Table speed will vary depending on the atmospheric conditions and the table condition. The condition of the cushion rubbers, the cloth type and condition (both on the bed and on the cushions) have a large impact on the speed.
Different players prefer different conditions, usually because they are used to practising on a particular table. Playing in local leagues is a good way to improve your adaptability to different conditions.
Speed is generally measured in lengths of the table; that is, by throwing a ball as firmly as is sensible to the top cushion and counting how many times it travels up and down. A standard speed would be considered to be around 4 1/2 to 5 lengths (the ball ending up between the middle and top of the table when going towards the top cushion). 4 lengths would be considered as very slow and 6 lengths very fast.