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RPE 8 at 5 reps is 81.1% — the chart knows, now so do you.
Autoregulation only works if the conversion is instant: an estimated 405 lb 1RM and a target of RPE 8 × 5 means 330 on the bar — 81.1% per the Tuchscherer chart. This calculator reads the chart for you, interpolates half-RPE steps, and rounds to plate-friendly numbers.
Lifters use it at the rack: RPE 8 × 5 on a 405 e1RM is 330 on the bar — the Tuchscherer chart, half-steps interpolated, plates rounded.
RPE 8 means you finish the set with exactly 2 reps left in the tank — "reps in reserve" is the operational definition that made RPE useful for lifting. The Tuchscherer chart converts that to a percentage: RPE 8 × 5 reps is 81.1% of 1RM, because a true 5-rep max (RPE 10) is 86.3%, and each rep in reserve shifts the cell one column. The calibration trick every lifter should steal: periodically take a warm-up set to true failure and compare actual reps against predicted — if RPE 8 × 5 keeps producing 7 reps, your RPE 8 is really RPE 7.5 and the chart self-corrects within a few sessions.
They are the same system viewed from opposite directions — RPE IS percentages, adjusted for the day. Percentage programs assume your 1RM is fixed; RPE admits it moves ±5% with sleep, stress, nutrition, and accumulated fatigue. On a good day RPE 8 puts more weight on the bar than the spreadsheet would; on a bad day it protects the session. The research and two decades of RTS practice show autoregulated loads match or beat fixed-percentage programs for strength outcomes, mainly because they eliminate both junk-too-light days and grind-to-failure days. The honest answer: use percentages to plan the block, RPE to run the session.
The Tuchscherer chart bottoms out around 60% — below that, reps-to-failure stops mapping cleanly to percentage because endurance, fiber type, and technique efficiency dominate. A request like RPE 6 at 12 reps implies a load where individual variation swamps the table, so the honest answer is "unmapped" rather than a fake-precise number. If you need sub-60% work (deloads, speed work), program it by percentage directly or by velocity instead. The chart's useful range is roughly RPE 6.5–10 across 1–10 reps — inside that band it is the most battle-tested conversion in strength training.