Lawn Fertilizer Calculator: Pounds per 1,000 sq ft
How much fertilizer does my lawn need? Enter your lawn area, the pounds of nitrogen you want per 1,000 sq ft and the nitrogen percentage on the bag (the first number of the N-P-K grade). This page is for feeding an existing lawn; it does not size seed or sod.
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Formula
product per 1,000 sq ft = target N (lb) / (N% / 100)
total product = product per 1,000 sq ft x area / 1,000
bags = total product / bag size (rounded up), and area per bag = bag size / product per 1,000 sq ft x 1,000.
Worked example
5,000 sq ft, 1 lb N per 1,000 sq ft, a 20% N product in 40 lb bags: 1 / 0.20 = 5 lb of product per 1,000 sq ft. Total = 5 x 5 = 25 lb, which is 1 bag. One bag covers 40 / 5 x 1,000 = 8,000 sq ft.
A second case: 10,000 sq ft at 0.75 lb N from a 30% product in 20 lb bags needs 2.5 lb per 1,000 sq ft, 25 lb in total, so 2 bags.
When to use it
Use it when the lawn is already established and you want to know how much fertilizer to spread and how many bags to buy. Many lawn guides suggest roughly 0.5 to 1 lb of nitrogen per 1,000 sq ft per application, which is a typical range rather than a rule. Follow the product label and local guidance for timing and rate.
Common mistakes
- Using the bag weight instead of the nitrogen percentage when working out the rate.
- Entering the whole N-P-K grade as the percentage; only the first number is nitrogen.
- Measuring the area wrongly. Subtract the house, beds and paths from the property area.
- Assuming the bag count matches the area on the bag; your target rate may differ from the label.
How it differs from nearby calculators
The fertilizer NPK calculator handles phosphate and potash targets and lets you work per acre or per hectare, while this page keeps to nitrogen per 1,000 sq ft with bags and coverage. The lawn seed calculator and sod calculator size what you plant when you start a lawn, rather than what you feed it afterwards.
Frequently asked questions
How do I calculate how much fertilizer to apply?
Divide the nitrogen you want per 1,000 sq ft by the nitrogen fraction of the product. For 1 lb N from a 20% product that is 1 ÷ 0.20 = 5 lb of product per 1,000 sq ft.
How much fertilizer for 5,000 square feet?
At 5 lb of a 20-N product per 1,000 sq ft, 5,000 sq ft needs 25 lb, so one 40 lb bag is enough and it would cover 8,000 sq ft.
What does the first number on the bag mean?
Fertilizer grades such as 20-5-10 list nitrogen, phosphorus and potassium as percentages by weight. This calculator uses the first number, nitrogen.
How much nitrogen per application is typical?
Many lawn guides suggest about 0.5 to 1 lb of nitrogen per 1,000 sq ft per application. That is a typical range, not a rule; follow the product label and local guidance.
How much 10-10-10 fertilizer for 1,000 square feet?
To apply 1 lb of nitrogen, divide by the nitrogen fraction: 1 / 0.10 = 10 lb of product per 1,000 sq ft. That one bag application also delivers 1 lb each of phosphate and potash.
How many bags of 30-0-4 do I need for 10,000 square feet?
At 0.75 lb of nitrogen per 1,000 sq ft, a 30 percent product needs 0.75 / 0.30 = 2.5 lb per 1,000 sq ft, so 25 lb in total. With 20 lb bags that is 1.25, so buy 2 bags, and one bag covers 8,000 sq ft.
How much lawn does a 40 lb bag of fertilizer cover?
It depends on the nitrogen percentage and your target rate. At 1 lb N per 1,000 sq ft, a 20 percent bag covers 8,000 sq ft, while a 32 percent bag needs 3.13 lb per 1,000 sq ft and covers 12,800 sq ft.