How do I calculate my E1RM (estimated one rep max)?
Understanding your estimated 1-rep max (E1RM) is essential for effective strength training. The E1RM tells you the maximum weight you could theoretically lift for a single repetition, based on a set you've already performed. This guides your workout intensity, helps you set progressive overload targets, and lets you track strength gains across different rep ranges.
What Is an E1RM?
An estimated one-rep max (E1RM) is a calculated prediction of the maximum weight you could lift for exactly one repetition. Rather than attempting a dangerous maximal lift, you perform a set at a submaximal weight — say, 5 or 8 reps — and plug those numbers into a formula.
This is especially useful for:
- Programming training percentages — most strength programs prescribe work as a percentage of 1RM (e.g., "75% of 1RM for 5×5")
- Tracking strength progress over time without frequent maximal testing
- Comparing lifts across different sessions and rep ranges
The E1RM Formulas
Exercise scientists have developed multiple formulas for estimating the one-rep max. Each uses the weight lifted and the number of reps completed:
- Brzycki Formula: 1RM = Weight / (1.0278 - (0.0278 × Reps))
- Epley Formula: 1RM = Weight × (1 + (0.0333 × Reps))
- Lombardi Formula: 1RM = Weight × (Reps^0.10)
- Mayhew Formula: 1RM = (100 × Weight) / (52.2 + (41.9 × e^(−0.055 × Reps)))
- O'Conner Formula: 1RM = Weight × (1 + (0.025 × Reps))
- Wathan Formula: 1RM = (100 × Weight) / (48.8 + (53.8 × e^(−0.075 × Reps)))
These are documented on the Wikipedia page for one-repetition maximum.
A Step-by-Step Example
Say you squat 225 lb for 5 reps. Here's what each formula estimates as your 1RM:
The results cluster around 253–267 lb — a useful working range for setting your training percentages.
Which Formula Is Most Accurate?
It depends on your rep range:
- Brzycki and Epley are the most widely used and generally most accurate for sets in the 2–10 rep range. Brzycki tends to be slightly more conservative.
- Mayhew and Wathan use exponential functions and perform better at higher rep ranges (10–20 reps).
- Lombardi is the simplest and tends to overestimate slightly, especially at higher reps.
- O'Conner produces the most conservative estimates across all rep ranges.
As a general rule: the closer your working set is to 1 rep, the more accurate any formula will be. E1RM estimates become increasingly unreliable beyond 10 reps — there's simply too much variability in muscular endurance between individuals.
How to Use Your E1RM in Training
Once you have your estimated 1RM, you can use it to prescribe percentage-based working sets:
- 90–95% of 1RM → 1–2 rep sets (near-maximal strength)
- 80–85% of 1RM → 3–5 rep sets (strength focus)
- 70–75% of 1RM → 6–10 rep sets (strength and hypertrophy)
- 60–65% of 1RM → 12–15 rep sets (hypertrophy and endurance)
Most popular strength programs — Starting Strength, 5/3/1, GZCLP — build their progression around these percentages.
Try the Calculator
Existing one-rep max calculators often hide which algorithm they're using. The Strength Journeys One Rep Max Calculator shows you all six formulas simultaneously so you can compare results and choose the one that fits your training method — it's science!