How do you calculate the take off speeds in Flight Simulator 2004

each aircraft lists the takeoff speed in their specs

When you select your aircraft in the facts it should say what the take off speed is and how much runway it needs.

As a level 3 you should understand the ideas behind using the proper category for questions by now. Flight Simulator is a computer game, so questions about it belong in the ''GAMES'' section. This section is for questions about real aircraft, not pretend ones from a computer game.