Strength training
Epley Formula: How to Calculate Your 1RM Step by Step
The Epley formula is the most popular way to estimate one-rep max without ever lifting a true limit weight.
What the Epley formula is and where it comes from
The Epley formula, proposed by Boyd Epley in 1985, is one of the most widely used methods to estimate one-rep max (1RM) from a submaximal set. Instead of asking your client to lift a limit weight with injury risk, you estimate their theoretical maximum from a weight they can move with solid technique.
Its popularity comes from a double virtue: it is easy to apply mentally and gives reasonable estimates across the rep ranges we use most in the gym. That is why it is the default in most strength calculators and training apps.
The formula and how to apply it step by step
The Epley equation is: 1RM = weight × (1 + reps / 30). You only need the weight lifted and the number of clean reps performed close to technical failure.
Here is a worked example. If a client squats 180 kg for 5 reps: 1RM = 180 × (1 + 5/30) = 180 × 1.1667 = roughly 210 kg. For a heavy reference set, Epley returns about 206.7 kg, a slightly higher estimate than other formulas.
The key step is rep honesty: reps should land within 0-1 of failure. A set with 3 or 4 reps in reserve artificially inflates the weight used and distorts the calculation.
When to use the Epley formula
Epley shines in the middle rep ranges, especially between 3 and 8 reps, where the load-rep relationship stays fairly linear. It is the default choice when you have no specific reason to prefer another.
Strength
Simple mental math and reliable results in the middle rep range, the most common in strength training.
Limitation
It tends to overestimate 1RM on very long sets (more than 12 reps), where fatigue is no longer linear.
Best use case
Sets of 3 to 8 reps on big lifts such as squat, deadlift and bench press.
Comparison with the other four formulas
No formula is perfect: each assumes a different model of the strength-endurance relationship. For the same heavy reference set, estimates differ: Epley returns about 206.7 kg, O'Conner 205 kg, Lander 202.8 kg, while Brzycki and Lombardi land around 200 kg.
Epley usually sits at the high end of the range because its linear model is slightly more generous as reps increase. That is why many coaches pair it with a more conservative formula like Brzycki to bracket an interval instead of trusting a single number.
How to use 1RM in your clients' programming
Once you have an estimated 1RM, you can prescribe loads by percentage: 70-80% for hypertrophy, 85-95% for maximal strength. Combining percentage with RPE or RIR lets you adjust day to day based on the client's real fatigue.
In TrainerStudio you store each exercise's estimated 1RM, generate target loads automatically and log every set to see how strength evolves week by week without losing track in spreadsheets.