No, these are not three different sizes of the product. The description "Mixing bowl (26 cm, 3 l, 3 x)" means that it is a mixing bowl with the following properties:

- Diameter: 26 cm
- Volume: 3 litres
- Quantity: The product is supplied in a pack of 3 bowls.

So there is only one size, but the product is sold in a pack of three bowls.