Free Tool · Strength Training
1RM Calculator
Estimate your one-rep max from any working set. Enter weight and reps, optionally add RIR, and get target weights for every rep range from singles to sets of 15.
RIR is the number of reps you left in the tank. Logging it improves accuracy for sets taken close to failure.
How it works
Two formulas, one answer
Epley's formula converts any set into an estimated 1RM using the equation 1RM = weight × (1 + reps / 30). It works well for sets in the 2 to 10 rep range and is the most widely cited estimator in strength literature.
The RPE chart adds a second signal by asking how hard the set actually was. When you log RIR, we convert it to RPE (10 minus RIR) and read the percentage of 1RM directly from a validated RPE-to-percent table. The higher of the two estimates is your working 1RM.
Both methods have known blind spots. Epley underestimates for low-rep sets and overestimates for high-rep sets. RPE breaks down when effort is guessed rather than felt. Using both prevents either blind spot from dominating the result.
How to use the %1RM table
Program every rep range from one number
Once you have an estimated 1RM, the percentage table tells you what to load for any rep target. For strength work (1 to 5 reps), use 85 percent or higher. For hypertrophy (6 to 12 reps), use 65 to 85 percent. For endurance (12+ reps), drop below 65 percent.
The weights are rounded to the nearest 2.5 pounds so they map cleanly to standard plates. If you train in kilograms, we convert to pounds for rounding, then convert back so the plate math still works on most commercial racks.
Frequently asked questions
Questions we hear a lot
Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. It is the standard reference point for strength programming. Most lifters never test a true 1RM; instead, they estimate it from sets at lower weights.
We use Epley's formula: 1RM = weight × (1 + reps / 30). If you also provide RIR (Reps in Reserve), we cross-check with the RPE chart and use the higher of the two estimates. Epley's is accurate within about 3 percent for sets in the 2 to 10 rep range.
Epley's formula is most accurate in the 2 to 10 rep range and within 2 reps of failure. Accuracy drops for very high rep sets (15+) and for sets taken well short of failure. For best results, use sets where you stopped within 2 reps of failure (RIR 0 to 2).
RIR is how many more reps you could have done before failing. RIR 2 means you stopped with two reps left. Logging RIR lets us use an RPE-based 1RM estimate that accounts for how hard the set actually was, not just the numbers on the bar.
Most lifters should not. Testing a true max is stressful on joints and the central nervous system, and a calculated estimate from a heavy set of 3 to 5 is plenty accurate for programming. Save max attempts for meet day or planned strength tests.
Every 4 to 6 weeks during a focused strength or hypertrophy block, or any time you hit a clear performance jump. If you are tracking in the Sculpt AI app, it recalculates automatically after every logged set.