There are many kind of custody that are possible.  In Utah, there are legal custody and physical custody, with there being the combination possibilities of sole legal and physical custody residing with just one parent, joint legal custody but sole physical custody, joint legal and physical custody, and varieties of split custody (children divided between the two divorcing parents’ homes).
To begin with, it is a modern myth that a parent who has sole legal and physical custody of a child has all parental rights and the “noncustodial” parent has no parental rights.  Wrong answer.  For Utah policy on parent-time, see https://le.utah.gov/~code/TITLE30/htm/30_03_003200.htm.  Under Utah law, the minimum “parent-time” (no longer called visitation, because a noncustodial parent doesn’t just visit their child/ren, but parents them during the time they spend with the noncustodial parent), provides (generally) for the noncustodial parent-time to be every other weekend, every other holiday, 1/2 the winter vacationbreak and 4 weeks in the summer.  In Utah, for children 5 and older, see https://le.utah.gov/~code/TITLE30/htm/30_03_003500.htm.  In Utah, for children younger than 5, see https://le.utah.gov/~code/TITLE30/htm/30_03_003505.htm.  In Utah, for parents who live further than moving 150 miles or more from the residence specified in the Utah court’s decree, see https://le.utah.gov/~code/TITLE30/htm/30_03_003700.htm.  For Utah advisory guidelines suggested to govern all parent-time arrangements between parents (which are often adopted as the law of the case in divorce decrees and are no longer “advisory” but required), see https://le.utah.gov/~code/TITLE30/htm/30_03_003300.htm.
Physical custody has to do with where the child/ren live – their “primary residential placement.”  In other words, in which home does the child/ren primarily sleep?  Joint custody is where the child/ren have more of a time share between the two parents’ homes than that of a sole physical custody arrangement.  For Utah, see https://le.utah.gov/~code/TITLE30/htm/30_03_001001.htm
Legal custody has to do with parental decision-making regarding the decision, such as who has the right to make can i buy ativan in mexico? final decisions regarding the health, welfare, religion, and education of the child/ren.  It is assumed that the parent with whom the child is spending parent-time at any given time will make the day-to-day decisions for the child/ren.  A divorce decree will state if legal custody is sole or joint, and if joint, how those decisions will be made, to include what process will happen if the parents reach an impasse.  For Utah, see https://le.utah.gov/~code/TITLE30/htm/30_03_001003.htm, https://le.utah.gov/~code/TITLE30/htm/30_03_001007.htm, https://le.utah.gov/~code/TITLE30/htm/30_03_001009.htm and https://le.utah.gov/~code/TITLE30/htm/30_03_001001.htm.
As for determining custody, Utah law requires that the court look at the following:  “In determining parent-time rights of parents and visitation rights of grandparents and other members of the immediate family, the court shall consider
the best interest of the child.”  See https://le.utah.gov/~code/TITLE30/htm/30_03_000500.htm.  This is obviously very general, so the court will look at a variety of other rules and case law, beginning with the following factors:

(5)(A) the child’s preference;

(5)(B) the benefit of keeping siblings together;

(5)(C) the relative strength of the child’s bond with one or both of the prospective custodians;

(5)(D) the general interest in continuing previously determined custody arrangements where the child is happy and well adjusted;

(5)(E) factors relating to the prospective custodians’ character or status or their capacity or willingness to function as parents, including:

(5)(E)(i) moral character and emotional stability;

(5)(E)(ii) duration and depth of desire for custody;

(5)(E)(iii) ability to provide personal rather than surrogate care;

(5)(E)(iv) significant impairment of ability to function as a parent through drug abuse, excessive drinking or other causes;

(5)(E)(v) reasons for having relinquished custody in the past;

(5)(E)(vi) religious compatibility with the child;

(5)(E)(vii) kinship, including in extraordinary circumstances stepparent status;

(5)(E)(viii) financial condition; and

(5)(E)(ix) evidence of abuse of the subject child, another child, or spouse; and

(5)(F) any other factors deemed important by the evaluator, the parties, or the court.

See https://www.utcourts.gov/resources/rules/ucja/ch04/4-903.htm