Nitrogen Fertilizer Calculator

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Written By: Mark Marino

a Massachusetts Core Applicator License holder and owner/operator of Lawn Phix,

Updated on


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Trying to figure out how much nitrogen is in that bag of granular fertilizer? Or how much many pounds of N you’re putting down per 1,000 ft²? Use our Nitrogen Calculator below to quickly get accurate results.


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Nitrogen is needed

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How Do I Calculate the Total Amount of Nitrogen in Fertilizer?

There’s lots of numbers on the front and back of most lawn fertilizer bags that it can be quite confusing as to how much nitrogen (the “N” part of the “N-P-K” values) you’re throwing down per application. The three main numbers we need to calculate are:

  1. Nitrogen (N-P-K)
  2. Pounds (total weight of the bag)
  3. Square feet (amount of ft² covered in the bag)

Let’s use a Andersons Starter Fertilizer for example: 

  1. N-P-K = 18-24-12 (Type “18” into the nitrogen calculator)
  2. 50 lbs. (Type “50″ into the nitrogen calculator)
  3. 12,500 ft² (Type “12500” into the nitrogen calculator)
lesco granular fertilizer 052405 64 1000
The three (3) numbers we need to calculate

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Calculate Total Pounds of Fertilizer per 1,000 ft²

Now say your yard isn’t exactly 12,500 ft² which the bag completely covers for a full application. My yard for example is broken out into three sections, Zone 1-3: 3,000 ft², 3,000 ft², 9,000 ft². respectively. Taking Andersons Starter Fertilizer as the example again, how many pounds will I need for my Zone 1, which is 3,000 ft²?

Take the pounds of the fertilizer bag (50 lbs.) and divide that by the square foot coverage (12.5).

50 / 12.5 = 4 lbs. of fertilizer per 1,000 ft²
4 lbs. x 3,000 ft² = 12 lbs.

So in my example, I’d need 12 lbs. of Andersons Starter Fertilizer for my Zone 1. In the next section, we’ll break down how many pounds of nitrogen per 1,000 ft² we’re applying. 

Calculate the Total Pounds of Nitrogen per 1,000 ft²

Now that we have the total pounds of fertilizer per 1,000 ft², we can do some quick math to get how much Nitrogen we’re throwing down.

Multiply the pounds of fertilizer per 1,000 ft² by the Nitrogen amount (located on the bag) and divide by 100. In this case, my 3,000 ft² example needs 4 lbs. of fertilizer, and the “N” amount on the starter fertilizer bag is “18”.

4lbs * 18 / 100 = 0.72 lbs. N per 1,000 ft²

And using the formula above (or even easier, the nitrogen calculator) we’re getting 0.72 lbs. of N per 1,000 ft².

Nitrogen Calculations Summary

To summarize a quicker way – aside from using the nitrogen calculator – using Andersons Starter Fertilizer again:

  1. 18 / 100 = 0.18 (N)
  2. 0.18 * 50 (lbs. bag) = 9 lbs. of N per bag
  3. 9 lbs. / 12.5 (square foot coverage) = 0.72 lbs. of N per1,000 ft²

You’ve read how to calculate nitrogen and used the nitrogen calculator. Was it useful?

Please leave a comment below to let me know what you think. Feedback will help provide ideas to help enhance these calculators and possibly build some more in the near future. 

How much nitrogen fertilizer for lawns?

Generally 4 pounds per 1,000 square feet per calendar year is a good rule of thumb. However, this depends on many things. Before you begin a 4 pound per year lawn care program, first perform a soil test. Secondly, determine the type of lawn (cool season vs. warm season) and grass species. And remember with an increase in Nitrogen comes an increase in top-growth – so be prepared to mow.

When to apply nitrogen fertilizer to lawns?

For cool season lawns, for example in in New England, you can spoon feed nitrogen as frequently as every two weeks during the growing season, or as little as four times per year. For cool season lawns, Lawn Phix recommends approximately six applications per year – skipping the hot summer months to prevent burning and over-stressing.

What are the best organic nitrogen fertilizers?

Lawn Phix top picks:
Milorganite 6-4-0
Holganix BlueSky 21-0-0 and 2-10-20
Jonathan Green 8-0-1

What are the best synthetic nitrogen fertilizers?

Lawn Phix top picks:
Lesco Starter Fertilizer 18-24-12
Jonathan Green Winter Survival 10-0-20
Scotts Green Max

Author's Note: this piece has been updated for accuracy since its first publication on
Photo of author
Author: Mark Marino
My name is Mark Marino, and I am the founder, owner, and operator of Lawn Phix. With a passion for lawn care and turf nutrition for over a decade, I've dedicated countless hours to correcting soil and perfecting lawns. Today, my expertise, backed by formal courses at UMass Extension Pesticide Education, allows me to offer top-tier lawn care services and advice. I am a fully licensed and insured lawn care applicator in Massachusetts, specializing in comprehensive turf nutrition, weed control, and lawn pest control. My license number is AL-0053865. Contact me at [email protected] or +1 (508) 500-8402.

4 thoughts on “Nitrogen Fertilizer Calculator”

  1. if your soil has only 12 parts per million of nitrogen and you need to bring nitrogen up to 51 -75 par per million , how much nitrogen would I need per 1000 sg feet? do I need to apply nitrogen every year? thanks


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