I would say a minimum of 24" above the sink, but I would go at least 27" and do something like this.


Here are more pictures to look at.

https://www.houzz.com/photos/cabinet-above-sink-phbr0lbl-bl~l_719

I agree with Fred, 18" is not enough room over the sink. Especially for your height, look at shallower than standard 12" deep cabinets, open shelves, or a combination that best covers your needs.

Thank you. How about the width of the cabinet over the sink? If I do a 33" sink cabinet, should I do a 33" upper over the sink or should I do a 36" or 39" or 42" or 45". Please remember my galley kitchen is 7 X 13. I want to order the cabinets today. Thanks again for your help!

It sort of depends on the cabinet layout design. If you have a 33" base, you would normally go to a 33", 39", or 45" upper to line up the rest of the cabinets. Unless you want open side shelves, I would probably go with 39"?