Measure Your Lawn
Measure the total turf area (subtract beds, sidewalks, and driveways).
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A lawn fertilizer calculator determines the exact pounds of product to spread per 1,000 square feet from your bag's N-P-K analysis and desired nitrogen rate. Enter lawn size, fertilizer analysis, and target application rate to get precise product quantities that prevent over-application and lawn burn.
Lawn & Fertilizer
Total area minus beds, driveway, and hardscape
Bag N-P-K Analysis
Find the three numbers on the front of the bag (e.g. 24-0-4). The second and third are phosphate (P₂O₅) and potash (K₂O), not elemental phosphorus and potassium.
Most cool-season lawns do best at 1 lb N per 1,000 sqft. Rates above that burn turf, so this list stops there; to feed more over a season, apply again 4-6 weeks later.
Application Rate
Product / 1,000 sqft—
Total Product—
Bags Needed—
Actual N Applied—
Phosphate (P₂O₅) Applied—
Potash (K₂O) Applied—
How It Works
Read the Label
Find the N-P-K analysis on the bag (e.g. 24-0-4) and the bag weight.
Set Your Rate
Choose how many pounds of nitrogen per 1,000 sqft. Standard is 1 lb N.
Spread It Right
Get exact product weight per 1,000 sqft and total bags needed for your lawn.
Why Fertilizer Math Matters
Over-fertilizing burns turf and pollutes waterways. Under-fertilizing wastes money on product that doesn't move the needle. The bag's N-P-K ratio tells you the percentage of nitrogen, phosphorus, and potassium by weight — but the number most homeowners need is how many pounds of product to put down per 1,000 square feet to hit their nitrogen target. GreenCalc does the division for you: enter your bag's analysis, your lawn size, and your desired application rate. Every calculation runs in your browser.
Frequently Asked Questions
How do you read a fertilizer bag's N-P-K numbers?
The three numbers on a fertilizer bag represent the percentage by weight of nitrogen (N), phosphate (P₂O₅), and potash (K₂O). Only the first is the element itself; the second and third are oxide forms, so they need converting before you compare them against a soil test or an ordinance written in elemental terms. A 50-lb bag of 24-0-11 contains 24% nitrogen (12 lbs actual N), 0% phosphate, and 11% potash (5.5 lbs K₂O, which is 4.57 lbs actual K, since K₂O is 83% potassium by weight). To get 1 lb of nitrogen per 1,000 sqft, you would apply 4.17 lbs of this product per 1,000 sqft.
How much nitrogen should I apply to my lawn per application?
Most turf grasses do best with 0.5-1.0 lb of actual nitrogen per 1,000 sqft per application. Cool-season grasses (fescue, bluegrass) need 2-4 lbs N total per year across 3-4 applications. Warm-season grasses (bermuda, zoysia) need 3-5 lbs N total per year. Never exceed 1 lb N per 1,000 sqft in a single application — it can burn the grass.
When is the best time to fertilize a lawn?
For cool-season grasses: early fall (September) is the most important application, followed by late fall (November) and spring (April). For warm-season grasses: apply after the grass greens up in spring (April-May) through summer, with the last application 6 weeks before first frost. Never fertilize dormant grass.