The general rule of thumb
Roughly 3-5 sets of 6-15 reps per exercise, close to muscular failure, works well for most people's muscle and strength goals — the exact number matters far less than showing up and applying effort consistently.
Lower reps, heavier weight (roughly 3-6 reps)
Better suited if pure strength is the primary goal — think powerlifting-style training. Builds strength efficiently but muscle growth is a bit slower per session compared to moderate rep ranges.
Moderate reps (roughly 8-12)
The classic 'hypertrophy' range — a good balance of strength and muscle growth for most general fitness goals, and probably the best default if you're not chasing a specific competitive outcome.
Higher reps (15+)
Still builds muscle effectively if taken close to failure, and tends to be easier on joints — a solid option for people managing an old injury or preferring lighter loads.
The honest bottom line
Weekly volume (total hard sets per muscle group) matters more than the specific rep range chosen. Roughly 10-20 hard sets per muscle group per week is a reasonable target for most people.