Somebody here will know the answer for this, I think. Are the cleats on cycling shoes a standard size? Are they all the same width, height, and depth? Thanks heaps.
Nope. Pretty much every brand is a little different. They're basically all made to fit either a road shoe or a mountain shoe though. Road shoes usually have a three bolt pattern, in a triangle pattern. Mountain cleats have a two bolt pattern. Most pedal manufacturers use their own cleat, so if you know the pedal brand, you can get a cleat to match.
cleats differ widely by the brand & type of pedal the click in to. they can be radically different.
there are 2 main categories: "road" and "mountain", which can be used on either type of bike, but must be used on the corresponding type of shoes - ie. you can't put cleats for "road" pedals on a "mountain" shoe.
I have used, slots (with toe-clip) PSD and LOK all on the same Sidi "road" shoe. I've also used PSD on my "mountain" shoes. You need to match the clip to the pedal and I'm reasonably sure that "most" shoes will work with the exception that the larger LOK cleaty thing probably will not fit on a "mountain" shoe. Since I ride in Chicago, "road" shoes make it very difficult if you need to walk, at all. I use a touring/mountain shoe for everything because of it's adaptability.
Just my $0.02, things may be different for you.