Nearly all the recipes posted here (except for Thai recipes), lemon and lime juice measurements are commonly ‘juice from 1/2 lemon’ or ‘juice from two limes’. For the readers, this works well if you have regular size lemons and limes where you live.
Here in Thailand, however, lemons are not that common, and limes are small, just a bit bigger than a golf ball. So for those viewers in Thailand that want to use a recipe that calls for the juice of a lime or lemon, use this as a guide, you can still use fresh limes and lemons, BUT measure the quantities.
These are average amounts:
1 lemon yields: 3 tablespoons of juice.
1 lime yields: 2 tablespoons of juice.