What's the default resolution for minecraft texture packs?

I want to add a texture pack for Minecraft but I don't know what the default texture resolution is, as I don't want HD packs.

Should I look for texture packs that are 16x16 or 32x32 ?

The default texture resolution is 16x16.

Until Minecraft version 1.5, a client mod was required for higher resolutions.

The default resolution of Minecraft Vanilla (=unmodded) is 16x16 pixels. Any textures with higher resolution than 16x16 is called HD. Current version of Minecraft supports HD textures out of the box, just add the resource pack of your choice.

http://minecraft.gamepedia.com/Texture