yep, It's safe
there are not many good rules of thumb when it comes to fungus, but with puffballs there is.
Larger than your fist, and pure white inside. Occasionally one will find an \"amanita egg\" IE an imature amanita, with the universal veil still encomapassing it. They are always smaller than your fist, and when you cut them open, the outline of an immature mushroom will be apparent. There are also another type of puffball, scleroderma species, they are usually refered to as earthballs. They are smaller than your fist and the endoperidium is dark (the inside) If you wanted to post a pick, i could probably tell you the species of your find. It could be calvata gigantea (the eastern giant puffball) calvata booniana(the western giant puffball) or calvata craniformis (which is widely distributed and has a sterile base, so t looks like it is on a pedestal) or maybe calvata bovista (also with a sterile base and low pyrimidal warts) all of which are edible.