One Rep Max (1RM) Calculator

Weights are rounded to the nearest 5 lb so they load cleanly on a bar. Rep targets are typical ranges, not rules: a grinder of a set of 5 at 85% and a crisp set of 5 at 85% are both normal.

Epley: 1RM = w × (1 + r / 30)

Brzycki: 1RM = w × 36 / (37 - r)

Lombardi: 1RM = w × r^0.10

O'Conner: 1RM = w × (1 + 0.025 × r)

Worked example: 225 lb for 5 reps. Epley gives 225 × (1 + 5/30) = 262.5 lb. Brzycki gives 225 × 36 / 32 = 253.1 lb. Lombardi gives 225 × 5^0.10 = 264.3 lb. O'Conner gives 225 × 1.125 = 253.1 lb. The average lands around 258 lb, and the 11 lb spread between the highest and lowest estimates is a fair picture of the uncertainty.

Which should you trust? Brzycki tracks tested maxes well at 5 reps or fewer. Epley and O'Conner behave better in the 6 to 10 rep range. Lombardi rises the most slowly, so it acts as a conservative check at higher reps. When they agree closely, the estimate is solid; when they spread wide, take the average with a grain of salt.

Most structured programs prescribe weights as a percentage of 1RM. The broad pattern: heavy work at 85 to 95% in sets of 2 to 6 builds maximal strength, moderate work at 65 to 80% in sets of 8 to 12 drives muscle growth, and lighter work below 60% for 15 or more reps trains endurance and technique.

A simple week for one lift might look like this: one heavy day at 85% for 5 sets of 3, one volume day at 75% for 4 sets of 8, and one light technique day at 60% for 3 sets of 10. All three days come straight off the percentage table above. When every prescribed weight starts moving fast, plug in a fresh set and let the numbers climb.

One caution: formulas estimate what you could lift for one perfect rep on a good day. Programming off 90 to 95% of your estimated max, sometimes called a training max, gives you room for bad days and keeps progress steady.

• Only count clean reps. A set of 5 with two ugly grinders is a set of 3 for estimation purposes.
• You don't need to attempt a true single to train with percentages. The estimate is the point.
• If you do test a real max: warm up thoroughly, use spotters or safety pins, and stop the session after a failed attempt rather than retrying it.
• New lifters should build a base with sets of 5 to 10 first. Estimated maxes change fast in the first months of training, and that is a good thing.