RPE calculator (RPE / RIR to 1RM)
Did 80 kg for 5 with about two reps left in the tank (RPE 8)? The calculator turns that into an estimated 1RM and suggests the weight for the next set — say, 3 reps at RPE 9.
Weight for the next set
Weight: 87.5 kg
RPE chart: % of 1RM
The well-known RPE chart (Tuchscherer / RTS). Highlighted — your set.
| RPE \ Reps | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 10 | 100 | 95.5 | 92.2 | 89.2 | 86.3 | 83.7 | 81.1 | 78.6 | 76.2 | 73.9 | 70.7 | 68 |
| 9.5 | 97.8 | 93.9 | 90.7 | 87.8 | 85 | 82.4 | 79.9 | 77.4 | 75.1 | 72.3 | 69.4 | 66.7 |
| 9 | 95.5 | 92.2 | 89.2 | 86.3 | 83.7 | 81.1 | 78.6 | 76.2 | 73.9 | 70.7 | 68 | 65.3 |
| 8.5 | 93.9 | 90.7 | 87.8 | 85 | 82.4 | 79.9 | 77.4 | 75.1 | 72.3 | 69.4 | 66.7 | 64 |
| 8 | 92.2 | 89.2 | 86.3 | 83.7 | 81.1 | 78.6 | 76.2 | 73.9 | 70.7 | 68 | 65.3 | 62.6 |
| 7.5 | 90.7 | 87.8 | 85 | 82.4 | 79.9 | 77.4 | 75.1 | 72.3 | 69.4 | 66.7 | 64 | 61.3 |
| 7 | 89.2 | 86.3 | 83.7 | 81.1 | 78.6 | 76.2 | 73.9 | 70.7 | 68 | 65.3 | 62.6 | 59.9 |
| 6.5 | 87.8 | 85 | 82.4 | 79.9 | 77.4 | 75.1 | 72.3 | 69.4 | 66.7 | 64 | 61.3 | 58.6 |
| 6 | 86.3 | 83.7 | 81.1 | 78.6 | 76.2 | 73.9 | 70.7 | 68 | 65.3 | 62.6 | 59.9 | 57.4 |
How to use it
- 1
Enter the set
Weight, reps and RPE — how hard it was: 10 is not one more rep, 8 is two left.
- 2
Get your 1RM
Reps in reserve are added to the ones you did: 5 reps at RPE 8 count as 7 to failure.
- 3
Pick a target
Reps and RPE for the next set — the calculator works out the weight in 2.5 kg steps.
What RPE and RIR are
RPE (rate of perceived exertion) rates how hard a set was, up to 10. In strength training it's tied to reps in reserve (RIR): RPE 10 — none left, RPE 9 — one, RPE 8 — two; the halves mean “maybe one more”.
The calculator estimates your 1RM with the same formula as LiftChat (Epley), adding the reserve to the reps done: 80 × 5 @ 8 → 80 × 7 to failure → ≈ 98.7 kg. The reverse is the same formula backwards.
The chart below is the well-known RPE chart popularised by Mike Tuchscherer (Reactive Training Systems): % of 1RM for each reps × RPE pair. Over 1–10 reps it differs from Epley by a couple of percent — a guide, not a law.
Your 1RM from every set, automatically
LiftChat estimates your 1RM from every logged set, charts it per lift and flags your records. The app doesn't log RPE yet — each set gets a form rating instead.
A new account gets 14 days of Standard right away: every feature, with half the assistant limit. No card and no auto-charge — after that you stay on the free plan, where workout logging has no limits.
1RM and records in LiftChat →Questions
What's the difference between RPE and RIR?
One scale seen from two ends: RIR is reps left in reserve, RPE = 10 − RIR. RPE 8 = 2 reps in reserve.
Where does the RPE chart come from?
It's a widely used chart popularised by Mike Tuchscherer (Reactive Training Systems): % of 1RM by reps and RPE, in half-RPE steps. We show it as a guide.
Why doesn't the calculator match the chart?
The estimate uses Epley, as in LiftChat, so your 1RM here and in the app is one number. The RPE chart is built differently; over 3–10 reps the gap is usually within 1–2 %.
Can I log RPE in LiftChat?
Not yet. Each set in LiftChat gets a form rating — clean, OK, cheating or dirty — and the 1RM comes from weight and reps.
How do I rate RPE well?
Honestly, right after the set. The closer the set is to failure (RPE 8–10), the more accurate the rating; on easy sets (RPE 6–7) the error is bigger.