estimates.

Epley (1985)

1RM = weight × (1 + reps ÷ 30)

Published by Boyd Epley, longtime strength coach at the University of Nebraska, in his 1985 Boyd Epley Workout training manual. The most widely used 1RM formula. Tends to slightly overestimate 1RM at very low rep counts (1–2) and slightly underestimate at high rep counts (15+).

Brzycki (1993)

1RM = weight × 36 ÷ (37 − reps)

Published by Matt Brzycki in JOHPERD (1993). Highly accurate up to about 10 reps. Mathematically breaks down as reps approach 37 (denominator approaches zero), so don't apply it to high-rep sets.

Lander (1985)

1RM = weight ÷ (1.013 − 0.0267123 × reps)

Published by Jeff Lander in 1985. Often considered the most accurate across a broader 1–10 rep range, particularly in trained populations. Slightly more conservative than Epley at low reps.

Lombardi (1989)

1RM = weight × reps^0.10

A power-law form proposed by Vito Lombardi (1989). Less common in practice but produces estimates close to Lander at moderate rep counts (5–8).

O'Conner et al. (1989)

1RM = weight × (1 + 0.025 × reps)

Linear formula similar to Epley but with a smaller per-rep adjustment. Tends to produce conservative estimates, useful when you want a lower-bound number for training prescriptions.

Mayhew et al. (1992)

1RM = weight × 100 ÷ (52.2 + 41.9 × e^{−0.055 × reps})

Published by Mayhew, Ball, Arnold, and Bowen (1992) for the bench press specifically. Validated in subsequent studies as among the most accurate formulas for the bench press in both trained and untrained populations.

Formula Comparison Table

Estimated 1RM for a lifter benching 100 kg for various rep counts, all six formulas:

Reps	Epley	Brzycki	Lander	Lombardi	O'Conner	Mayhew
1	103	100	101	100	103	100
2	107	103	104	107	105	103
3	110	106	107	112	108	106
5	117	113	115	117	113	112
8	127	124	125	123	120	121
10	133	133	136	126	125	127
12	140	144	147	129	130	133

Notice how the formulas converge at low rep counts and diverge as reps increase. At 5 reps, the spread is just 5 kg (113–117). At 12 reps, the spread is 18 kg (129–147). This is the key practical takeaway: for accurate 1RM estimation, test at 2–5 reps.

RPE / RIR Adjustment for Submaximal Sets

The formulas above assume your test set was taken to true muscular failure — the point at which you couldn't complete another rep with proper form. In practice, most training sets stop short of failure, with reps in reserve (RIR) for safety, programme demands, or practicality.

To correct for this, use the RPE (Rate of Perceived Exertion) scale developed by Mike Tuchscherer and validated by Helms et al. (2016):

RPE	Reps in Reserve (RIR)	Description
10	0	Maximum effort, no reps left
9.5	0–1	Could maybe squeeze one more
9	1	Definitely could have done one more
8	2	Two reps in reserve
7	3	Three reps in reserve
6	4+	Four or more in reserve (warm-up territory)

To adjust your prediction:

Effective reps = actual reps + (10 − RPE)

Example: 5 reps at RPE 8 → effective reps = 5 + 2 = 7. Plug 7 into Epley with the same weight: 1RM = weight × (1 + 7 ÷ 30) = weight × 1.233. The KineticMetrix 1RM calculator applies this adjustment automatically when you provide RPE.

Worked Examples

Example 1 — Powerlifter testing for a meet attempt

A powerlifter benches 140 kg for 3 reps at RPE 9. Effective reps = 3 + 1 = 4. Using the Epley formula:

1RM = 140 × (1 + 4 ÷ 30) = 140 × 1.133 = 158.7 kg

Brzycki gives: 140 × 36 ÷ (37 − 4) = 152.7 kg. Lander: 140 ÷ (1.013 − 0.0267123 × 4) = 154.4 kg. Three-formula average: ~155 kg. A reasonable opener attempt would be 145–148 kg (90–93% of estimate).

Example 2 — Hypertrophy lifter checking training loads

A bodybuilder squats 100 kg for 8 reps at RPE 8 (2 RIR). Effective reps = 8 + 2 = 10. Epley: 100 × (1 + 10 ÷ 30) = 133 kg. Brzycki: 100 × 36 ÷ 27 = 133 kg. Three-formula average: ~134 kg.

Their 70% hypertrophy work would now be programmed at 0.70 × 134 = 94 kg for 8–12 reps, rather than guessing.

Example 3 — Beginner with high-rep test

A novice deadlifts 80 kg for 12 reps to failure. Epley: 80 × (1 + 12 ÷ 30) = 112 kg. Brzycki: 80 × 36 ÷ 25 = 115 kg. The two formulas agree closely, but at this rep count the underlying assumption (that fatigue per rep is uniform) is shakier. The true 1RM may be 5–10 kg lower than the formula predicts because untrained lifters have proportionally more high-rep endurance than 1RM strength.

The fix: re-test at 3–5 reps with a heavier load once they've done a few weeks of strength work.

