Epley, Brzycki and Lombardi: how the formulas differ
All three turn a weight and a rep count into a one-rep-max estimate, but each uses a different curve. Epley, 1RM = weight x (1 + reps / 30), is linear and the most widely used. Brzycki, 1RM = weight x 36 / (37 - reps), is also linear but rises more steeply as reps climb. Lombardi, 1RM = weight x reps raised to the 0.10 power, follows a gentle power curve. For 100 lb lifted for 5 reps they give about 117 lb (Epley), 113 lb (Brzycki) and 117 lb (Lombardi), so the spread is small at low reps and widens as the rep count grows.
Which formula to choose
Epley and Brzycki give the same number at about 10 reps. Below 10 reps Epley reads slightly higher than Brzycki, and above 10 reps Brzycki reads higher. Lombardi stays close at low reps but reads lower as reps rise. Because estimates are most reliable from sets of roughly 2 to 6 hard reps, where all three nearly agree, the formula you pick matters less the closer you are to a true max. Choose one and stay with it so changes reflect real strength gains, not a switch in math.
Using your estimated max
Once you have a 1RM estimate, you can program your training around it. Strength work often uses 85% and above for low reps, hypertrophy work sits around 67% to 85% for moderate reps, and lighter loads build endurance. Re-test with a fresh submaximal set every few weeks to keep your percentages current as you get stronger.
Getting a good estimate
For the most reliable number, use a weight you can lift for about 2 to 6 hard reps with solid form, ideally the last set leaving little in reserve. Very high rep sets stray from true maximal strength and inflate the estimate. Keep the exercise, formula and conditions consistent so changes reflect real progress.