Yes, you can absolutely increase the size of your “butt” by increasing the size of the gluteus maximus muscles through proper resistance training. In addition, you will most likely find that the shape of the gluteal muscles also improves as the muscles become larger. People often describe the transformation from small glutes to larger glutes as going from a “flat butt” to a “round butt.”
To do this, you will need to target the gluteal region with exercises that promote extension of the hips at a load (weight) and volume to which you are unaccustomed. That is, you need to progressively overload the glutes with increases in weight and/or sets and repetitions so that the muscles are stimulated to increase in size (hypertrophy). Whichever repetition range you choose [low (1 to 5 repetitions); medium (6 to 12 repetitions); high (13 to 20 repetitions); or very high (21 to 50 repetitions)], your muscles will respond by growing larger as long as you push yourself toward muscular failure during each set. This is helpful because it doesn’t matter if you have access to a gym with a large selection of weights and machines or if you workout at home with limited access to load and equipment.
The following list of exercises promote gluteal work by emphasizing extension of the hips:
Dumbbell Step Up
Glute Activation Lunges
Single-leg Romanian Dead Lift
You can put together your own glute-challenging workout by selecting three or four of the exercises above per session. Perform four to six sets of between 6 to 20 repetitions per set (just remember to stop the set when your form starts to suffer). Start by performing these workouts twice a week and then, if you’re motivated and not chronically sore from muscle breakdown, eventually progress to up to four times per week. You could also consider gradually increasing the number of repetitions per set instead of increasing the frequency of workout days if that works better with your schedule.
Lastly, the number of inches a person gains in the gluteal region due to muscle hypertrophy is highly variable and depends on factors such as genetics, total physical activity per week, and nutritional intake. So, it is possible to gain 2 inches in hip circumference from gluteal hypertrophy, but the results will vary based on the individual. Also, keep in mind that if you become more physically active as a result of starting a new workout program, you could experience body-fat loss, which could shrink the hip circumference. However, performing an exercise program that targets the gluteals could potentially improve the shape of the area so that the number of inches might not be as important to you in the long run as the appearance of the glutes.