Percentage-of-1RM Training Reference

Once you have your 1RM, you can prescribe training intensity precisely. The classical Prilepin-derived reference table:

% of 1RM	Approx. Reps	Training Goal	Typical Use
95–100%	1–2	Peak strength / testing	Meet preparation, peaking blocks
90–95%	2–3	Maximal strength	Heavy singles & doubles
85–90%	3–5	Strength & power	Standard heavy work
75–85%	5–8	Strength + hypertrophy	The strength sweet spot
70–80%	8–12	Hypertrophy	Bodybuilding volume
60–70%	12–20	Muscular endurance	Higher-rep work, conditioning
40–60%	15+	Power / speed-strength	Dynamic effort, technique

1RM Estimation by Lift Type

Formula accuracy varies by exercise. The general pattern:

• Bench press, squat, deadlift, overhead press: Formula error ~5% at low reps. Most validation studies tested these lifts.
• Other compound barbell lifts (rows, pulls): ~5–7% error. Comparable accuracy.
• Isolation exercises (curls, lateral raises, leg curls): ~10% error. Smaller muscle groups have different fatigue curves.
• Bodyweight exercises (pull-ups, dips): ~10–15% error. Load can't be incremented finely; test sets often span very different effort levels.
• Olympic lifts (snatch, clean & jerk): formulas not validated. Skill-dominant lifts where rep performance doesn't predict singles cleanly.

For the squat in particular, formulas can underestimate 1RM in well-trained lifters because the squat allows more reps at any given % of 1RM than the bench press. Lander and Mayhew adapt better to this; Epley tends to underpredict squat 1RM in very strong lifters.

1RM for Bodyweight Exercises (Pull-Ups, Dips)

Estimating "1RM" for pull-ups or dips is conceptually similar but requires accounting for body weight as part of the load:

True load = body weight + added weight
1RM (added weight) = (true load × Epley factor) − body weight

Example: a 75 kg lifter does pull-ups at +25 kg for 5 reps. Total load = 100 kg. Epley estimated 1RM total: 100 × 1.167 = 116.7 kg. Predicted weighted-pull-up 1RM = 116.7 − 75 = +41.7 kg.

Bodyweight-only test (no added weight): if you can do 8 strict pull-ups, your 1RM is approximately your body weight × 1.27 = 95 kg total load (so you could theoretically add 20 kg for one rep). In practice, pull-up 1RM estimates carry larger errors than barbell estimates because the test conditions vary more (kipping, range of motion, grip).

Limitations of 1RM Calculators

Three honest caveats:

1. Individual variation. Some lifters have unusually good muscular endurance (more reps at any % of 1RM) or unusually poor endurance (fewer reps). Untrained lifters tend to have proportionally more endurance than 1RM strength, so formulas overestimate their true 1RM. Highly trained powerlifters with neural specialisation for low-rep work may have actual 1RMs slightly higher than formulas predict.

2. Day-to-day variation. Real 1RM swings ±5–8% with sleep, stress, hydration, time of day, and where you are in the training cycle. This is larger than typical formula error. Don't chase the last kilogram of estimate precision.

3. Formula assumes muscular failure. If your test set was stopped early — for safety, programme demands, or fear — the formula will underpredict. Use the RPE adjustment described above to correct for this.

How Often to Recalculate

For a structured training programme, recalculate your 1RM:

• End of each training block (typically 4–8 weeks). Test at 3–5 reps to recalibrate.
• After significant body weight changes — gaining or losing 3+ kg can shift relative strength substantially.
• After a layoff longer than 2 weeks. Detraining drops 1RM faster than rep performance, so old numbers will be wrong.
• When a specific lift's progression stalls. Sometimes the issue is an outdated 1RM — your work weights have crept up to true 90% rather than the prescribed 75%, and your fatigue is masking growth.

Sources

1. Epley, B. (1985). Poundage chart. In Boyd Epley Workout. Lincoln, NE: Body Enterprises.
2. Brzycki, M. (1993). Strength testing — predicting a one-rep max from reps-to-fatigue. JOHPERD, 64(1), 88–90. DOI: 10.1080/07303084.1993.10606684
3. Lander, J. (1985). Maximum based on reps. NSCA Journal, 6, 60–61.
4. Lombardi, V.P. (1989). Beginning weight training: the safe and effective way. WC Brown.
5. O'Conner, B., Simmons, J., & O'Shea, P. (1989). Weight Training Today. West Publishing.
6. Mayhew, J.L., Ball, T.E., Arnold, M.D., & Bowen, J.C. (1992). Relative muscular endurance performance as a predictor of bench press strength in college men and women. Journal of Applied Sport Science Research, 6(4), 200–206.
7. LeSuer, D.A., McCormick, J.H., Mayhew, J.L., Wasserstein, R.L., & Arnold, M.D. (1997). The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research, 11(4), 211–213. JSCR link
8. Wood, T.M., Maddalozzo, G.F., & Harter, R.A. (2002). Accuracy of seven equations for predicting 1-RM performance of apparently healthy, sedentary older adults. Measurement in Physical Education and Exercise Science, 6(2), 67–94. DOI: 10.1207/S15327841MPEE0602_1
9. Helms, E.R., Cronin, J., Storey, A., & Zourdos, M.C. (2016). Application of the repetitions in reserve-based rating of perceived exertion scale for resistance training. Strength & Conditioning Journal, 38(4), 42–49. DOI: 10.1519/SSC.0000000000000218
10. Reynolds, J.M., Gordon, T.J., & Robergs, R.A. (2006). Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. Journal of Strength and Conditioning Research, 20(3), 584–592. DOI: 10.1519/R-15304.1