A tire's load rating is given in the service description found on the tire's sidewall. The load rating is a number from 0 to 150 followed by a letter. The higher the number, the higher the load rating. The numbers can be interpreted through a tire load chart.
Looking at your tire's side rim, there should be a number sequence following the format P195/60R15 87S. This is the tire's size classification. The last three digits of this code are the tire's service description and give the load and speed ratings. In this case, the tire has a load rating of 87 and a speed rating of S.
A load rating gives the maximum amount of weight a tire is rated to carry when fully inflated. Remember that you must multiply this number by four for a four-wheeled vehicle. Standard tire loads for commercial vehicles are between 70 and 110.
Tire load ratings are exponential, meaning that higher load ratings correspond to higher and higher weights. For example, a tire load rating of 10 means that a tire is rated to carry 132 pounds, whereas a tire load rating of 100 corresponds to 1764 pounds, which is much more than 10 multiplied by 132.