Quick answer
For common plastic drywall anchors, the drill bit usually matches the anchor size printed on the package. Many light-duty anchors use 1/4 inch, while medium anchors often use 5/16 inch.
Light plastic anchors
Often 1/4 in
Medium plastic anchors
Often 5/16 in
Self-drilling anchors
Usually no pilot hole
Toggle anchors
Often 1/2 in or larger
Check the anchor package first
Drywall anchors are not standardized around one hole size. The safest quick rule is to use the drill size printed on the anchor package.
Snug is the goal
The anchor should push or tap into the hole with resistance. If it slides in loosely, the hole is oversized and the anchor will not hold its rated load.
Useful tools for this job
A mixed drywall anchor kit with printed drill sizes is the best match for this search because users often do not know which anchor they already have.
Frequently asked questions
Can I use a nail instead of a drill bit?
A nail can make a rough starter hole, but a drill bit gives a cleaner, rounder hole and a more predictable fit.