You usually choose a hole to put something through it such as a component pin, a wire or a mounting screw. So hole diameter is to meet your specific requirements and is usually specified by the device datasheet, or onlien resources for clearance hole diameters for wires, screws etc. Allow an extra 36um on the diameter to allow for plating thickness on plated through holes. See: [https://easyeda.com/forum/topic/How-thick-is-the-through-plating-of-a-through-hole-pad-0690fda822f84520a9dbddc662fb8dcf](https://easyeda.com/forum/topic/How-thick-is-the-through-plating-of-a-through-hole-pad-0690fda822f84520a9dbddc662fb8dcf) for more. For thermal vias in pads etc. see: [https://easyeda.com/forum/topic/How-to-place-multiple-vias-in-a-PCB-footprint-a34cf68d58414138898a56de60abd8c1](https://easyeda.com/forum/topic/How-to-place-multiple-vias-in-a-PCB-footprint-a34cf68d58414138898a56de60abd8c1)

For vias, I always go for a via pad size of twice the drill size.  You choose the via drill size based on the current being carried through the via.  12/24mil is a farly common choice for logic, 25/50 for power (and use several of them)

Mike, Do you know of anywhere that gives any guidance on via diameter (filled or empty?) vs. current or temperature rise?

@andyfierman Unfortunately not as it's PCB manufacturer specific.  As I often put 10s of Amps through a board, I usually get a test board made and measure the voltage drops for various size holes.  But I always derate significantly from these measurements, something I learned from IC design where via repeatability is generally quite poor.