Reading the code8M-1200-30 is a 8M belt with a 1200mm pitch length and a 30mm width. Some brands write it the other way round, such as 1200-8M-30 or 30-8M-1200, but the numbers mean the same thing.
Counting teethPitch length divided by 8mm gives the tooth count, so a 1200mm 8M belt has 150 teeth. If the code has worn off, count the teeth and multiply by 8 for the length.
HTD or Supertorque?Supertorque S8M belts have the same 8mm pitch but a different tooth shape. They need their own pulleys, so check the tooth profile before swapping.