Quick answer
Toggle bolts usually need a hole large enough for the folded wings to pass through. Many common toggle bolts need a 1/2 inch hole, but the package size is the final authority.
Common hole size
Often 1/2 in
Rule
Hole must fit folded wings
Wall type
Drywall or hollow wall
Important
Do not oversize more than needed
Why toggle bolts need larger holes
Unlike plastic anchors, toggle bolts have wings that fold, pass through the wall, and open behind the surface.
How to test the hole size
Fold the toggle wings against the bolt and compare them to the bit. The hole only needs to be large enough for that folded shape to pass through.
Useful tools for this job
A toggle bolt assortment is useful when you are hanging shelves, mirrors, brackets, or other wall-mounted items on hollow drywall.
Frequently asked questions
Can I reuse a toggle bolt hole?
Usually not cleanly. Once removed, the toggle drops behind the wall, and the old hole may be too worn for a reliable reinstall.