Not off the top of my head,
There should be either a tag on the compressor, or a sticker on the firewall somewhere. If you go to a shop and have it evacuated they will put it on a machine that will put in the correct amount.
You definitely need to evacuate the system for at least 45 minute or so, if you left it open. Actually if you left the system open this whole time, you should just replace the receiver/dryer. The desicant will be saturated.
Good luck,
Scott