How fast is the universe expanding per second?
Space itself is pulling apart, expanding at a rate of 74.3 ±2.1 kilometers per second per megaparsec
The most precise measurement ever made of the speed of the universe's expansion was made by NASA's Spitzer Space Telescope
With "per megaparsec" I mean
distance of one million parsecs or 1Mpc
Astronomers typically express the distances between neighbouring galaxies (such as Milky Way and Andromeda) and galaxy clusters in Mpc (megaparsecs). One Mpc is about 3 million light years. (3.08567758 × 1022 meters)
Space is also expanding faster with time.
Expansion from Big Bang
How to calculate parsec - see more at https://en.wikipedia.org/wiki/Parsec