Lawn Fertilizer Calculator

Use this fertilizer calculator to determine how much fertilizer is needed to cover your lawn. Once you have purchased your fertilizer, we need to determine how much Nitrogen you need per 1,000 sq feet of lawn.

Every bag of lawn fertilizer has a (N) Nitrogen, (P) Phosphorus and (K) Potassium or N-P-K ratio on it. To manually calculate the amount of fertilizer needed, you need to calculate 1 – 1.5 lbs of Nitrogen per 1,000 square feet of lawn.


You have a 5,000 sq ft lawn and have just bought a fertilizer bag that is 20 lbs and has a ratio of 12-4-8. (that’s 12% nitrogen, 4% Phosphorus and 8% Potassium).

Multiply 20 lbs X 0.12 = 2.4 lbs of Nitrogen in the bag.

How many lbs/ bags?

You will need to apply 1.5 lb of Nitrogen per 1,000 sq ft of lawn. 

5,000 sq ft / 1000 = 5
5 / 2.4 lbs = 2.08

You will need 2 x 20 lb bags of 12- 4- 8 Fertilizer

General Fertilizer Calculator

If you are looking to buy some general purpose Scotts® Turf Builder Fertilizer, use the blow calculator to tell you how much you need to buy and spread. 

Pro Lawn Fertilizer Calculator

If you would like to go a little deeper and add the specific N-P-K ratios of your preferred fertilizer, we can tell you how much to buy and how to spread it. 

I want to cover
At a rate of Lbs of Nitrogen per 1,000 sq ft.
My Fertilizer's NPK ratio is - -
Spread a total of lbs of fertilizer over square feet.
That is a rate of lbs of fertilizer per 1,000 sq ft.
That works out to be 0 lbs of (N) Nitrogen, 0 lbs of (P) Phosphorus and 0 lbs of (K) Potassium per 1,000 sq ft.

To determine how much fertilizer to apply to your lawn

  • Measure the area of your lawn in square feet. Measure your lawn with a tape measure or use an online tool such as the Google Area Calculator (the link opens in a new window).
  • Determine the recommended rate of Nitrogen for your lawn. Nitrogen recommendations are usually given in lbs/1000 sq. ft. and made for the grass type being grown. There are some general recommendations in this website’s ‘grass types’ section. I also recommend checking your state’s extension service for nitrogen fertilizer rates. Please get in touch with me if you need help determining an appropriate nitrogen fertilizer rate. Phosphorus, potassium, and micronutrient recommendations are based on soil tests.
  • Choose the fertilizer product – You want to look for the fertilizer analysis on the label. The Fertilizer Analysis (N-P-K) is the three numbers on the label, and it indicates the percent by weight of nitrogen, phosphate (P2O5), and potash (K2O) in the fertilizer. This information is required to be on every fertilizer label.

One way to compare fertilizer products is the cost per pound of Nitrogen. Use this fertilizer calculator to determine the cost per pound of nitrogen in a bag of fertilizer.

Read more about choosing the best lawn fertilizer.

Best Fertilizers for Lawn

Let the turfgrass experts on Sunday take care of the technical stuff.

Have you heard about the Sunday Smart Lawn Plan? It’s simple, do-it-yourself natural lawn care customized to your soil, climate, and lawn. Delivered to you right when you need it. You apply the nutrient packets with the included hose-end sprayer…simple, professional results!

Sunday’s plant and soil nutrient products are from food waste, seaweed, and molasses. The natural additives stimulate plant growth and activate soil life.

This is Super Environmentally Friendly lawn care!

When to apply fertilizers?

The best time to fertilize your lawn varies based on your grass type and climate. Generally, we recommend fertilizing during the peak growing season: fall for cool-season grasses and spring for warm-season grasses.

Consider factors such as grass type, climate, soil conditions, and fertilizer type to determine the most effective timing for your lawn fertilization. 

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Lawns are good for the environment, our health and our homes. There are several benefits of healthy lawns that are often overlooked.

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