1RM Calculator

Your one-rep max is the most weight you can lift once with good form. Programs prescribe working weights as percentages of it, so it anchors almost everything in strength training. Testing it for real is fatiguing and carries some risk, which is why most lifters estimate it from a heavier set of several reps instead.

No single formula wins across the board. Validation studies find the best one shifts by exercise, sex, and rep range. Mayhew and Wathen tend to grade well on bench, Wathen on squat, and nearly every formula underestimates the deadlift. That is why this calculator headlines the average of all seven and shows you the spread.

Tell the calculator how many reps you had left. Every formula assumes the set ended at failure. Stop a set of 5 with 2 in reserve and your effort was worth 7 reps. The calculator adds your reps in reserve to your completed reps before running the math, which keeps the estimate honest.

Two to five. Accuracy is highest at low reps and softens past about ten, where muscular endurance starts to matter more than maximal strength. A heavy set of 3 to 5 taken close to failure gives the tightest estimate.

Each row shows the weight you could lift for exactly that many reps, based on your estimated max. Programs written in percentages translate straight off the chart: 3 sets of 3 at 90% becomes a plate-loaded number. These rows are all-out efforts, so everyday working sets should sit a little below the chart value.

An estimate is safer and nearly as useful for most lifters. A true test needs a thorough warm-up, a spotter or safety bars, and experience bailing on a missed rep. Powerlifters peaking for a meet test under those conditions. Everyone else does fine estimating from a heavy set of 3 to 5 and re-checking every few weeks.