Lawn Fertilizer Calculator
Enter the lawn's length and width, the nitrogen percent from the bag and a nitrogen rate, and get the pounds of product on each thousand square feet, for the whole lawn and the bags to buy, with the area one bag covers.
Estimates for planning, not professional advice. Read the full notice.
The drawing did not open. Length and width are still here.
Lawn: shape and size
Skip the drawingDrag a round corner to move it. The small hollow diamond on a side is its curve handle: drag it across the side to curve the side (it is not a corner). To add a corner (a new point), tap the side itself, then choose Add a point here. Tapping a corner or a side opens its actions. Drag empty space to move the view; pinch, or Ctrl and the mouse wheel, to zoom. The keys are listed under Keys.
Keys
- Tab
- next corner; each says how far it is from corner 1
- Arrow keys on a corner
- move it one square; ten with Shift; 1/16 in with Alt
- Delete or Backspace
- remove the corner; its two sides join in one straight side
- + on a corner
- add a corner halfway along the next side
- Arrow keys on the drawing
- move the view; farther with Shift
- + and - on the drawing
- zoom in and out
- 0 on the drawing
- show the whole shape
- Ctrl+Z (Cmd+Z on a Mac)
- undo, except inside a typed field (it keeps its own)
- Ctrl+Shift+Z or Ctrl+Y
- redo
- Escape while dragging
- put it back where it was
- Enter on a corner or side
- go to its actions
- Escape in the actions
- close them and go back to the drawing
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- Area
- 5,000 ft²
- Perimeter
- 300 ft
- Cut-out edges
No area until the shape is fixed.
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
Shape: Rectangle Change
Sides
Corners
Cut-outs
Feet and inches, like 12' 6"
Example: a rectangular lawn
1 50 lb bag
- Actual nitrogen for the lawn 5 lb
- Product for the lawn 27.778 lb
- Product on each thousand square feet 5.556 lb
- Area one bag covers 9,000 ft²
- Bags at the low end of the published range, shown beside the count above, which uses the high end 1 × 50 lb bag
Your project
Enter a size to see your total.
Each product is rounded up once for the whole project, so the total can be less than the items bought alone added together. A line counted from a cut layout (sheets, boards or tiles laid out piece by piece) is counted for each item and added.
Product, coverage and the published value
These numbers follow the sizes above for every item in the list.
Shopping list
| Item | Size | Buy |
|---|---|---|
| Lawn fertilizer, by the bag | 50 lb bag | 1 |
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Worked example: a rectangular lawn
Show the working
- Nitrogen for the lawn: thousands of square feet times the rate 5 thousands of sq ft × 1 lb N per 1,000 sq ft[1] = 5 lb
- Product: the nitrogen divided by the decimal value of the analysis 5 lb ÷ 0.18 = 27.778 lb
- Bags: product over the bag size, rounded up once 27.778 lb ÷ 50 lb = 1 × 50 lb bag
- Area one bag covers: bag pounds times the decimal value, over the rate 50 lb × 0.18 ÷ 1 lb N per 1,000 sq ft[1] = 9,000 ft²
Assumptions
The figures behind the example. Sourced figures link to their source below; a default is a starting value to check against your label or supplier.
| Assumption | Value | Details and changes |
|---|---|---|
| Nitrogen in the product, percent | 18 % | |
| Default The first number of the analysis printed on the bag. Check your label. | ||
| Nitrogen rate, Purdue Extension, low end of the usual range | 0.5 lb N per 1,000 sq ft[1] | |
| Purdue Extension: the target application rate is normally between 0.5 and 1.0 pound of actual nitrogen per 1,000 square feet, and in general no more than 1 pound of actual N in any one single application. | ||
| Nitrogen rate, Purdue Extension, high end of the usual range | 1 lb N per 1,000 sq ft[1] | |
| Purdue Extension: the target application rate is normally between 0.5 and 1.0 pound of actual nitrogen per 1,000 square feet, and in general no more than 1 pound of actual N in any one single application. | ||
| Nitrogen in one single application, Purdue Extension | 1 lb N per 1,000 sq ft[1] | |
| Purdue Extension: the target application rate is normally between 0.5 and 1.0 pound of actual nitrogen per 1,000 square feet, and in general no more than 1 pound of actual N in any one single application. | ||
| Fertilizer bag size | 50 lb | |
| Default Check your label or supplier. | ||
Feet and inches, like 12' 6"
Product on each thousand square feet
Pounds of product on each thousand square feet for four analyses at three nitrogen rates
| Nitrogen in the product | 0.5 lb N | 0.75 lb N | 1 lb N |
|---|---|---|---|
| 10 percent | 5 lb | 7.5 lb | 10 lb |
| 18 percent | 2.778 lb | 4.167 lb | 5.556 lb |
| 24 percent | 2.083 lb | 3.125 lb | 4.167 lb |
| 29 percent | 1.724 lb | 2.586 lb | 3.448 lb |
Each cell is the nitrogen rate divided by the decimal value of the analysis. The analyses are examples; yours is on the bag.
Area a bag covers
Area covered by one bag of the starting size for four analyses at three nitrogen rates
| Nitrogen in the product | 0.5 lb N | 0.75 lb N | 1 lb N |
|---|---|---|---|
| 10 percent | 10,000 ft² | 6,667 ft² | 5,000 ft² |
| 18 percent | 18,000 ft² | 12,000 ft² | 9,000 ft² |
| 24 percent | 24,000 ft² | 16,000 ft² | 12,000 ft² |
| 29 percent | 29,000 ft² | 19,333 ft² | 14,500 ft² |
Bag pounds times the decimal value of the analysis, over the rate.
Questions
How many pounds of fertilizer per 1,000 square feet?
Divide the nitrogen rate you want by the decimal value of the analysis, the nitrogen percent divided by one hundred. The first table above lists the product pounds for four analyses at three rates, and the calculator does the same for yours.
How far does a bag of lawn fertilizer go?
A bag covers its pounds times the decimal value of the analysis, divided by the rate, in thousands of square feet. The second table lists the area for a bag of the starting size, and the calculator shows it for the bag you choose.
What is the most nitrogen in one application?
Purdue Extension says "In general, no more than 1 pound of actual N should be applied in any one single application." The calculator compares your rate with that published value and says within or outside; it does not judge it. Check local requirements.
Sources (1)
-
Fertilizing Established Cool-season Lawns (AY-22-W) (opens in new tab), Purdue Extension, AY-22-W.
Code or government.
“The target application rate you want to apply (normally between 0.5 and 1.0 pound of actual N per 1,000 square feet).”
“In general, no more than 1 pound of actual N should be applied in any one single application.”
“Divide the target application rate (0.5 pound) by the decimal value from step 1.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 1)
These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.
Sources
- [1] Purdue Extension, Fertilizing Established Cool-season Lawns (AY-22-W). