The number of titans is equal to the earths population a titan can be any where from 4 to 75 meters or around 12 to 225 feet tall. (Most are between 5 and 15 meters tall)They heal and regrow body parts and can only be killed by destroying the napes of there neck. Steal is not durable enough to cut or hurt titans but other stronger marvel metals should be able to. Titans don't age.
The titans randomly appear all over the earth . On new years day 2014 around 6 am. No prep on either side and neither know of each others weaknesses