☾ One Rep Max (1RM) Calculator
Estimate your one-rep max for any lift using Epley, Brzycki, and Lander formulas with a percentage chart.
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Start Free AI Coaching ✦🧬 How 1RM Estimation Works
Your one-repetition maximum (1RM) is the heaviest weight you can lift for a single rep with proper form. Instead of testing it directly (which carries injury risk), these formulas estimate it from a submaximal set you've already performed.
✦ Which 1RM formula is the most accurate? ↓
For lower rep ranges (2–6), the Brzycki formula tends to be most accurate. For higher reps (8–15), the Epley formula often performs better. The Lander formula sits in between. By averaging all three, you get the most reliable estimate across rep ranges.
✦ How should I use the percentage chart for training? ↓
Use 85–100% of 1RM for pure strength (1–6 reps), 65–85% for hypertrophy/muscle growth (6–12 reps), and 50–65% for muscular endurance (15–20+ reps). Periodize your training by cycling through these zones across your menstrual cycle phases.
✦ Does my 1RM change during my menstrual cycle? ↓
Yes! Research shows that maximal strength can be 5–10% higher during the late follicular/ovulatory phase when estrogen peaks. During the luteal phase, you may feel slightly weaker. Adjust your training intensity based on your cycle phase for optimal results and injury prevention.
✦ How often should I retest my 1RM? ↓
For intermediate lifters, retesting every 4–6 weeks is sufficient to capture meaningful strength changes. Beginners may see progress faster and can retest every 3–4 weeks. Always test during your follicular or early ovulatory phase when estrogen supports peak neuromuscular output — avoid maximal testing in the late luteal phase when fatigue and joint laxity are highest.
✦ Is it safe to test a true 1RM without a spotter? ↓
Testing a true 1RM alone is risky for barbell bench press, barbell back squats, and overhead presses. Use safety pins or a power rack with adjustable safeties. For machines and exercises like leg press or lat pulldown, the built-in safety mechanisms reduce risk significantly. Submaximal estimation (this calculator) is the safest alternative to a direct 1RM test.
✦ Why do different formulas give different results? ↓
Each formula was developed from regression analysis on different populations and rep ranges. Epley's formula (weight × reps × 0.0333 + weight) works best for 6–10 reps. Brzycki's (weight × 36 / (37 – reps)) is more accurate at 1–6 reps. Lander's formula sits between the two. Averaging all three compensates for individual variation and rep-range bias.
📖 How to Estimate Your One-Rep Max
Enter the weight you lifted and the number of reps you completed in a recent set (ideally 2–10 reps). The calculator runs three validated formulas — Epley, Brzycki, and Lander — and averages them for the most reliable estimate.
For best accuracy, use data from a set where you reached true technical failure or came within 1–2 reps of it. Sets of 3–6 reps produce the most accurate 1RM predictions; sets above 12 reps introduce progressively more estimation error.
📊 Understanding Your 1RM Estimate
The averaged 1RM is your estimated max for a single repetition with proper form. The percentage chart below translates this number into training loads for different goals: 90–100% for maximal strength (1–3 reps), 75–85% for hypertrophy (6–12 reps), and 60–70% for muscular endurance (15+ reps).
Formula differences are normal: Brzycki tends to be slightly conservative at low reps, while Epley runs slightly higher at moderate reps. The averaged value smooths these biases. Re-test every 4–6 weeks to track strength progression over time.
⚕️ When to Seek Medical Guidance
Do not attempt a true one-rep max test if you have a history of joint injuries, herniated discs, or uncontrolled blood pressure. If you experience sharp or shooting pain during any lift, stop immediately and consult a sports medicine physician or orthopedic specialist before resuming heavy training. Women in the ovulatory phase should be extra cautious about knee-dominant lifts due to increased ligament laxity.