One Rep Max Calculator

Your one rep max (1RM) is the maximum amount of weight you can lift for a single repetition with correct form. It is the gold standard for measuring absolute strength in a given exercise and is used by strength coaches and athletes worldwide to program training.

Rather than actually attempting a true one-rep max, which carries injury risk, most lifters estimate their 1RM using submaximal testing. You simply perform a set to near failure with a lighter weight and plug the numbers into a formula. This gives you a reliable estimate without the risk of maxing out.

Knowing your 1RM lets you train with percentages. A coach might prescribe "5 sets of 3 at 85% of 1RM" — without knowing your max, that instruction is meaningless. This calculator gives you both the estimated max and a full percentage table for programming.

Brzycki: One of the most popular formulas, especially accurate for sets of 1–10 reps. It tends to slightly underestimate at higher rep ranges.

Epley: Another widely used formula that performs well across all rep ranges. It is the default in many strength training apps.

Lander: Similar accuracy to Brzycki but uses a different mathematical approach. Often gives slightly higher estimates.

Lombardi: Uses an exponential model rather than linear. Works well for moderate rep ranges.

O'Conner: A simpler formula that is easy to calculate mentally in the gym. Slightly less accurate at extreme rep counts.

We show the average of all five formulas for the most reliable estimate. The individual results give you a range to work within.

Strength training (1–5 reps): Work at 85–100% of your 1RM. This is the range that builds maximum force production. Rest 3–5 minutes between sets.

Hypertrophy (6–12 reps): Work at 67–83% of your 1RM. This is the sweet spot for muscle growth. Rest 1–2 minutes between sets.

Endurance (13–15+ reps): Work at 65% or below. This improves muscular endurance and work capacity. Rest 30–60 seconds between sets.

Recalculate your 1RM every 4–6 weeks as you get stronger. Small jumps in your estimated max indicate consistent progress.

How accurate is this? With 1–6 reps as input, estimates are typically within 5% of your actual 1RM. Accuracy decreases with higher rep counts because fatigue becomes a bigger factor.

Should I actually test my 1RM? For most people, estimating is safer and sufficient. True 1RM testing should only be done with a spotter, proper warm-up, and experience with heavy loads.

Why do the formulas give different numbers? Each formula models the relationship between reps and max strength differently. The variance is typically small (within 5%) for low rep counts but grows at higher rep ranges.

Do these formulas work for all exercises? They work best for compound barbell lifts like squat, bench, and deadlift. They are less reliable for isolation exercises, machines, or bodyweight movements.