Sizes in a simple letter model are a choice of the size strategy you wish to use such as fixed width or fixed height. And a combination of maximum characters per line/maximum number of lines of text allowed for each size.
Make sure you add all your sizes before moving on to adding pricing.
How to add a size to your simple letter model customiser:
Navigate to the Sign Customiser admin on your store.
Click on "Customisers"
Click on the customiser you wish to edit
On the left-hand side menu click on "Sizes"
Click on "Add a new size"
On the edit size page form fill in all the required details about the size you want to add:
In the Label section, you have to add the name of the Size you want to add. (For example, small/big)
In the Description section, add a description of the Size you are adding. (For example, minimum 10cm and maximum 60cm)
Choose your Size Strategy, select either "Fixed Width" or "Fixed Height".
In the Minimum Text Characters section, add the minimum number of text characters for your sign. (For example, The minimum number of text characters for the entire sign. If kept blank, the default minimum is 3 characters. The user cannot add less than 3 characters per line)
In the Maximum Text Characters per line section, add the maximum text characters allowed per line. For example, The maximum number of text characters allowed per line e.g. 20 text characters per line. The user cannot add more than 20 characters per line)
In the Lines of text allowed section, add the number of lines for the text allowed. (The number of lines of text that is allowed for this size, 1,2,3)
In the Width (in centimetres) section, add the number of maximum widths for the size you are adding. (The maximum width for this size e.g. 60cm.
7. Once you have filled in all the details, click Save, in the bottom right corner.
Size Strategy
Fixed Width - Fix the width of the sign to a set size, e.g. 60cm, and the height of the sign will be dynamically calculated using the number of lines of text/shape of the font/width set.
Fixed Height - Fix the height of the line to a set size, e.g. 8cm per line, and the width will be dynamically sized according to the number of characters/shape of font/height.