Lift a weight that leaves you one to three clean reps short of failure on your working sets: RIR 1–3, which is RPE 7–9 on the reps-in-reserve scale. Then stop chasing percentage charts and let the bar follow what you actually did last session. Below: how to read your reps in reserve, how to find a starting weight with zero data, and when your own estimate deserves your trust.
How much weight should you lift?
There’s no answer in pounds or kilos. There’s an answer in effort. A lifter squatting 60 kg (132 lb) and one squatting 140 kg (309 lb) who both rack the bar with two good reps left are training at the same relative effort, even if their bars look nothing alike.
That’s the idea behind the RPE scale built on repetitions in reserve, laid out by Helms and colleagues in 2016. Instead of asking what’s on the bar, it asks one question: how many more clean reps did you have?
What do RPE and RIR mean?
- RIR (reps in reserve): how many clean reps you had left when you racked the bar.
- RPE (rating of perceived exertion): an effort score out of 10. In the RIR-based version, you read it straight off your reps in reserve.
“Clean” matters. A rep only counts if it looks like your first one. If you’d need to bounce out of the hole, shift onto your toes or cut depth to finish it, it isn’t in the tank.
How do RPE and RIR line up?
| RPE | RIR | What you’d say racking the bar |
|---|---|---|
| 10 | 0 | ”Nothing left. That was it.” |
| 9 | 1 | ”Maybe one more. Not two.” |
| 8 | 2 | ”Had two left.” |
| 7 | 3 | ”Had three left.” |
Short version: RPE = 10 − RIR. Aiming for RIR 1–3 means aiming for RPE 7–9.
Why not take every set to failure?
Because the payoff is small. A 2023 meta-analysis by Refalo and colleagues pooled 15 studies on muscle growth and found the advantage of training closer to failure was small at best (standardized effect estimates around 0.15 to 0.21), and trivial when comparing sets taken to failure with sets stopped short. For maximal strength, Helms and colleagues also caution against going to failure on a regular basis.
Grinding out every set to the last twitch isn’t the price of admission for growth.
How many reps, and how hard, for your goal?
| Goal | Load and reps | How close to failure | Source |
|---|---|---|---|
| Getting started | Loads of 8–12 RM, 2–3 days a week | Not specified | ACSM (2009) |
| Muscle size | 6–12 reps, 1–2 min rest, multiple sets | RPE 8–10 (RIR 0–2) depending on the phase; RPE 6–8 (RIR 2–4) on main lifts | Helms (2016), ACSM (2009) |
| Max strength | 80–100% of 1RM | Avoid regular failure | Helms (2016) |
| Muscular endurance | 40–60% of 1RM, more than 15 reps, under 90 s rest | Not specified | ACSM (2009) |
“8–12 RM” means a load you could lift at most 8 to 12 times. The RM sets the weight; RIR sets where you stop. On frequency, the ACSM suggests 2–3 days a week for novices, 3–4 for intermediates and 4–5 for advanced lifters.
Percentages only work if you know your 1RM. An estimated 1RM can fill that gap, but the RIR approach doesn’t need one at all.
How do you find your starting weight with zero data?
New lift, empty log, no max. That’s exactly where reps in reserve earns its keep.
- Ramp up through warm-up sets until the movement feels grooved and the bar starts to feel like something.
- Pick a conservative load for your first working set and do the planned reps.
- Rate your RIR right away, before you’ve had time to talk yourself out of it.
- Adjust:
- RIR 4 or more: too light. Add weight on the next set or next session.
- RIR 1–3: that’s your working weight. Keep it.
- RIR 0, or form breaking down before the last rep: too heavy. Strip some off.
Don’t expect to nail it on day one. The adjusting is the method.
Worked example: a squat from 60 to 72.5 kg
Dana is getting back into barbell squats and has never rated a set in her life. Her program calls for 3 sets of 8 at RIR 2.
Session 1. She loads a plate a side, 60 kg (132 lb), and gets her 8. Racking it, she figures she had 4 more: RIR 4, RPE 6. Too light for a working set.
Session 2. She goes to 70 kg (154 lb) for 8 and has two left in the tank: RIR 2, RPE 8. That’s her working weight.
