One-Rep Max (1RM) Calculator
Enter a weight you've lifted and how many reps you completed with it to estimate your one-rep max (1RM) — the heaviest weight you could likely lift for a single rep, using the widely used Epley formula.
How the One-Rep Max (1RM) formula works
The Epley formula:
1RM = Weight × (1 + Reps / 30)
Step-by-step calculation
- Divide the number of reps completed by 30.
- Add 1 to that result.
- Multiply by the weight lifted to estimate your one-rep max.
Worked example
Lifting 185 lb for 5 reps: 1RM = 185 × (1 + 5/30) = 185 × 1.1667 ≈ 216 lb.
Frequently asked questions
How accurate is the Epley formula?
It's a widely used, reasonably reliable estimate for rep ranges up to about 10-12 reps, but accuracy decreases at higher rep counts, since the relationship between reps and maximum strength isn't perfectly linear at very high repetitions.
Should I actually attempt my calculated 1RM?
This is an estimate, not a guarantee — attempting a true one-rep max carries real injury risk and is generally recommended only with proper warm-up, form, and often a spotter, particularly for less experienced lifters. Many lifters use the estimate for training percentage calculations rather than attempting the actual lift.