Mosaic portable boards, used for displaying mosaic tile samples, typically come in various standard sizes to accommodate different collections and preferences. Common sizes for mosaic portable boards might include:

1. **12 x 12 inches (30 x 30 cm):** A compact size suitable for displaying smaller mosaic tile samples or creating portable displays for easy showcasing.

2. **18 x 18 inches (45 x 45 cm):** A slightly larger size that offers more space for displaying medium-sized mosaic tile samples with enough detail.

3. **24 x 24 inches (60 x 60 cm):** A larger board size that accommodates a wider range of mosaic tile samples, providing ample space for showcasing various designs and patterns.

4. **Custom Sizes:** Depending on specific needs, there might be custom sizes available, allowing for flexibility in creating mosaic portable boards tailored to unique preferences or showroom requirements.

These sizes serve as common dimensions, but variations can exist based on manufacturer specifications, client preferences, or the type of mosaic tile being displayed. The aim is to provide enough space on the board to effectively showcase the mosaic tile samples while maintaining portability and ease of use for display purposes.