You have several options: high, low, diagonal, none, none visible, and baldric. Often more than one belt is worn.
High: usually fairly narrow and worn just below the ribs and just below the breastplate if one is evident.
Low: worn very low on the hips. If a fauld is worn, the low belt should sit approximately on the bottom lame. Walter von Hohenklingen, 1386 wears both a high and low belt.
A horizontal belt worn low on the hips may not be a good way to hold up a heavy sword, so it's not uncommon to see a diagonal, often fairly narrow belt instead of or in addition to the low one. Sir Humphrey Littlebury wears both. (I suspect from his gauntlets that he may be somewhat earlier than 1365.) Lord John de Montacute also has a second belt, in this case neatly rolled around his scabbard.
Even when no diagonal belt is visible, it isn't safe to assume that a low belt is supporting the sword. Swords and daggers can be attached directly to body armor. In Altichiero's Execution of St. George the soldier directly behind the saint has both sword and dagger attached directly to his blue brigandine.
In some cases, a belt may be worn, but beneath the jupon or coat armor. Perhaps that's what's happening in this illumination of Richard II meeting Northumberland
Du Guesclin's effigy shows a baldric worn with a high belt. A baldric is also worn by one of the figures on the right side of a miniature of Siege of Melun
The belts of the knightly elite shown on effigies were often broad and almost always richly decorated: 1-2.25" or more wide, compared to diagonal belts that might be .75-1" wide. These low belts are usually made either of linked metal plaques, or of large mounts densely covering a leather or textile belt for a similar effect. Even when large, these mounts were not necessarily very massive. Many large mounts preserved in the Museum of London were stamped out of metal sheet. Three circular armorial mounts, about 2 3/8" in diameter, also in the Museum of London, of silvered copper alloy with armorial designs of enamel or niello weigh between 43.5 and 57.5 grams. Of composite construction, the central armorial rondel is made of engraved sheet, and surrounded by a ring that shows turning marks. For this class, high and diagonal belts as well as baldrics were often lavishly decorated with mounts.
During this period, most fully armored men-at-arms were not knights, but squires and gentlemen. While an ordinary squire was less wealthy than a knight, anyone that could afford full armor and a warhorse was not poor. Their belts were not as richly decorated as a knight's, but contemporary illuminations still show belts on most men-at-arms richly decorated with mounts. Men of this rank could afford mounts of copper alloy or better