Hi MR.
Thank you for reaching out regarding your Samsung - 30" Built-In Gas Cooktop with WiFi on the width and depth needed for the cutout. Regarding your concern, the cutout width would be 28 1/2" W and the depth would be 19 5/8" D.
I suggest you check this link for the full specs, features, and dimensions.
https://www.samsung.com/us/home-appliances/cooktops-and-hoods/gas-cooktops/30-gas-cooktop-2018-na30n6555tg-aa/#specs
Should you need more assistance, please feel free to get back to us via the following options:
1. Facebook Messenger: http://m.me/samsungsupport
2. Twitter: https://twitter.com/messages/compose?recipient_id=18768513
3. Samsung Community: https://us.community.samsung.com/t5/Samsung-Community/ct-p/us
Reference Ticket Number: 1144663433
Thank you for being a valued customer of Samsung. Have a great day.
^Camille