§1 · How it works.
This calculator uses the Epley formula with constant C=36. RIR is added to reps to compute total reps to failure before applying the formula: e1RM = weight × (1 + (reps + RIR) / 36). 1RM estimation algorithm →
§2 · Accuracy.
Epley estimates are most accurate at 6-15 reps. At rep counts above 20, most formulas overestimate. For precision, use submaximal rep ranges and track e1RM over multiple sessions; single-point estimates have high variance.
§3 · Track e1RM across every session.
This calculator gives a single estimate. Calyber Labs tracks e1RM automatically from every logged set, builds a calibration history, and adjusts your next prescription accordingly.
START FREE →Common questions.
- What is a one-rep max (1RM)?
- The maximum weight you can lift for exactly one full repetition of an exercise with proper form.
- What is RIR?
- Reps in Reserve: the estimated number of additional reps you could have completed before failure. RIR 0 = failure reached; RIR 3 = three reps left.
- Which formula does this calculator use?
- The Epley formula with constant C=36, calibrated for submaximal rep ranges of 6-15 reps. Formula: e1RM = weight × (1 + (reps + RIR) / 36).
- How accurate is 1RM estimation?
- Most validated at 6-15 reps. Accuracy decreases above 20 reps. Treat it as an estimate: direct 1RM testing with appropriate warmup is more precise.
- Why does Calyber track e1RM across sessions?
- e1RM computed from every session creates a calibration baseline. When performance increases or decreases, Calyber adjusts the next prescription automatically.