How to Calculate Your One Rep Max
Your one rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. It's the foundation of percentage-based training and the most common way to measure absolute strength. But you don't need to actually test your 1RM to know it - and in most cases, you shouldn't.
The Epley Formula - Estimated 1RM
The most widely used formula for estimating your 1RM from a submaximal set is the Epley formula:
e1RM = Weight x (1 + Reps / 30)
For example, if you bench press 80kg for 8 reps: e1RM = 80 x (1 + 8/30) = 80 x 1.267 = 101.3kg. Your estimated one rep max is about 101kg.
This formula is most accurate between 1-10 reps. Above 10 reps, it tends to overestimate your true 1RM because high-rep sets test muscular endurance as much as strength.
Why Estimated 1RM Matters More Than Testing
Testing your actual 1RM is risky and unnecessary for most lifters. A true max attempt requires a specific peaking protocol (tapering volume for 1-2 weeks), carries a much higher injury risk than submaximal training, and takes days to recover from. It's useful for powerlifting competition prep. For everyone else, your estimated 1RM from regular training sets gives you the same information with zero risk.
More importantly, e1RM trends are the best indicator of real strength progress. If your estimated 1RM is increasing over time, you're getting stronger - regardless of what happens on any single max-out day. A single max attempt is a snapshot. An e1RM trend line is the full picture.
How to Track e1RM for Progress
The most effective way to use e1RM is to track it across sessions for each major lift. Every time you do a working set of bench press, your app calculates the e1RM from that set. Over weeks and months, you can see whether your bench press e1RM is trending up (you're progressing), flat (you've plateaued), or down (you're regressing).
This is far more useful than checking whether you added 2.5kg to the bar. You might be lifting the same weight but doing more reps - which means your e1RM went up even though the bar weight didn't change. That's real progress that would be invisible without e1RM tracking.
Other 1RM Formulas
Brzycki formula: e1RM = Weight x (36 / (37 - Reps)). Tends to give slightly lower estimates than Epley, especially at higher rep ranges.
Lander formula: e1RM = (100 x Weight) / (101.3 - 2.67123 x Reps). Similar accuracy to Epley for sets of 1-10 reps.
In practice, the differences between formulas are small (1-3%). Pick one and stick with it for consistency. Epley is the industry standard and what most training apps use.
When to Actually Test Your 1RM
Test your true 1RM only when you have a specific reason: preparing for a powerlifting meet, validating your estimated max after a long training block, or setting a baseline at the start of a new programme. Even then, limit max testing to 2-3 times per year. More than that adds fatigue and injury risk without meaningful benefit.