RPE calculator
Reviewed by Aaron Parry, strength and conditioning coach for RAF Rugby and Peterborough Rugby
Updated 26 October 2026
Enter the weight, reps and RPE of a set to estimate your one-rep max, then pick the reps and RPE you want next. RPE 8 means 2 reps left, so 100 kg for 5 at RPE 8 is 7 reps from failure: an estimated max of about 123 kg. For 3 reps at RPE 8 from that max, load about 105 kg.
How the RPE calculator works
On the lifting RPE scale, each point below 10 is one rep left in the tank: RPE 10 is no reps left, RPE 9 is one, RPE 8 is two (Zourdos et al., 2016). So a set tells you how many reps you could have done in total:
Reps to failure = reps done + (10 − RPE)
The calculator then uses the Epley formula, the same one the Lift Proven app uses:
Estimated max = weight × (1 + reps to failure ÷ 30)
To find the weight for a target, it runs the same sum backwards: weight = max ÷ (1 + (target reps + 10 − target RPE) ÷ 30), rounded down to a weight you can load (2.5 kg or 5 lb).
Worked example
- You squat 100 kg for 5 at RPE 8. That is 5 + 2 = 7 reps to failure.
- Estimated max = 100 × (1 + 7 ÷ 30) = 100 × 1.2333 = 123.3 kg.
- Next session asks for 3 reps at RPE 8: 3 + 2 = 5 reps to failure. Weight = 123.3 ÷ (1 + 5 ÷ 30) = 123.3 ÷ 1.1667 = 105.7 kg, so load 105 kg.
Limits, and why
- RPE 7 to 10 only for estimates. Lifters are more accurate at rating sets close to failure. Across 12 studies they underestimated their reps left by about one on average, and accuracy improved nearer failure and on sets of 12 reps or fewer (Halperin et al., 2022).
- Reps plus reps left must be 10 or fewer to estimate a max. Longer sets depend more on fitness than strength. The app applies the same two limits.
- It is an estimate. Some people get more reps at a given percentage than the formula expects, and some fewer. Published RPE charts from different coaches vary by a per cent or two for the same reason.
New to RPE? Read RPE and RIR explained for the full scale and how to rate your sets.
Rate your sets and let the coach set the weight
In Lift Proven, tap how hard a set felt from 7 to 10. Your estimated max sharpens, the app learns how accurate your ratings are, and it sets your next session.
Questions
- How do you calculate weight from RPE?
- Work out reps to failure (target reps + 10 − target RPE), then divide your estimated max by 1 + that number ÷ 30. For 3 reps at RPE 8 from a 123 kg max: 123 ÷ (1 + 5 ÷ 30) ≈ 105 kg.
- What percentage is RPE 8 for 5 reps?
- About 81% of your one-rep max, using the Epley formula: 5 reps plus 2 in reserve is 7 reps to failure, and 1 ÷ (1 + 7 ÷ 30) ≈ 0.81.
- What does RPE 8 mean?
- You finished the set with about 2 good reps left. RPE 9 means 1 left, and RPE 10 means none.
- Can I estimate my max from an RPE 7 set?
- Yes, as long as reps plus reps left come to 10 or fewer. Estimates from sets rated closer to 10 are more reliable, because people judge reps left better near failure.
- Is this the same RPE chart as other coaches use?
- It uses the same reps-in-reserve scale. Charts differ by a per cent or two because coaches fit them to different data; this one uses the Epley formula, the same as the Lift Proven app.