The answer to 'what size GFCI outlet do I need' is that the size of the GFCI (Ground Fault Circuit Interrupter) outlet you need will depend on the electrical load and amperage requirements of the specific circuit it will be installed on. Generally, GFCI outlets come in 15-amp and 20-amp sizes, with the 20-amp being more common for household circuits.
The 15-amp GFCI is suitable for lighter-duty circuits like bathroom outlets, while the 20-amp GFCI is more appropriate for heavier-duty circuits that power kitchen countertop outlets, laundry rooms, or outdoor receptacles. It's important to match the GFCI outlet size to the circuit amperage to ensure proper function and safety.