According to Home Depot, the easiest way to determine the amperage of an electrical panel box is to look at the amp rating of the main breaker. The two are generally the same. However, if there are doubts, owners should look for other clues as to the amount of power supplied to the home.
Many service panels have an attached label indicating their amperage rating. Sometimes, the manufacturer affixes a label to the box prior to shipping to the supplier. Other times an electrical inspector attaches a label at the time of installation.
The electric meter often indicates an amperage rating. This is sometimes on the meter face and at other times on the meter body.
The size of conduit carrying the main service wire into the home offers an indication of the number of amps the line carries. The conduit is the pipe entering the home from the main service line, either from under the ground or overhead lines. A 1-inch conduit provides room for a 60-amp service; however, a 200-amp service requires a 2-inch conduit. Homeowners should beware that conduits are often oversized, making it possible that a 2-inch conduit only carries 60-amps of electricity, but a 1-inch conduit is a sure sign that the maximum service is 60-amps.