Sessions 3 and 4. Still at 70 kg, her first set climbs to 9 reps at RIR 2, then to 10 reps at RIR 2 the session after. That’s 1–2 reps over target on two consecutive sessions, which is exactly the trigger in the ACSM’s 2009 progression rule: add 2–10% to the load.
| Option | Math | New load |
|---|---|---|
| +2% | 70 × 0.02 = 1.4 kg (3.1 lb) | 71.4 kg (157 lb) |
| +10% | 70 × 0.10 = 7 kg (15.4 lb) | 77 kg (170 lb) |
| Her pick | 70 + 2.5 kg (+3.6%) | 72.5 kg (160 lb) |
A 1.25 kg (about 2.75 lb) plate on each side puts her inside the range without reaching for the top of it.
Session 5. At 72.5 kg, the target resets to 8 reps at RIR 2. If she only gets 6 with two still in reserve, she stays at 72.5 kg and builds the reps back up before the next jump. That’s double progression in a nutshell: reps first, then load.
Where RIR falls short
Beginners’ estimates are rougher
Zourdos and colleagues (2016) tested the scale on 29 squatters, 15 experienced and 14 novices: a 1RM, then singles at 60, 75 and 90% of 1RM and a set of 8 at 70%. As bar speed dropped, RPE went up, with a strong correlation in both groups. But it was tighter in the experienced lifters (r = −0.88) than in the novices (r = −0.77).
If you’re new, treat your RIR as a working estimate to refine, not a measurement.
It gets fuzzier far from failure
“I had one left” is an easier call than “I had five left.” Keep working sets in the RIR 1–3 band, where the read is clearest. To calibrate, a common gym habit is to occasionally take the last set of a safe exercise (a machine, or a barbell with the safety arms set) to technical failure and compare it with your prediction.
It won’t manage fatigue for you
RIR tells you where to set the load today. It won’t tell you whether you need a deload week. If your weights keep sliding for several sessions at the same RIR, that’s the question to look at.
Persistent pain, an injury or a medical condition: see a healthcare professional before changing anything.
How does EXE handle this?
EXE is an AI coach for athletes, with a free tier that has no time limit. From your second session, it suggests working weights based on your logged history. Its auto-progression is rule-based: it looks at your recent sessions and suggests +1.25 or +2.5 kg, holding steady, or a deload. A session counts as successful when you complete at least 90% of the planned work at an RPE under 8.5. Your estimated 1RM is calculated with the Epley formula. See how EXE works.
FAQ
Should I use RPE or RIR?
They say the same thing. RIR is easier to use when you’re starting out (“how many did I have left?”), while RPE is what most written programs use. With RPE = 10 − RIR, switching between them takes no math.
When should I add weight?
The ACSM’s 2009 rule: when you beat your target by 1–2 reps on two sessions in a row, add 2–10%. On light dumbbells, the smallest jump can blow past that range: going from 10 kg to 12.5 kg (roughly 22 to 27.5 lb) is a 25% jump. When that happens, build reps first.
Do you need to train to failure to build muscle?
No. Refalo and colleagues (2023) found only a small advantage, at best, for getting closer to failure, and a trivial difference between sets to failure and sets stopped short. Leaving 1–3 reps in the tank is a sensible default for working sets.
My RIR guesses are way off. What now?
That’s normal early on: in the Zourdos study, the scale tracked effort less closely in novices. Log your RIR every set and check it against a true failure set on a safe exercise now and then. Reading effort is a skill, like technique.
Sources
- Application of the Repetitions in Reserve-Based Rating of Perceived Exertion Scale for Resistance Training — Helms et al., 2016: the RPE/RIR mapping and effort ranges for size and strength.
- Novel Resistance Training–Specific Rating of Perceived Exertion Scale Measuring Repetitions in Reserve — Zourdos et al., 2016: how well the scale tracks effort in experienced and novice lifters.
- Influence of Resistance Training Proximity-to-Failure on Skeletal Muscle Hypertrophy: A Systematic Review with Meta-analysis — Refalo et al., 2023: failure vs non-failure training for muscle growth.
- Progression Models in Resistance Training for Healthy Adults — ACSM, 2009: load ranges by goal, training frequency and the 2–10% progression rule.
