Purdue University has developed a simple yet informative fertilizer application calculator that just about anyone can understand and apply.

They recommend fertilization rates in pounds of nitrogen per thousand square feet or lbs N/1000 sq ft.
You can use our fertilizer calculator at
http://www.agry.purdue.edu/turf/fertcalc/Fertilization%20calc.html or you can use the handy instructions below.

If you chose to calculate it yourself, use the following two steps:
Step 1. Calculating the amount of fertilizer/1000 sq ft:
Desired rate in lbs N / 1000 sq ft ÷ % nutrient = Total fertilizer needed / 1000 sq ft

Step 2. Calculating the amount of fertilizer to treat the entire turf area:
Total fertilizer needed / 1000 sq ft X Area to be treated in sq ft = lbs fertilizer needed to treat the area

For example, how much fertilizer do you need to apply a 16-8-8 fertilizer at 0.75 lbs N/1000 sq ft to an 8000 sq ft lawn?
Step 1. Calculating the amount of 16-8-8/1000 sq ft:
0.75 lbs N / 1000 sq ft ÷ .16 N = 4.69 lbs 16-8-8 / 1000 sq ft

Step 2. Calculating the amount of 16-8-8 to treat the entire 8000 sq ft turf area:
4.69 lbs 16-8-8 / 1000 sq ft X 8000 sq ft = 37 lbs 16-8-8 needed to treat an 8000 sq ft lawn

You’ll need 37 pounds of 16-8-8 to treat the 8000 sq ft lawn at 0.75 lbs N/1000 sq ft. More information of choosing fertilizers, fertilization schedules, calibrating spreaders, and more can be found in AY-22: Fertilizing Established Lawns.