I usually go a 1/2 to full size up in Adidas depending on the model. I have found from trying on Nike sneakers I can wear my true size or 1/2 size up depending on the model. Sometimes within the same model I don't fit into identical sneakers. My guess...different plants, different standards.
Ex-Coach: U of Delaware & Drew U. Pro Kennex Ki-5(R) & Gamma RZR 98 (L)
Dunlop Black Widow 17 (63lb) Babolat N.Vy 16 (64lb) USTA 4.5.