The cooktop size refers to the actual measurement of the appliance, while the cutout measurement is the minimum required space you need to be able to install the cooktop into your counter. The difference between these two measurements is typically 1/2" or less and should be taken into consideration when selecting a new cooktop for your kitchen.
Following these measurements and guidelines can help ensure that you select the right cooktop for your kitchen. With the proper size, installation and ventilation, you can enjoy cooking with your new cooktop for a long time.