The next consideration when purchasing a new air compressor is, "How much PSI will I need?"
For the newbies, PSI is short for "pounds per square inch" and this is how most compressors in the US are rated. In Europe, you will see them measured in bars. PSI is all you need to worry about on this side of the Atlantic.
Most of the commonly used air tools require about 90 PSI to operate correctly. However, you will still need a compressor with a higher shut-off pressure. Most air compressors that you find at the local hardware giant are "single-stage" and shut off at 125 - 135 PSI. Don't let that fool you. You might think all you need is 90 psi, so that should work just fine. Generally, these light duty compressors shut off at 100 psi and don't forget about pressure loss in the line. The little light duty compressor will barely run an impact.It might be fine for light duty garage use, but if you really intend use your air tool, more is definitely better. Many industrial compressors are "two-stage," which means they build up to shut-off pressure in two stages. The first stage builds to about 90 PSI and the second stage builds to 175 PSI.