How do i know if i have a foot ulcer or callous?

Very different: A callous is simply built up dead skin. An ulcer is a hole in your skin. The latter is serious and a podiatrist should be consulted.

See a doctor: Most of the time a callous presents as hard thick skin. But I have seen ulcers under the callous so you should see a podiatrist to determine.

If unsure: I would see a podiatrist. They can yell the difference and better yet , they can treat it.