The range that shows up in the research
Across the published training-volume literature, somewhere between 10 and 20 hard sets per muscle group per week is where most lifters build muscle fastest. Below 10, you're usually leaving growth on the table. Above 20, you're mostly adding fatigue without adding much extra stimulus, unless you're advanced and recover unusually well.
That's a wide range on purpose. The right number for you depends on training age, how well you recover, how close to failure each set is, and how many muscle groups you're trying to grow at once.
Why beginners need less than they think
A true beginner grows on shockingly little volume, sometimes 6 to 10 sets a week per muscle, because almost any consistent stimulus is new stimulus. Piling on 20 sets from week one usually just buries you in soreness and makes the next session worse, not better. Start low, and add sets only when the same volume stops producing results.
Why "more sets" stops working
Every extra set costs recovery capacity. Past a point, that cost outweighs the extra growth stimulus, and total weekly performance starts to slide, not improve, because you're never fully recovering between sessions. This is the single most common reason intermediate lifters stall: not too little volume, but too much of it for what their recovery can actually support.
How to find your actual number
Start in the middle of the range, around 12 to 14 sets. Hold it for three to four weeks. If strength and reps are still climbing at the same weight, you're recovering fine, add a set or two per muscle and repeat. If reps start drifting down at the same weight, or every session feels harder than it should, you've gone past your number. Pull back by 20 to 30% and rebuild from there.
What actually counts as a set
A set that stops well short of failure barely counts toward this total. The volume research this range comes from generally used sets taken close to failure, one or two reps in reserve. Ten easy sets and ten hard sets are not the same ten sets; if you're not sure which you're doing, you're probably doing the easy kind.