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.
Need to calculate liquid fertilizer? Try our new liquid nitrogen calculator!
Need to add your lawn’s square footage? Use our brand new lawn fertilizer calculator!
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:
- Nitrogen (N-P-K)
- Pounds (total weight of the bag)
- Square feet (amount of ft² covered in the bag)
Let’s use a Lesco Starter Fertilizer for example:
- N-P-K = 18-24-12 (Type “18” into the nitrogen calculator)
- 50 lbs. (Type “50″ into the nitrogen calculator)
- 12,500 ft² (Type “12500” into the nitrogen calculator)
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 Lesco 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 Lesco per 1,000 ft²
4 lbs. x 3,000 ft² = 12 lbs.
So in my example, I’d need 12 lbs. of Lesco 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 Lesco 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 Lesco Starter Fertilizer again:
- 18 / 100 = 0.18 (N)
- 0.18 * 50 (lbs. bag) = 9 lbs. of N per bag
- 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.
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.
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.