Stainless steel grate - made to measure

How do I calculate the price when buying a made-to-measure?

Multiply the width x depth (in the case of a circular grate, diameter x diameter) of the grate, then divide the result by 100 - you will then have the number of products you need to add to your basket to buy a grate to size with the thickness you want. 1dm2 of surface = 1pc of product

Example: you want to buy a grate with a diameter of 55cm.
The calculation should be as follows: 55 x 55 / 100 = 30,25.
This means that you should add 31 pieces of the product to your basket.