It really depends on what size/kind of rock you want to use.
Let's start with what I'll assume is the largest rock one would use in a rock garden - 3 to 5 in. River Rock:
1 Ton will cover about 80 sq. Ft. If you want to make sure there are no "holes"
1 to 3 in. River Rock:
1 Ton will cover about 100 sq. Ft. (no holes)
3/4 in. Rock:
1 Ton will cover about 150 sq. Feet at 1.5" deep... & 120 sq. Ft. At 2" deep
3/8 in. Rock - or crusher finds cover about the same as 3/4 in. Rock, but when using smaller rock, I like to cover at least 2" deep because there's more of a tendency for smaller rock to move around & settle, and you want to make sure you aren't looking at the weed barrier in half a year.
Let's start with what I'll assume is the largest rock one would use in a rock garden - 3 to 5 in. River Rock:
1 Ton will cover about 80 sq. Ft. If you want to make sure there are no "holes"
1 to 3 in. River Rock:
1 Ton will cover about 100 sq. Ft. (no holes)
3/4 in. Rock:
1 Ton will cover about 150 sq. Feet at 1.5" deep... & 120 sq. Ft. At 2" deep
3/8 in. Rock - or crusher finds cover about the same as 3/4 in. Rock, but when using smaller rock, I like to cover at least 2" deep because there's more of a tendency for smaller rock to move around & settle, and you want to make sure you aren't looking at the weed barrier in half a year.