One-Rep-Max

Estimating a Single-Rep Max From a Lighter, Multi-Rep Set

A one-rep max (1RM) is the heaviest weight you could lift for a single repetition, estimated from a lighter weight you’ve already lifted for multiple reps. Enter the weight lifted and how many reps it took, and this calculator shows the estimate from three long-standing published formulas, plus their average.

None of these formulas is more “correct” than the others — they’re each independently derived and can disagree meaningfully, especially at higher rep counts, which is why all three are shown rather than picking one as the answer.

The Formula

Every formula below uses the same two inputs — weight lifted and reps completed — so the same two colors track the same two quantities across all three:

$$\text{Epley (1985): 1RM} = \vA{\text{Weight}} \times \left(1 + \frac{\vB{\text{Reps}}}{30}\right)$$ $$\text{Brzycki (1993): 1RM} = \vA{\text{Weight}} \times \frac{36}{37 - \vB{\text{Reps}}}$$ $$\text{Lombardi (1989): 1RM} = \vA{\text{Weight}} \times \vB{\text{Reps}}^{0.10}$$

These formulas are calibrated against sets of roughly 1–10 reps — estimates at much higher rep counts become increasingly unreliable, and Brzycki’s formula specifically becomes mathematically invalid at 37 reps or more.

Worked Example

Lifting 200 lbs for 5 reps:

1. Epley: $200 \times (1 + 5 \div 30) \approx 233.3 \text{ lbs}$
2. Brzycki: $200 \times 36 \div (37 - 5) = 225 \text{ lbs}$
3. Lombardi: $200 \times 5^{0.10} \approx 234.9 \text{ lbs}$
4. Average: $\approx 231.1 \text{ lbs}$

Key Factors to Consider

• These formulas are most reliable in the 1-10 rep range they were originally calibrated against. Estimating a one-rep max from a set of 15-20+ reps stretches the formulas well outside the range they were derived from, and the resulting estimate becomes progressively less trustworthy the further outside that range the input set falls.
• A one-rep max estimate is typically used for programming training percentages, not as a lift to actually attempt. Many strength-training programs express working weights as a percentage of 1RM (e.g. “work at 75% of your 1RM for this block”) — the estimate is more useful for this planning purpose than as a literal target to test outright.
• The specific lift matters — a 1RM estimate from one exercise doesn’t transfer to another. A squat, bench press, and deadlift each have their own distinct strength curve and technique demands, so an estimate calculated from one lift’s rep data only estimates a max for that same lift, not for a different movement.
• Fatigue, warm-up quality, and technique on the day of the tested set all affect how well an estimate holds up. A set performed with fresh energy and clean form produces a more reliable estimate than one performed fatigued or with breakdown in technique near failure, since the formulas assume the reps performed genuinely reflect the lifter’s true strength on that movement.

Common Mistakes

• Using a set taken close to failure with breakdown in form. A rep count where technique started to fall apart near the end doesn’t reflect the lifter’s genuine strength as cleanly as a crisp set with a rep or two left in reserve.
• Applying an estimate from one lift to a completely different one. As noted above, a 1RM estimated from squat data says nothing about deadlift or bench press strength — each lift needs its own tested (or estimated) set.
• Treating the estimate as a number to attempt immediately. These formulas are best used to set training percentages for programming, not as a green light to load the bar to the estimated number without a proper warm-up and a spotter.
• Trusting an estimate from a very high rep set. As the FAQ above and the formula section note, accuracy degrades well outside the roughly 1-10 rep range these formulas were calibrated against.

Useful to Know

• Curious how your estimated strength compares pound-for-pound against your own body weight? Wilks / DOTS Score Calculator normalizes lifts for bodyweight comparison.
• Want to know your lean tissue mass alongside your strength numbers? Lean Body Mass Calculator estimates that from height, weight, and sex using a similar multi-formula approach.
• Tracking overall fitness alongside strength training? Calorie / TDEE Calculator estimates the calories your training and daily activity actually burn.