Estimate your 1RM from a tested rep-max using 5 classic formulas.
| % of 1RM | Working weight | Typical reps |
|---|
Five rep-max formulas: Epley, Brzycki, Lander, Lombardi, O'Connor. They diverge above 8 reps; for accuracy, test in the 3–6 rep window. Always perform a true max attempt with a spotter.
The 1RM (one-rep maximum) is the heaviest weight you can lift once with correct form. It anchors strength training: programs prescribe sets at 70 %, 80 %, 90 % of 1RM, and progress is benchmarked against last cycle's 1RM. Testing a true 1RM is risky and rarely done outside competition because it requires near-maximal CNS recruitment, perfect form, a spotter, and a fully-recovered athlete. So instead, lifters extrapolate from a sub-maximal rep-max — say, 5 reps at 100 kg — using one of several rep-max formulas. Each formula was fit to a different population (powerlifters, weightlifters, military), and each handles different rep ranges with different accuracy. This calculator applies five widely-used formulas (Epley, Brzycki, Lander, Lombardi, O'Connor) and reports their average as a robust estimate, plus the percentage rep-range table that programs are written against.
Let w = weight lifted, r = reps performed. - Epley (1985): 1RM = w × (1 + r / 30). Linear in r; popular for general use, slightly over-estimates above 8 reps. - Brzycki (1993): 1RM = w × 36 / (37 − r). Hyperbolic; valid up to ~10 reps, becomes unstable beyond. - Lander (1985): 1RM = 100 × w / (101.3 − 2.67123 × r). Designed for collegiate athletes. - Lombardi (1989): 1RM = w × r^0.10. Power-law; smaller variance across rep ranges. - O'Connor (1989): 1RM = w × (1 + 0.025 × r). Conservative linear; good for beginners.
The five-formula average smooths individual quirks. The percentage-of-1RM rep table follows Prilepin's classic mapping (95 % → 2 reps, 90 % → 3–4, 85 % → 5–6, 80 % → 7–8, 75 % → 9–10, 70 % → 11–12, 60 % → 14–16). These are descriptive ranges, not prescriptions.
Enter the weight lifted and the rep count performed (1–12 — beyond 12 the formulas diverge sharply). Pick kg or lb to match your gym. The result panel shows the average 1RM as the headline plus the five individual formula outputs for transparency. The right-hand table converts the headline 1RM into working weights at 95 % / 90 % / 85 % / 80 % / 75 % / 70 % / 60 % with the typical rep ranges for each — the building blocks of any percentage-based program (5/3/1, conjugate, Texas method, …).
Bench press 100 kg × 5. - Epley: 100 × (1 + 5/30) = 100 × 1.1667 = 116.7 kg. - Brzycki: 100 × 36 / 32 = 112.5 kg. - Lander: 100 × 100 / 87.94 = 113.7 kg. - Lombardi: 100 × 5^0.1 = 117.5 kg. - O'Connor: 100 × (1 + 0.125) = 112.5 kg. - Average: 114.6 kg estimated 1RM. - Working sets at 80 % = 91.7 kg for 7–8 reps; at 90 % = 103.1 kg for 3–4 reps.
Reps × form. A formula assumes the reps were clean — full range of motion, controlled tempo, no bouncing or grinding. A 5 with the last 2 reps barely above the chest will inflate the estimate; tested in the 3–6 rep window with conservative form, the formulas are accurate to within 5 % for most lifters.
CNS fatigue. Estimating 1RM from a max-out rep-max set right after a heavy session inflates the implied 1RM because you were already fatigued. Test fresh; a same-day estimate from a top working set is fine; estimating from the third set of a hard session is not.
Bodyweight movements scale differently. Pull-ups, dips, push-ups don't follow these rep-max curves because adding weight is non-linear in effort. Use a separate "bodyweight + load" approach.
Beginner overestimation. Untrained lifters can grind out reps at 90 % 1RM that a trained lifter wouldn't — their nervous system isn't yet efficient at maximal recruitment. The formulas understate beginners' true 1RM by 5–15 % in the first six months. Re-test every 4–8 weeks.
Lift specificity. A 1RM bench from a 5RM is reliable; a 1RM squat from a 10RM is not — high-rep squats fatigue cardiovascularly before they fatigue the prime movers, and the formulas don't know that. Stay in the 3–6 rep window for accuracy on the big lifts.
Spotters and safeties. The estimate is for what you could lift, not what you should attempt. Always have safeties, a spotter, or both for any near-1RM attempt.