Hi there, I'm a little rusty, however maybe I can help.

Although Alexander had upwards of 32,000 infantry, and about 5,000 cavalry, it is important to recognise that these troops, although falling under the overall hegemonic direction of Macedon, were made up of a variety of different peoples.

... made for the Hellespont with a force composed of not much more than 30,000 infantry, including light troops and archers, and over 5,000 cavalry. Arrian, Anabasis Book 1.

Arrian would go on to detail the composition of these forces

Command of the right had already been given to Philotas, Parmenio’s son, with the Companion cavalry, the archers, and the Agriane spearmen; Amyntas, son of Arrabaeus, was attached to him with the lancers, the Paeonians, and Socrates’ squadron. On the left of these divisions were the Guards’ battalions, commanded by Parmenio’s son, Nicanor; next came the infantry battalions of Perdiccas, son of Orontes, of Coenus, son of Polemocrates, of Amyntas, son of Andromenes, in that order: finally the troops under Amyntas’ son, Philip. The advance position of the left wing was held by the Thessalian cavalry under Calas, son of Harpalus, and these were supported – in the following order – by the allied cavalry under Philip, son of Menelaus, and the Thracians under Agathon. Immediately on their right was infantry – the battalions of Craterus, Meleager, and Philip, extending to the centre of the army as a whole.

In here are Greeks, Paeonians, and the elite Agrianeian Spearmen (well worth a bit of a look at them, they tend to be some guys who really get stuff done). Not to mention a few others.

Diodorus Siculus goes in to a bit more detail on troop composition (XVII.7.3-6)

3.... There were found to be, of infantry, twelve thousand Macedonians, seven thousand allies, and five thousand mercenaries, all of whom were under the command of Parmenion. 4. Odrysians, Triballians, and Illyrians accompanied him to the number of seven thousand; and of archers and the so‑called Agrianians one thousand, making up a total of thirty-two thousand foot soldiers. Of cavalry there were eighteen hundred Macedonians, commanded by Philotas son of Parmenion; eighteen hundred Thessalians, commanded by Callas son of Harpalus; six hundred from the rest of Greece under the command of Erigyius; and nine hundred Thracian and Paeonian scouts with Cassander in command, making a total of forty-five hundred cavalry. These were the men who crossed with Alexander to Asia. 5. The soldiers who were left behind in Europe under the command of Antipater numbered twelve thousand foot and fifteen hundred horse.

It could be, that, including for the Macedonian cavalry, there really were only c.18,000 Macedonians at the Battle of the Granicus. However, if that is the estimate of Alexander's combined deployed force for the battle it appears to be somewhat low, even given variables and exaggerations.