Quick summary of ideal rep range for your goals:

Strength with minimal gains in muscle mass.

1-5

Maximal strength and hypertrophy gains.

6-8

Hypertrophy with some strength gains/ Ideal for sustaining muscle mass during a fat loss phase.

9-12

Strength endurance gains and lower muscle mass gains.

13-20 reps

Beginning an exercise plan for the first time, the first variable we need to consider is how many repetitions are required for our specific goal.

If strength is our goal, because we are involved in sports that require us to gain strength, such as powerlifting or Olympic weightlifting then training the big lifts such as squats, Olympic lifts, overhead press, or deadlifts needs to be trained in the 1-5 rep range for maximal strength.

If our goal is to gain strength and muscle mass, because we are involved in contact sports that require the need of body armor to take a hit, then we need to aim for the 6-8 rep range.

When our goal is to pack on muscle mass, or we are starting a fat loss phase, ideally the 9-12 rep range is recommended. For a fat loss phase, when we are cutting back on calories, muscle mass is the first to go, therefore working in the 9-12 rep range forces our body to prioritize muscle over fat; which will burn fat to make up for the loss calories in our diet.

For strength endurance with lower muscle mass gain, targeting 13-20 reps is best.

Sticking to only 1 rep range for your specific goal will work for the first 6-8 weeks, however, in the long run alternating different rep ranges will be more effective. For example, programming lower reps into your hypertrophy phase will make you stronger to lift heavier weights in the 9-12 rep range—the heavier you lift, the more tension you apply to muscles over time will make them grow. For that reason, I recommend play with the rep ranges and find the one that works best for you and your goals.