Why estimate instead of test
A true one-rep max needs a warm-up, spotters, fresh legs and a willingness to fail under a heavy bar. An estimate from a set of three to five reps is safer, quicker and — for programming — about as useful, since training percentages are approximate anyway. Enter a recent set taken to or near failure with good form; sets of two to six reps give the most accurate estimates, and anything above ten drifts because muscular endurance varies so much between people.
| Reps | Epley | Brzycki | Lombardi | O'Conner |
|---|---|---|---|---|
| 1 | 233 | 225 | 225 | 231 |
| 2 | 240 | 231 | 241 | 236 |
| 3 | 248 | 238 | 251 | 242 |
| 5 | 262 | 253 | 264 | 253 |
| 8 | 285 | 279 | 277 | 270 |
| 10 | 300 | 300 | 283 | 281 |
| 12 | 315 | 324 | 288 | 292 |
The formulas
Epley's equation first appeared in his Boyd Epley Workout poundage chart (Body Enterprises, Lincoln, Nebraska, 1985); Brzycki published a reps-to-fatigue prediction method in 1993. LeSuer and colleagues (Journal of Strength and Conditioning Research, 1997) tested these and the Lombardi, O'Conner, Mayhew and Wathan equations against measured 1RM in the bench press, squat and deadlift: correlations were high (r > 0.95), but most equations were biased for at least one lift and all under-estimated the deadlift. Reynolds and colleagues found that prediction accuracy depended on repetition count and exercise in their bench-press and leg-press study. Those findings do not validate averaging all six formulas for every lifter; the average here is a planning estimate, not a tested maximum.
Epley (1RM = w × (1 + r ÷ 30)) and Brzycki (1RM = w × 36 ÷ (37 − r)) are the two most used; they agree at 10 reps and differ by a few percent elsewhere, Epley reading higher below 10 reps and lower above. Lombardi, O'Conner, Mayhew and Wathan were fitted to different populations and lifts. The calculator shows all six and averages them, which smooths out any single formula's bias. Differences between formulas are smaller than day-to-day variation in your own strength.
- Epley: w × (1 + r/30)
- Brzycki: w × 36 / (37 − r)
- Lombardi: w × r^0.10
- O'Conner: w × (1 + 0.025 r)
- Mayhew: 100 w / (52.2 + 41.9 e^(−0.055 r))
- Wathan: 100 w / (48.8 + 53.8 e^(−0.075 r))
Sources: Journal of Strength and Conditioning Research 11(4):211–213: The Accuracy of Prediction Equations for Estimating 1-RM Performance in the Bench Press, Squat, and Deadlift (LeSuer, McCormick, Mayhew, Wasserstein & Arnold; Epley, Brzycki, Lombardi, O'Conner, Mayhew and Wathan equations); Journal of Physical Education, Recreation & Dance: Strength Testing—Predicting a One-Rep Max from Reps-to-Fatigue; Journal of Strength and Conditioning Research: Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry
Training percentages
Programs prescribe loads as a percentage of 1RM, and each percentage corresponds roughly to a number of reps you could do with it. The calculator's table converts your estimated max into those loads, rounded to the plates available. The table below is a conventional rounded chart rather than an exact formula output (Epley itself gives 85.7% at 5 reps and 75% at 10); individuals vary by a rep or two either way, and lower-body lifts usually allow more reps at a given percentage than upper-body lifts.
| Reps | % of 1RM | Weight (lb) | Weight (kg) |
|---|---|---|---|
| 1 | 100% | 300 | 136 |
| 2 | 95% | 285 | 129 |
| 3 | 93% | 279 | 127 |
| 4 | 90% | 270 | 122 |
| 5 | 87% | 261 | 118 |
| 6 | 85% | 255 | 116 |
| 8 | 80% | 240 | 109 |
| 10 | 75% | 225 | 102 |
| 12 | 70% | 210 | 95 |
Intensity zones
Different goals live in different percentage bands. Maximal strength needs heavy singles to fives above 85%; hypertrophy programs mostly work 65–80% for six to twelve reps; endurance and technique work sits below 65%. Most well-designed programs spend time in more than one zone across a training cycle.
| Goal | % of 1RM | Reps | Notes |
|---|---|---|---|
| Max strength | 85–100% | 1–5 | Powerlifting peaking; low volume |
| Strength | 80–90% | 3–6 | Most strength programs live here |
| Hypertrophy | 65–80% | 6–12 | Muscle growth with moderate loads |
| Endurance | < 65% | 12+ | Conditioning, technique, rehab |
Example: a four-week strength block
With an estimated 300 lb max, a simple linear block raises intensity weekly and drops volume, finishing with a test or a heavy single. Re-estimate the max after the block from the heaviest set of three to five you completed, and program the next block from the new number.
| Week | Sets × reps @ % | Load (lb) |
|---|---|---|
| Week 1 | 3 × 5 @ 80% | 240 |
| Week 2 | 3 × 3 @ 85% | 255 |
| Week 3 | 3 × 2 @ 90% | 270 |
| Week 4 | Test or 1 @ 95% | 285 |
Limits of the estimate
Formulas assume the set was a true near-maximal effort; a set stopped with two reps in reserve under-estimates your max. They are calibrated mostly on the bench press and squat in trained lifters; deadlifts and Olympic lifts, which are limited by technique or grip, fit less well. Beginners' estimates change quickly as skill improves. And a max is a snapshot — sleep, food, stress and the previous day's training all move it by a few percent.