Loading Ratio or DC to AC ratio of an inverter is the ratio of Rated Array Power (DC kWp) to Rated Inverter Output (AC VA). This can be expressed as a percentage value.
For example, if array output of 55kWp DC were connected to a 50kW inverter, the Loading Ratio would be:
(55kWp / 50kW) x 100= 110%.
One can find the Rated Array Power (DC kWp) & Rated Inverter Output (AC VA) of an inverter on the datasheet provided by the inverter manufacturer.