What’s the smallest practical x86 board for a DIY handheld?

For a standard off-the-shelf motherboard, Mini-ITX is a common compact option. It’s still much larger than a handheld’s internals, though, and you’d need to account for the board, cooling, battery, controls, and display together.

If the target is genuinely handheld-sized, look at complete mini-PC or laptop hardware rather than a conventional desktop board. Those systems can use compact mobile components, but adapting them means working around their existing layout, cooling, and power connections.

Mini-STX is smaller than Mini-ITX, but it’s still a small desktop-board format, not a drop-in handheld solution. Check the board dimensions and connector placement before buying, since the overall assembly may end up much bigger than the board suggests.

A bare laptop motherboard or a compact mini-PC board may be closer to what you need. The tradeoff is that these are often designed for a specific chassis, so sourcing a compatible heatsink, power input, and display connection can be the hard part.