The Templar force counted
"By counting the number of dead and missing in a battle, the researchers established the number of figthers present in the Orient. This gives between 300 and 400 for each of the three orders, the Templars, Hospitallers and TeutonicKnights. That is not much in the eyes of the opinion of the time, given their wealth. But the knight is never alone. He is assisted by grooms and valets without whom he can not be effective in the field. In addition, the heavy cavalry needs light cavalry, that is to say, foot soldiers,archers and crossbowmen. At every few hundred knights one must therefore add a few thousand auxiliaries.
A more accurate estimate is made when the Templars were repatriated to France, following the loss of Saint-Jean d'Acre in 1291. That's even why they so concerned about the royal power. With fifteen thousand lances, the order is a more powerful army that the royal army, and always available. One understands better why this gave King Philip grey hair...."
In his "The New Knighthood" Malcom Barber states:
"By the late twelfth century and during most of the thirteenth century the Order probably had about 6oo knights and 2,000 sergeants on active service in the east.... During the thirteenth century the Order may have had as many as 7,000 knights, sergeants and serving brothers, and priests, while its associate members, pensioners, officials, and subjects numbered many times that figure. .... By about 1300 it had built a network of at least 870 castles, preceptories, and subsidiary houses, examples of which could be found in almost every country in western Christendom. The extent of the Templar empire can be gauged from the fact that in 1318 pensions were being paid to former Templars in twenty-four French dioceses, as well as in York, London, Canterbury, Dublin, Tournai, Liège, Camin, Cologne, Magdeburg, Mainz, Castello, Asti, Milan, Bologna, Perugia, Naples, and Trani, in Nicosia in Cyprus, and in the kingdoms of Aragon and Mallorca. In turn this network sustained fighting forces for the holy war in Palestine, Syria, Cyprus, and Iberia, together with some of the most formidable and impressive casties ever built."
Source text is this paper (in French; translated bij TN);illustration source