Fertilizer Rate Calculator
Convert a soil-test nutrient recommendation into fertilizer product, bags, cost, and co-applied N, P, and K. Use the rate from your soil test, then enter the bag grade.
For 5,000 sq ft needing 1 lb N per 1,000 sq ft from a 20-0-0 fertilizer, use about 25 lb of product, or 1 50 lb bag.
Fertilizer grade
Price
How to use it
- Enter the soil-test rate. Choose nitrogen, phosphate, or potash, then enter the target rate and its unit.
- Enter the area. Add the area to fertilize and choose square feet, acres, or hectares.
- Enter the fertilizer grade. Type the N, P, and K percentages from the bag label, plus price and bag weight if you want cost.
- Read the product rate. Use the result for total product, bags, cost, product rate per acre, and co-applied nutrients.
How this estimate works
The calculator converts the soil-test target to pounds per acre, converts the area to acres, then divides the target nutrient rate by the selected grade percentage. The same product rate is used to show the N, P, and K that are applied together.
Sources
Fertilizer grade and rate math follow UGA Cooperative Extension soil-test guidance and Penn State Extension fertilizer grade guidance. Local extension, soil lab, and fertilizer label instructions should override a calculator.
Fertilizer rate questions
How do I calculate fertilizer product from a soil-test rate?
Divide the target nutrient rate by the fertilizer grade as a decimal. For example, 1 lb of nitrogen per 1,000 sq ft from a 20 percent nitrogen product takes 5 lb of product per 1,000 sq ft.
What do the N, P, and K numbers on the bag mean?
They are the guaranteed percentages by weight: nitrogen, phosphate, and potash. A 20-0-0 product is 20 percent nitrogen, so every 50 lb bag contains about 10 lb of nitrogen.
Why does the calculator show co-applied nutrients?
A fertilizer chosen to meet one nutrient target can apply the others at the same time. If you meet nitrogen with a 10-10-10 product, the same product also applies phosphate and potash.
Can I use metric rates or hectares?
Yes. The calculator accepts kg per hectare, lb per acre, lb per 1,000 sq ft, and lb per 100 sq ft, then converts the math to a common per-acre basis.
Does this replace a soil test or fertilizer label?
No. Use your soil-test recommendation for the target rate, follow the fertilizer label, and check local extension guidance for timing and placement.