One-Rep Max Formulas
Two formulas are most commonly cited in strength research:
- Epley (1985): 1RM = Weight × (1 + Reps/30) — best for moderate rep ranges (4–12)
- Brzycki (1993): 1RM = Weight × 36/(37 − Reps) — slightly more conservative; strong agreement at 6–10 reps
This calculator shows both and averages them for the percentage table. The fewer reps you use for the test set, the more accurate the estimate — use a 3–5RM test for best results.
Training Zone Reference
| % 1RM | Reps | Primary Adaptation |
|---|---|---|
| 90–100% | 1–3 | Maximum strength, peaking |
| 80–90% | 3–5 | Strength & power |
| 70–80% | 6–8 | Strength / hypertrophy (optimal zone) |
| 60–70% | 8–12 | Hypertrophy (muscle size) |
| 50–60% | 12–20 | Muscular endurance |
How to Test Safely
- Warm up with 3–5 progressive sets before the test set
- Use 3–5 reps for accuracy; never test a true 1RM without a spotter and experience
- Rest 3–5 minutes between warm-up sets
- 1RM estimates lose accuracy above 10 reps — the error compounds quickly
Frequently Asked Questions
How accurate are 1RM formulas?
At 3–5 reps, error is typically ±2–5%. At 10+ reps, error can exceed 10%. For programming purposes, the estimate is close enough to set training zones.
Should I actually test my 1RM?
Only if you have proper technique, a spotter, and a competitive reason. Most lifters are better served by estimating from a 3–5RM test and using the percentage table for programming.
Does 1RM differ between exercises?
Yes. Your squat 1RM is independent of your bench press 1RM. Test each lift separately. Fatigue from one test can affect others, so limit to 2 exercises per session.