One Rep Max Calculator
Use this free One Rep Max Calculator to calculate your 1RM estimate instantly and accurately.
Your set
Estimated 1RM
What is a One Rep Max Calculator?
A One Rep Max (1RM) Calculator estimates the maximum weight you can lift for a single repetition of an exercise. By entering the weight you lifted and the number of reps performed, it calculates your estimated 1RM using proven strength formulas.
How to calculate 1RM manually (the formula)
Epley formula: 1RM = weight × (1 + reps / 30).
Brzycki formula: 1RM = weight × 36 / (37 − reps).
This calculator averages both formulas for a more reliable estimate. For a set of 80 kg for 5 reps: Epley = 80 × (1 + ⅙) = 93.3 kg. Brzycki = 80 × 36 / 32 = 90.0 kg. Average = 91.7 kg.
Example calculation
You bench press 80 kg for 5 reps: Epley 1RM = 80 × (1 + 5/30) = 80 × 1.167 = 93.3 kg. Brzycki 1RM = 80 × 36 / (37 − 5) = 80 × 36 / 32 = 90.0 kg. Estimated 1RM = (93.3 + 90.0) ÷ 2 ≈ 91.7 kg.
Common mistakes
- Using a set with too many reps — Formulas are most accurate for 10 or fewer reps. Beyond that, endurance dominates and the estimate becomes unreliable.
- Not using proper form on the test set — If your technique breaks down, the weight you lifted does not reflect true strength. Always use strict form for the estimation set.
- Attempting a true 1RM too often — Testing your actual 1RM is neurologically and systemically taxing. Use estimated 1RM for most training cycles and test only periodically.
Frequently asked questions
What is a one-rep max (1RM)?
Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. It is the gold standard for measuring maximal strength.
How is 1RM calculated?
This calculator uses both the Epley formula (1RM = weight × (1 + reps/30)) and the Brzycki formula (1RM = weight × 36/(37 − reps)), then averages them for a reliable estimate.
How accurate are 1RM estimation formulas?
Estimates are most accurate for sets of 10 or fewer reps. Above 10 reps, muscular endurance rather than strength becomes the limiting factor, and formulas tend to overestimate.
Should I test my actual 1RM?
Testing a true 1RM carries injury risk and requires a spotter. Using a submaximal set (3–10 reps) to estimate your 1RM is safer and nearly as useful for programming.
How do I use my 1RM for training?
Most strength programs prescribe percentages of your 1RM. For example, 70–80% for hypertrophy (8–12 reps), 80–90% for strength (3–6 reps), and 90%+ for peaking (1–3 reps).
Can I use this calculator for any lift?
Yes, 1RM formulas work for any compound lift — bench press, squat, deadlift, overhead press, etc. However, technique-dependent lifts may have less accurate estimates.