The standard: 2.5 by 3.5 inches
A standard trading card measures 2.5 inches wide by 3.5 inches tall — roughly 6.35 by 8.89 centimeters. This has been the common size for decades, and it is what almost everyone pictures when they think of a trading card.
Sports cards, Magic: The Gathering, and most modern collectible card games all use it. It is the default for a reason: it fits the hand, the page, and the entire ecosystem of accessories built around it.
Why the size matters for custom cards
When a custom card is printed at the true 2.5 by 3.5 inch standard, it drops straight into the existing world of card accessories — penny sleeves, top loaders, magnetic cases, binder pages, and display frames all assume that size.
A card printed at an odd size looks off next to real cards and will not fit standard protection. Printing to the standard is part of what makes a custom card feel legitimate.
How it affects your photo
The 2.5 by 3.5 ratio is slightly taller than it is wide — a portrait orientation. That is worth keeping in mind when you pick a photo.
A photo with some room around the subject crops cleanly into a card. A very wide landscape shot has to lose a lot of its edges to fit. You do not need to crop it yourself, but choosing a photo that suits a portrait frame gives the best result.
Oversized formats
Not every custom product sticks to the standard. Oversized formats — like a MEGA card poster — blow the card design up to wall-display size for a bedroom or locker.
Those are made to be shown off on a wall, not sleeved and collected. The 2.5 by 3.5 standard is for cards you hold, trade, and store; oversized formats are for display.