How many mines are in Expert Minesweeper?

Expert Minesweeper has 99 mines on a 30x16 grid. That is 480 cells in total, so the mine density is 20.6% - roughly one cell in five.

Mine counts on every standard board

These three configurations have been standard since the original Windows release and are what every leaderboard and world record refers to.

Why 99 and not 100

There is no deep reason - 99 is simply what Microsoft chose, and it stuck because records and rankings would be meaningless if the number moved. It has the small side effect that the mine counter never needs a fourth digit.

Why density matters more than the raw count

A board with 99 mines spread over 2,000 cells would be gentle. The same 99 packed into 480 is what makes Expert hard: at 20.6% you meet far more 3s, 4s and 5s, edges get crowded, and genuine 50/50 positions appear often enough to end otherwise perfect runs. Below about 12% boards largely open themselves; above 25% they stop being solvable by logic at all.

You can set any count you like on a custom board, or play No-Guessing mode to keep Expert density without the forced coin flips.