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 basically 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.
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 contact 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.
Want to know what your lawn needs and when to apply it?
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