Fertilizer Calculator
Convert a target nitrogen rate into how much fertilizer to spread, using the first N-P-K number on the bag, for any lawn or bed area. Calculates in your browser.
Product to apply
-
Show the math
The first N-P-K number is the percent nitrogen by weight, so:
product = (N rate × area ÷ 1,000) ÷ (N% ÷ 100)
A typical maintenance rate is about 1 lb of nitrogen per 1,000 sq ft per feeding. Don’t exceed label rates, over-application burns plants and runs off. All math runs locally in your browser.
What this does
A fertilizer calculator converts a target nitrogen rate into how much fertilizer to spread, using the first N-P-K number on the bag, for any lawn or bed area.
How to use it
- Enter the area to feed.
- Enter the target nitrogen rate.
- Enter the first N-P-K number.
- Read the pounds of fertilizer.
How it works
The first N-P-K number is the percent nitrogen by weight. Working from actual nitrogen lets you hit a consistent rate whatever the analysis.
fertilizer = N needed ÷ (N% ÷ 100)
Understanding your result
Working from actual nitrogen, rather than the bag weight, lets you hit a consistent rate whatever the analysis. Spreading more than the target risks burning foliage and polluting runoff, so weigh the amount rather than guessing, and split heavy rates into two lighter applications.
Example
For 1 lb of N per 1,000 sq ft from a 20-5-10 bag, spread 5 lb per 1,000 sq ft.
Sources & methodology
Last updated .
Frequently asked questions
What do the N-P-K numbers mean?
They are the percent by weight of nitrogen, phosphorus, and potassium. This tool uses the first number, nitrogen, to size the application.
What rate should I apply?
A typical maintenance rate is about 1 lb of actual nitrogen per 1,000 sq ft per feeding, but follow the product label and local guidance.
Why not just use the bag rate?
Bag rates assume one product. Working from actual nitrogen lets you compare fertilizers and hit a consistent rate whatever the analysis.
Is anything stored?
No. Everything is calculated locally in your browser.
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