What type of popper is it? The 50030178 model isn't one I'm familiar with.
For most of the small air poppers, such as the Presto Air poppers, fill the measuring cup lid with popcorn so that the popcorn is level with the top of the cup. Add this amount of popcorn to the popper. On those units, there is a fill line inside the popping chamber. Do not fill past the line. For these air poppers, if you want to have butter or margarine on the popcorn, add 3 tablespoons of the extra to the lid after you replace it on the popper.
For the Hamilton Beach Hot Oil Poppers, the manual for the 73300 is available here: http://www.hamiltonbeach.com/use-and-care/use-and-care.php
. Fill in the type of device and then the model. The amount of oil and popcorn will depend on how much you want to make. For a single serving, you need 2 T (tablespoons) of kernels and 1 - 1 1/2 t (teaspoon) of oil. For enough popcorn for a family, you should use 1/2 cup of kernels and 1T of oil. http://useandcares.hamiltonbeach.com/files/840190701.pdf
has a full chart of the amounts on page 6.
I hope this helps. Please add a comment with the brand of popper and I'll check for a specific chart for that unit.
(It's been a while since I used the air popper that I used to have.)