Load regulation is defined as the amount output voltage changes in response to the load change, as a percentage. The load at the output changes due to several factors including changing load resistance in different circuit conditions. Load regulation is calculated as:
(Output voltage at no-load - Output voltage at full-load) / Output voltage at full load X 100%
For example, a voltage regulator has a 5 V output when there is no-load, i.e. load current = 0 A. During full-load condition, the load current is rated at 10 mA, as a result of that, the output voltage changes from 5 V to 4.95 V. The load regulation is determined as below:
The no-load output voltage = 5 V
The full-load output voltage = 4.95 V
The load regulation = (5 - 4.95) V / 5 V X 100 % = 1 %
Noted that no load condition indicates the output draws the minimum amount of load current while full load means the output draws maximum amount of current at the output.