Weekly set count per muscle is the most useful single number in hypertrophy programming, and it is the one most programs never state explicitly, which is why people run a plan for months without knowing what dose they are actually taking.
The number
Ten to twenty hard sets per muscle per week is the range the evidence supports for most people. Within it:
Under 10: works, particularly for beginners, and leaves some growth unclaimed. A perfectly reasonable choice if time is genuinely limited, and better than an ambitious plan you abandon.
10 to 20: the productive band. Most well-designed programs land here for the muscles they prioritise.
Over 20: some people respond, most see the returns flatten while fatigue keeps accumulating. Worth reserving for a deliberate specialisation block rather than running permanently across every muscle.
Why splitting it matters more than the total
Sixteen sets for chest in one session is worse than eight and eight across two, for two reasons.
Set quality collapses. By set twelve you are producing far less stimulus per set than you were at set three, so the last third of a long session is mostly fatigue.
Each session restarts the response. Muscle protein synthesis rises after training and returns to baseline within a day or two. Two exposures raise it twice.
Which is the actual argument behind training each muscle roughly every 48 to 72 hours, and behind choosing a split by recovery windows rather than preference: push pull legs vs upper lower.
Counting indirect volume
Your triceps work hard on every press and your biceps on every row. If you count only what you did in a movement named after the muscle, you will systematically undercount arms and shoulders.
The usual approximation is to count indirect involvement as roughly half a set. It is crude, and it is much closer than ignoring it. This is also exactly what a per-muscle involvement model does properly: our exercise catalog carries an involvement weight per muscle for each of 173 movements, so a bench press deposits full load on chest and a fraction on triceps and delts rather than being tagged with one label.
Where the number should differ
Small muscles tolerate more frequency, large compound movements cost more systemically. Ten sets of squats is a different proposition from ten sets of lateral raises.
Prioritise, do not maximise. Running twenty sets for everything is how you end up unable to recover from any of it. Pick two or three muscles to push and hold the rest at maintenance.
Your recovery capacity is the ceiling. Sleep, food and life stress set how much volume is productive, not the research average.
On how hard those sets should be, see should you train to failure.