RPE & RIR Calculator (% of 1RM)

A set of five at RPE 8. A lifter squats 140 kg for 5 reps and rates it RPE 8: two more reps were possible. The Helms et al. chart puts 5 reps at RPE 8 at 81 % of 1RM, so the estimated max is 140 ÷ 0.81 = 172.8 kg. Epley with 5 + 2 = 7 reps to failure agrees closely: 140 × (1 + 7 ÷ 30) = 172.7 kg.

A prescription: 5 @ 8 from a 200 kg max. 200 × 0.81 = 162 kg, which is 162.5 kg on the bar. For 10 @ 7 from a 150 kg max the chart has no cell, so the calculator uses Epley: 10 + 3 = 13 reps to failure, 100 ÷ (1 + 13 ÷ 30) = 69.8 %, and 150 × 0.698 = 104.7 kg.

The common mistake: treating a set with reps left as a max set. Put 140 kg × 5 into an ordinary 1RM formula and Epley gives 140 × (1 + 5 ÷ 30) = 163.3 kg, because it assumes the fifth rep was the last possible one. At RPE 8 two reps were left, so the honest estimate is 172.8 kg — 9.5 kg higher.

Rating of perceived exertion began with Gunnar Borg’s scales for endurance exercise. For lifting, a scale anchored to how many reps were left first appeared in Mike Tuchscherer’s Reactive Training Manual (Reactive Training Systems, 2008), written for powerlifters. Michael Zourdos and colleagues brought it into the research literature in “Novel resistance training-specific rating of perceived exertion scale measuring repetitions in reserve” (Journal of Strength and Conditioning Research, 2016): 10 is maximum effort, 9 means 1 rep remaining, 8 means 2, 7 means 3, and 5–6 means 4–6. In 29 squatters they found experienced lifters rated a true 1RM higher than novices (9.80 against 8.96) and that bar speed fell as the rating rose.

Eric Helms, John Cronin, Adam Storey and Zourdos then showed how to programme with it in “Application of the repetitions in reserve-based rating of perceived exertion scale for resistance training” (Strength and Conditioning Journal, 2016). Their Table 2 — the chart used here — links reps, RPE and percentage of 1RM. It is anchored on the experienced squatters’ average ratings for singles at 90 and 100 % of 1RM and for 8 reps at 70 % — the three cells printed in bold in the paper (100 % for 1 @ 10, 91 % for 1 @ 8, 70 % for 8 @ 7); every other cell is an estimate, and the authors warn it is a guide to the relationship, not an exact conversion, because individuals and days differ.

This calculator uses the published Helms et al. chart where it has a value (RPE 7–10, 1–8 reps) and, outside it, Epley’s formula with reps to failure equal to reps done plus reps in reserve — marked on the grid and in the table so you always know which one you are reading. You can switch to Epley everywhere for one consistent curve. It estimates a max from any set you rate, gives the load for any reps × RPE prescription rounded to the bar, and lists loads from 1 to 12 reps at RPE 10, 9, 8, 7 and 6.

Everything runs in your browser; nothing you enter is sent anywhere. For general information only — not medical advice. Talk to a doctor or other qualified professional about your own health.

Related tools: One-Rep Max (1RM) Calculator, Barbell Plate Calculator, and Wilks & DOTS Powerlifting Score Calculator.