How do I select the logo size on a product?

Short answer: In the product configuration, click the logo and then select a version. The version sets both the printed size and the price of the marking.

How it works

When you upload a logo, the system automatically calculates several versions of it — simply several sizes. There are two reasons for this:

the cost of the marking depends on the rectangular surface of the logo;
some placements have a maximum size (on a cap, the logo cannot be taller than 5 cm or wider than 9.5 cm).

Steps

On the “Shops” page, open a draft of the shop — a live shop cannot be edited directly (orange “Modify the shop (create a draft)” button).
In a collection, click the product to open its configuration.
Opposite the placement you want, click the logo thumbnail to switch it on.
Just under that thumbnail, open the drop-down menu and select the version. Each line of the menu carries the version name followed by its price — that is where you see straight away what a size costs.
Save.

The price displayed to the right of the placement updates as soon as you change version.

The product needs at least one non-optional logo: that is the one that sets the product price.

On Kids / Junior products, make sure you leave the Junior version in place, especially on the heart placement. See What is the Junior version for.

The menu only offers the versions that are compatible with the placement. On a cap, for example, versions that are too large do not appear at all. If the selected version exceeds the maximum width or height of the placement, a warning is displayed and the logo will be reduced automatically when printed.

Going further

How big will my logo be — the real size, in millimeters.
What is a logo version and why are there several — how versions work.
Why does the price change when I modify the logo dimensions
How do I change the size of a logo version

You'll know it worked when: The product shows the version you wanted, and its price matches the rectangular surface of that version.