SnapMyGym
Free one-rep-max calculator using the Epley, Brzycki, and Lombardi formulas. Estimate your squat, bench, or deadlift 1RM from any heavy set — no signup.
Your one-rep max (1RM) is the heaviest weight you can lift for a single rep with good form. Almost every proven strength program — 5/3/1, GZCLP, Texas Method, Starting Strength — prescribes working weights as a percentage of it, so an accurate estimate is the first number you need before you can train with real intent.
Epley (weight × (1 + reps ÷ 30)) is the most widely used equation and tracks well for 2–10 reps. Brzycki (weight × 36 ÷ (37 − reps)) runs slightly conservative at higher reps, and Lombardi (weight × reps^0.10) favors low-rep, heavy sets. Each formula carries a bias at different rep ranges, so this calculator averages all three for a more stable estimate than any single equation.
For the best estimate, use a recent set of 2–6 reps taken close to failure. Above 10 reps every 1RM formula loses accuracy, because muscular endurance and fatigue — not maximal strength — become the limiting factor.
Most strength work happens between 75% and 90% of 1RM, and most hypertrophy work between 65% and 80%. Percentage-based programs like 5/3/1 don't even use your true max — they prescribe from a training max of 85–90% of your 1RM so every planned rep stays fast and repeatable.
You rarely need to test a true single. Re-estimate from your heaviest working sets every few weeks instead: it carries nearly all of the signal with none of the injury risk of a max-out day.
| Reps | % of 1RM | Example (300 lb / 140 kg 1RM) |
|---|---|---|
| 1 | 100% | 300 lb / 140 kg |
| 2 | 97% | 290 lb / 136 kg |
| 3 | 94% | 280 lb / 132 kg |
| 4 | 92% | 275 lb / 129 kg |
| 5 | 89% | 265 lb / 125 kg |
| 6 | 86% | 260 lb / 120 kg |
| 8 | 81% | 240 lb / 113 kg |
| 10 | 75% | 225 lb / 105 kg |
| 12 | 71% | 215 lb / 99 kg |
| 15 | 64% | 190 lb / 90 kg |
Within about ±5% when you estimate from a hard set of 2–6 reps, which is accurate enough to set training percentages. Accuracy drops sharply above 10 reps, and very experienced lifters tend to slightly out-lift what the formulas predict on grinding singles.
A recent set of 3–5 reps taken within 1–2 reps of failure is the sweet spot — heavy enough to reflect maximal strength, submaximal enough to be safe and repeatable.
Most percentage-based programs run better off a training max of 85–90% of your estimated 1RM. 5/3/1 uses 90% by design; the buffer keeps bar speed high and lets you progress for months without missing reps.
For most lifters, never — re-estimate from your working sets instead. If you compete or simply want to test, 2–3 times a year at the end of a peaking block is plenty.
Want the number to actually go up? Snap My Gym builds percentage-based programs around your lifts and tracks them automatically. More evidence-first training articles on the blog.