What is a one rep max?
A one rep max (1RM) is the heaviest weight someone can lift for a single repetition with good form. Coaches use it to set training loads, usually as a percentage: 80% of 1RM for strength work, for example.
Testing a true 1RM takes a long warm-up, carries more injury risk and leaves the lifter tired. Estimating it from a hard set of a few reps is faster and safer, and close enough for programming.
How this 1RM calculator works
Enter the weight and the number of reps from a hard set. The calculator estimates the 1RM with three common formulas. The headline number uses Epley, the formula TrainBlock uses for estimated 1RM in the app.
- Epley
- 1RM = weight × (1 + reps ÷ 30)
- Brzycki
- 1RM = weight × 36 ÷ (37 − reps)
- Lombardi
- 1RM = weight × reps^0.10
How accurate is an estimated 1RM?
Estimates are most reliable from heavy sets of about 2–10 reps taken close to failure. The more reps in the set, and the further it stops from failure, the less accurate the estimate.
Accuracy also depends on the exercise. A 1997 study of seven prediction equations in college students found estimates closely tracked tested maxes on the bench press and squat, but every equation underestimated the deadlift (LeSuer et al., 1997, Journal of Strength and Conditioning Research). Treat the number as a starting point and adjust from how the lifts feel.
How coaches use 1RM to program
Most programs prescribe loads as a percentage of 1RM. Common ranges:
- 85–100% for 1–6 reps: maximal strength
- 67–85% for 6–12 reps: muscle growth and strength
- Under 67% for 12+ reps, or for fast reps: muscular endurance, technique and power
- Recalculate every few weeks from recent sets, so loads keep pace with progress
Many coaches pair percentages with reps in reserve (RIR): the percentage sets the starting load, and the RIR target adjusts it on the day.
Track estimated 1RM for every client
TrainBlock calculates estimated 1RM and strength records from the sets your clients log, so you can see progress without testing. Launching January 2027, and the first 100 coaches get 6 months free.
Questions
What is the most accurate 1RM formula?
No single formula is best for every lifter and exercise. Epley and Brzycki give similar results for sets of up to about 10 reps. Use the same formula each time, so changes in the number reflect real progress.
How many reps should I use to estimate my 1RM?
A hard set of about 2–10 reps works best. Estimates from higher-rep sets are less reliable.
Is it safe to test a true 1RM?
For experienced lifters with good technique, a well-warmed-up 1RM test with a spotter is generally safe. For newer lifters and most general clients, an estimated 1RM gives the information you need with less risk and fatigue.
How often should I recalculate my 1RM?
Every 4–6 weeks, or at the start of each training block, using recent hard sets.