One Rep Max: How to Calculate and Why It Matters

What 1RM is — and is not

Your one rep max is the heaviest weight you can lift for a single repetition with technically valid form. It is the benchmark that most strength programs use to prescribe loading: 70% of 1RM for strength-endurance work, 80 to 85% for pure strength, 90%+ for peak power and neurological development.

1RM is not a measure of how strong you are "overall" — different lifts produce different 1RMs, and strength on one movement does not fully predict strength on another. A 200 kg deadlifter might squat 140 kg and bench 100 kg. 1RM is lift-specific.

Crucially, 1RM does not have to be tested directly. Almost every well-designed strength program estimates 1RM from submaximal sets — usually a set of 3 to 8 reps with a hard, close-to-failure load. The formulas are accurate enough to program with, and much safer than grinding a true max.

The main formulas

Several equations convert a set of N reps at weight W into a 1RM estimate. The two most widely used:

Epley: 1RM = W × (1 + reps / 30)

Brzycki: 1RM = W × (36 / (37 − reps))

Epley was derived in 1985 and is slightly more conservative at high reps. Brzycki (1993) is slightly more generous at low reps. They agree very closely between 2 and 10 reps — usually within 2%.

Other formulas exist: Lander (1985), Lombardi (1989), O'Conner (1989), Mayhew (1992). They differ mainly in how they handle the 8+ rep range. For most strength programming, you will only be estimating from sets of 3 to 6, where all formulas converge. The choice does not matter much.

Worked example

A lifter does 5 reps on bench press at 100 kg — a hard, close-to-failure set.

• Epley: 1RM = 100 × (1 + 5 / 30) = 100 × 1.1667 = 117 kg
• Brzycki: 1RM = 100 × (36 / (37 − 5)) = 100 × 1.125 = 113 kg
• Average: ~115 kg

The same lifter doing 8 reps at 90 kg:

• Epley: 90 × (1 + 8 / 30) = 90 × 1.267 = 114 kg
• Brzycki: 90 × (36 / 29) = 90 × 1.241 = 112 kg

Both estimates are similar, and close to the 5-rep prediction — a good sign the estimate is accurate. When the same lifter's 3RM, 5RM, and 8RM all predict similar 1RMs, you can trust the number.

Rep-to-percent table

Derived from Epley, a useful mental table for converting between rep maxes and %1RM:

• 1 rep: 100%
• 2 reps: ~95%
• 3 reps: ~93%
• 5 reps: ~87%
• 6 reps: ~85%
• 8 reps: ~80%
• 10 reps: ~75%
• 12 reps: ~70%
• 15 reps: ~65%

Example: if your 1RM bench is 120 kg, a hard set of 5 should be around 105 kg (87% of 120). A top set of 8 should be around 96 kg. A warm-up of 10 could be around 90 kg.

Note that these percentages are averages. Individuals vary substantially. A lifter with strong muscular endurance may hit 10 reps at 80% of 1RM; another may fail at 6 reps with the same load. After a few training cycles, you learn your own rep-to-percent relationship, which matters more than the table.

When formulas break down

• Too many reps. Above 12 reps, muscular endurance dominates. A set of 20 reps tells you about endurance, not max strength, and 1RM predictions become unreliable.
• Too few reps, not to failure. The formulas assume a hard, close-to-failure set. If your 5-rep set could have been 8, the estimate is too low.
• Technical lifts at high loads. Olympic lifts (snatch, clean and jerk) have steeper strength drop-offs with reps. Dedicated Olympic-lifting formulas exist; powerlifting formulas overstate Olympic 1RMs.
• Beginners. Novices gain strength so fast that a 1RM estimated today may be 10 kg low in two weeks. Re-estimate frequently.

Using 1RM to actually program training

Classic percentage prescriptions for a given goal:

• Strength-endurance / hypertrophy: 65 to 75% for sets of 8 to 12.
• Hypertrophy / general strength: 75 to 85% for sets of 5 to 8.
• Pure strength: 85 to 92% for sets of 3 to 5.
• Peak / competition: 92%+ for singles and doubles, used sparingly.

A typical training week might include one heavy session at 85 to 90% for sets of 3, one moderate session at 75 to 80% for sets of 6, and one lighter session at 65 to 70% for sets of 8 to 10. The 1RM anchors all three.

As strength increases over months, your 1RM increases too. Re-estimate from a hard top set in training every 8 to 12 weeks, and update your working percentages. If your training max is 100 kg and you start hitting 5 at 90 kg easily, your 1RM is no longer 100 kg — recalculate.

Why testing matters less than you think

The main argument for testing a true 1RM is to have a precise number. In practice:

• The training effect of testing is minimal — it is just one very heavy single, without the volume that drives adaptation.
• The risk of form breakdown and injury is higher at 95 to 100% than at 85 to 90%.
• Estimated 1RM from a working set is within 3 to 5% of a true 1RM for most trained lifters, which is enough for programming.
• True 1RMs drift day to day with sleep, stress, and nutrition. The number you test Monday may not be the number you could hit Friday.

The lifters who actually need accurate 1RM testing are powerlifters before a meet, where knowing whether you can open at 200 kg or 210 kg matters. Everyone else can program off estimates with almost no cost to progress.

The short version

Pick a compound lift. Do 3 to 6 reps of a hard, close-to-failure set. Plug into Epley or Brzycki. That number is your working 1RM for programming. Retest every 8 to 12 weeks by doing another hard top set. Skip the true max attempts except on meet day.