What is the argon percentage in Earth's atmosphere?

The percentage of Argon in the atmosphere is 0.93% in volume.
(0.934 to be more accurate-pip)
The atmosphere is 0.934% argon by volume, so, a lot of argon.

The earth's atmosphere has a volume of about 3x1024 m3, which means that there are about 2.8x1022 m3 (5x1012 mi3) of argon in the atmosphere. The density of argon is about 1.77 kg/m3 so there are about 1.58 kg of argon in the atmosphere.