No, all microwave bulbs are not the same size, although there are some common sizes.
While microwave light bulb sizes are fairly standard, you'll find some variations. Some microwaves use 15-watt, tube-shaped bulbs, indicating size differences. Furthermore, the type of installation, particularly for under-microwave bulbs, can require additional effort and potentially a different bulb style or size. So, while many microwave bulbs may appear similar, it's essential to check your microwave's specific requirements to ensure you get the correct size and wattage.
