How to Estimate Your One-Rep Max
Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. It's the foundation of percentage-based training programs — but actually testing your 1RM is risky, especially without a spotter. The solution? Estimate it from a submaximal set using a proven formula.
The Epley Formula
If you bench press 185 lbs for 5 reps: 185 × (1 + 5/30) = 185 × 1.167 = ~216 lbs. This formula is most accurate for sets of 2–10 reps. Beyond 10 reps, accuracy drops because muscular endurance becomes a larger factor than raw strength.
Using Your 1RM for Training
Most strength programs prescribe weights as a percentage of 1RM:
- 90–100%: Maximal strength (1–3 reps) — powerlifting peaks
- 80–90%: Strength (3–5 reps) — the bread and butter of strength training
- 70–80%: Hypertrophy (6–12 reps) — bodybuilding range
- 60–70%: Muscular endurance (12–20 reps)
- 50–60%: Speed/power work, warm-up sets
Pro Tip: Use your estimated 1RM as a training max, not a competition max. Many programs (like 5/3/1) recommend using 85–90% of your estimated 1RM as your "training max" to leave room for progress and prevent burnout.
Other 1RM Formulas
The Epley formula is the most widely used, but other validated formulas exist:
- Brzycki: 1RM = Weight × 36 ÷ (37 – Reps). More conservative, especially at higher rep ranges.
- Lander: 1RM = (100 × Weight) ÷ (101.3 – 2.67123 × Reps)
- Lombardi: 1RM = Weight × Reps^0.10
All formulas give similar results in the 2–6 rep range and diverge beyond 10 reps. Our calculator uses Epley because it's simple, well-researched, and matches real-world results for most lifters.
Common Mistakes
1. Using Sloppy Reps
The formula assumes proper form on every rep. If your last 2 reps are half-reps or required a spotter, the estimate will be inflated. Only count full-range, unassisted reps.
2. Testing After Fatigue
Your submaximal set should be fresh — first working set of the day, not after 5 sets of heavy squats. Accumulated fatigue lowers your rep count and underestimates your true 1RM.
Watch Out: A 1RM estimate is just that — an estimate. Never load a bar with your estimated max and attempt it cold. If you need a true 1RM for competition, work up gradually (singles at 85%, 90%, 95%) with a spotter or safety bars in place.
Use the calculator above to estimate your 1RM and get a full percentage chart for programming your training. Lift smart, lift safe.