How many reps per set to build muscle?

Short answer: for muscle, the rep range matters far less than it seems — high, moderate and low loads produce similar hypertrophy¹. For strength, it does: heavy load wins¹². With one condition that almost never gets quoted, and that holds the whole thing up: sets have to be taken close to failure.

§1Two big reviews, same answer

In 2017, a systematic review with meta-analysis pooled 21 studies comparing low load (≤60 % of your max) with high load (>60 %). The conclusion: maximal strength comes from heavy weight, while hypertrophy can be achieved across the whole loading spectrum².

In 2021, a network meta-analysis — which compares several loads at once instead of two — got to the same place by another route: no differences in hypertrophy between loads, in the overall analysis or by subgroup; and for strength, high and moderate load ahead of low¹.

§2The condition nobody quotes

"The range doesn't matter" is half a sentence. The 2017 review says it in its methods: every set in the included studies was taken to momentary muscular failure². Which makes sense, because that is what equalises what is actually being compared.

At 5 reps you get close to the limit almost by accident: the load forces it. At 25 you have to want it — and it is very easy to stop when the burn starts and finish six reps short of failure. That set doesn't count the same, and not because high reps are bad, but because the effort wasn't the same.

How close to failure you train does move the needle for hypertrophy³, and that is what the reps-in-reserve article is about.

§3How to use it

Pick the range by logistics and joints, not by metabolic magic:

6-12 reps is the comfortable default: enough load for the effort to arrive on its own, sets short enough to do several. 3-6 for the big lifts if you're after strength, or if your technique falls apart over many reps. 15-30 for whatever wrecks a joint under heavy weight — isolation work, machines, extensions — as long as you genuinely get close to failure.

And what doesn't change with the range: the weekly sets for that muscle. Ten sets of squats at 5 reps and ten at 20 both count as ten sets. That is the variable that does run the show.