To get the right proportions, you want to get something that is close to a multiple of 3-1-1.8, so something like 6-2-4 or 10-3-6 would both be a little off, but close to what you want. If you can't get very close, remember which numbers were too high and get a fertilizer with those numbers lower next time to even it out.

To calculate how many pounds of fertilizer you need to get 1 lb/1000 sq ft, divide the number of sq ft you have by the first number on the fertilizer bag, then divide the result by 10.

For example, if you have 3000 sq ft of lawn, and find a fertilizer that is 6-2-4, you'd divide 3000 by 6 to get 500. 500 divided by 10 gives you 50, so you'd need 50 lbs of fertilizer.

If you had something like 10-3-6, you'd divide 3000/10 to get 300, then divide that by 10 to get 30 lbs of fertilizer needed.

If you have some odd number of sq ft or first number on the bag and it doesn't divide evenly, just try to get close to it. For example, with the 3k sq ft lawn, if the fertilizer is something like 21-7-15, you'd divide 3000/21 to get 142.857 . . . then divide by 10 to get 14.2 . . ., so you'd need a little more than 14 lbs. If it comes in 15 lb bags, that's close enough. If it comes in 20 lb bags, you probably want to leave about 1/4 of the bag.

No mystery here, you need 3 applications per year of a 3-1-2 ratio fertlizer which is a very common mix of 15-5-10. That translate to 6 to 7 pounds of product to every 1000/ft2

Thank you all...I make things more complicated in my head than they need to be I guess...:)