Calculating the appropriate rates for your fertilizer application can be confusing for those who don't do it regularly. Here are some helpful formulas and related information that can help get your acre squared away.

How to find the actual amount of a nutrient in a 50 lb. bag of fertilizer.

Ever wonder exactly how many pounds of a given nutrient are in one bag of fertilizer? While the all the numbers on the front of the bag don't always look like they all add up they all serve a very specific purpose. Using them you can easily calculate exactly how many pounds of a given nutrient are in a bag.

The three primary numbers listed on any fertilizer bag are listed as the percentage of the total weight of the bag and are always listed in the order of Nitrogen (N), then Phosphorous (P), and finally Potassium (K).

To find the actual amount by weight of these nutrients you just have to do some simple math.

  1. Convert the nutrients number by dividing by 100.
  2. Take that result and multiply by the bag weight, in this case 50 lbs. 

For example, let's use a blend of 20-6-16 is 20% Nitrogen, 6% Phosphorous, and 16% Potassium. Our 20-6-16; 20 divided by 100 gives us .2. Taking that result of .2 and multiplying it by 50 gives us 10. That means there is 10 pounds of Nitrogen in this particular blend. The same principle can be used for all the other nutrients in the blend.


How to find the number of bags needed for a desired application rate.

So, you want to fertilize your lawn. Great! After speaking with your Spring Valley dealer you find that perfect blend for your application. Now all you need to do is place the order. But how many bags are you going to need to cover your lawn at the recommended application rate?

To do the calculation you first need two pieces of information.The first is the target application rate, for example .75 lbs. of N/ 1,000 sq. ft. The second is the total area you will be applying the fertilizer to, for example: 40,000 sq. ft. Using this information you can find the total pounds of N you need to cover your lawn by multiplying your application rate by the number of square feet, then divide by 1,000.

So in our example: .75 x 40,000 = 30,000. 30,000 divided by 1,000 yields the number of pounds of nitrogen needed, in this case 30. So now we know how many pounds of nitrogen we need to cover our 40,000 sq. ft. lawn, now we just need to figure out how many bags of fertilizer we need to give us our 30 pounds of N. To do this just take your total nitrogen needs (30 in our example) and divide it by the amount of nitrogen in each bag. Using our example from above (How to find the actual amount of a nutrient section) of 10 lbs. N per bag we then are left with the calculation 30/10 which gives us an answer of 3 bags needed to apply .75 lbs. N on 40,000 sq. ft.

Common Units and Conversions

There are many different ways to measure a given space, most of which can end up very confusing. To help unravel some of the confusion here are some of the common units of measure and abbreviations used in the fertilizer application world along with a converter to aid in getting your units right.

N = Nitrogen
P = Phosphorus
K = Potassium
M = 1,000 sq. ft.
1 acre = 43,560 sq. ft.

Common Application rates:
.25# N per 1,1000 sq. ft (.25#N/M)
.50# N per 1,1000 sq. ft (.50#N/M)
.75# N per 1,1000 sq. ft (.75#N/M)
1.0# N per 1,1000 sq. ft (1.0#N/M)


Athletic Field Sizes

Golf Course

Green  4,000-7,000 sq. ft.  
Tee  3,000-8,000 sq. ft.  
Fairway  130,000-260,000 sq. ft  3-6 acres
Rough  87,000-130,000 sq. ft.  2-3 acres

Football Field

Field (160 x 360 ft.)  57,600 sq. ft.  1-1/3 acres

Baseball Diamond

Infield Area  8,100 sq. ft.  
Home plate to left field  300-360 ft.  
Home plate to center field  360-410 ft.  
Home plate to right field  300-360 ft.  
Mound to home plate  60 ft. 6 in.  
Home plate to first base  90 ft.  
Home plate to second base  127 ft. 3-3/8 in.  
Home plate to third base  90 ft.  

Tennis Court

Regulation (78 x 36 ft.)  2,808 sq. ft.  
Full (120 x 60 ft.)  7,200 sq. ft.  

Soccer Pitch

Small (195 x 330 ft.)  64,350 sq. ft.  1-1/2 acre
Large (225 x 330 ft.)  74,250 sq. ft.  1-3/4 acre

Rugby Pitch

328 x 226 ft. 74,128 sq. ft.  1-3/4 acre

Hockey Pitch

Small (301 x 164 ft.)  46,364 sq. ft.  1-1/8 acre
Large (300 x 180 ft.)  54,000 sq. ft.  1-1/4 acre

Cricket Square

90 x 90 ft.  8,100 sq. ft.  


75 x 40 ft.  3,000 sq. ft.  

Lawn Bowling

Minimum 110 x 100 ft.  12,100 sq. ft.  
Maximum 125 x 110 ft.  13,750 sq. ft.  


30 x 60 ft.  1,800 sq. ft.