Hello searchinggal,
The 30" size refers to the cooktop itself, while the required cutout is smaller about 28 ½" to 28 ⁷⁄₈" wide. If your opening is over 30", the cooktop can still sit on top, but small gaps may be visible.
For the best fit and proper installation, we strongly suggest having a professional installer to handle the setup, especially if adjustments are needed.
You can explore the full guide here:
Samsung cooktop installation manual:
https://downloadcenter.samsung.com/content/EM/202412/20241202133624714/DG68-01666A-00_IM_NZ30FG5332RKAA_EN-MES-CFR_241126.pdf
Samsung values your business.
Rachel
Samsung Care