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How Heavy Should You Lift? RPE and Reps in Reserve, Explained

Get That Shape AI · Updated 2026-08-10

"Lift heavy" is the most repeated and least useful advice in the gym. Heavy compared to what? For most people the real question is much more practical: standing in front of a rack, which number do I put on the bar today — and how do I know it was right? That's what RPE and reps in reserve answer.

Start with the rep range, not the weight

Pick the rep range your goal calls for, then find the weight that fits it. Not the other way round.

• Strength — 3 to 6 reps. Heavier loads, longer rests (2–4 minutes), fewer total reps. Best for getting stronger at a specific movement.
• Muscle size — 6 to 15 reps. The bulk of hypertrophy work lives here. Rests of 90 seconds to 2 minutes.
• Muscular endurance — 15 to 30 reps. Useful for conditioning and for joints that dislike heavy loads. Still builds muscle if taken close enough to failure.

The important nuance: all three ranges build muscle, provided the set is taken reasonably close to failure. Anywhere from 5 to 30 reps produces similar growth when effort is matched. The ranges differ in what else they give you — strength, or conditioning, or joint comfort — and in how unpleasant they are. Most people find 6–12 the sweet spot for that reason alone.

Reps in reserve: the scale that makes this concrete

RIR is simply how many more reps you could have done if you'd kept going. RPE (rate of perceived exertion) is the same idea on a 1–10 scale, where RPE 10 means nothing left.

• RIR 0 / RPE 10 — absolute failure. The next rep does not happen.
• RIR 1 / RPE 9 — one more was possible, and only one.
• RIR 2 / RPE 8 — two more. The bar is slowing noticeably.
• RIR 3 / RPE 7 — three more. Hard, but under control.
• RIR 4+ / RPE 6 or lower — warm-up territory. Little growth stimulus.

Train most of your sets at RIR 1–3. That's the band where the stimulus is essentially maximal and the fatigue cost is still manageable. Below RIR 4, growth drops off fast; at RIR 0 on every set, the fatigue you accumulate starts eating the next session.

Picking your first working weight

If you've no idea where to start on an exercise, do this once:

• Choose a weight you're confident you can do 10 times. Deliberately underestimate.
• Do the set and stop at 10, then ask honestly: could I have done three more? Five more?
• If you had 5+ left, add 10–20% and try again after a rest. If you had 3–4 left, add 5–10%. If you had 1–2 left, that's your working weight.

Two attempts is usually enough. Don't burn a whole session hunting for a perfect number — the plan will correct itself over the next two weeks anyway.

A three-week example

Dumbbell bench press, target 3 sets of 8–10 at RIR 2. You start with 22.5 kg dumbbells.

• Week 1 — 22.5 kg: 10, 9, 8 reps. The last set felt like RIR 1. Good starting point, don't change anything.
• Week 2 — 22.5 kg: 10, 10, 10. All three sets ended at RIR 2–3. You've cleared the top of the range on every set, so next week you add load.
• Week 3 — 25 kg: 9, 8, 7. Back to the bottom of the range at RIR 1–2. Exactly right. Stay here until you're hitting 10, 10, 10 again.

That's the whole method: work up to the top of the rep range across all sets, then increase the weight and fall back to the bottom. Repeat indefinitely. The mechanism behind it is covered in progressive overload explained — this article is just the practical dial for setting the number.

Why not train to failure on everything?

Failure is not the goal; a strong stimulus with recoverable fatigue is. Going to true failure on every set:

• Costs disproportionate fatigue for a small extra stimulus, especially on big compound lifts.
• Degrades your later sets. Failing on set one means sets two and three are much worse — total quality volume goes down.
• Wrecks technique exactly when the load is heaviest and the risk is highest.

A reasonable default: compound lifts at RIR 2–3, isolation work at RIR 0–1. A set of lateral raises taken to failure costs you almost nothing systemically. A set of squats taken to failure costs you the rest of the session.

Your RIR judgement is probably wrong at first

Nearly everyone new to this overestimates how close they are. Told to stop at RIR 2, most beginners stop with five or six reps still available. There's a simple calibration test:

• Take a moderate weight on a safe exercise — a machine, or dumbbells you can drop.
• Do the set to the point where you'd normally call it RIR 2, then keep going to actual failure and count the extra reps.
• If you got five more, your internal scale is off by three. Adjust and retest in a few weeks.

Run this once per major movement pattern. It's the single fastest way to make everything else in this article work.

Adjusting on a bad day

Some days the prescribed weight simply isn't there — poor sleep, stress, an unusually hard week. RIR handles this gracefully: keep the effort constant and let the weight move. If 80 kg feels like RIR 0 when it should feel like RIR 2, drop to 70 kg and finish the session with quality sets. That is not failure. That is auto-regulation, and it's exactly why the scale exists.

The opposite also applies. If the prescribed set finishes at RIR 4 and the bar is flying, add weight immediately rather than waiting for next week.

Common mistakes

• Adding weight before earning it. If your rep count drops every week, you went up too fast. Sit at a load until it's genuinely comfortable at the top of the range.
• Never adding weight. Far more common. If the same dumbbells feel identical after two months, the plan has stopped being a plan.
• Counting reps you didn't control. Half-range reps with a bounce aren't reps. Set your RIR by the last one you could do properly.
• Ego-loading the first set. Sets two and three tell the truth. A 6, 4, 3 session is a weight problem, not a stamina problem.
• Using the same RIR for everything. Heavy compounds and small isolations deserve different treatment, as above.

Where this fits in your plan

Rep ranges and RIR are the two dials that turn a list of exercises into a program. Everything else — which exercises, which days, how many sets — is structure, and structure without a load rule just produces the same workout forever. If you're still assembling that structure, start with how to build a workout plan and come back to this for the numbers.

How this changes as you get more experienced

The scale stays the same; how fast the numbers move does not.

• First six months — you can often add weight every single week, sometimes every session on the big lifts, because your nervous system is learning as fast as your muscles are growing. Take it while it lasts.
• Six months to two years — weekly jumps stop working. Expect to sit at a load for two or three weeks before the whole set range comes up. This is normal and not a plateau.
• Beyond two years — progress becomes monthly and increasingly indirect: an extra rep here, a set added there, better technique, shorter rests at the same load. The bar moving up is one form of progress among several.

This is also where the smallest available plates start to matter. A 2.5 kg jump on a 40 kg bench is a 6% increase — steep. If your gym has 1.25 kg or 0.5 kg plates, use them; if not, add a rep instead and take the weight jump once you're at the top of the range on every set. The advanced lifter's version of progressive overload is mostly patience with smaller increments, not different methods.

Get That Shape AI does this calculation for you: every set arrives with a target weight and rep range derived from the sets you actually logged, so the load moves when you've earned it and holds when you haven't. Start your free trial and get a plan that adjusts itself.