How small should touch triggers be at minimum?

Question

Is there a known minimum physical size for reliable touch select triggers, considering only selection (no long-press or drag). From personal experience, I would guess it to be about 5x5 mm (0.2x0.2 inch). Is there a canonical answer?

Context: I want to make my chess-like game board have as many cells as possible, but I still want users to be comfortable selecting cells, as it will be a frequent action.

Answer 1

There's a comprehensive question on UX about touchscreen button sizes. The recommended size depends highly on your game, but the minimum size is quoted as 9-12mm, about half an inch, and this is based on the size of fingers.

Keep in mind that this is a guideline, and the cost of ignoring it is that your users will tap the wrong thing on occasion.

Depending on your game, you may need to go bigger - sometimes much bigger - than this minimum guideline. Here are some factors that will affect accuracy:

• Do you need to tap quickly? Faster means less accurate
• Will players use their thumbs? Less accurate
• Is your demographic experienced gamers or younger? They may have above-average accuracy
• Will your touch zones be right next to each other or have gaps in between? Gaps make it easier to use

You may also decide to accept a certain amount of input errors, as long as you make it easy for your players to correct themselves. Consider:

• Allowing players to adjust their input after the initial tap
• Add a "confirm" step
• Add an "undo" function
• Add clear feedback during the input to show what the game thinks the input will be
• Reduce the impact of errors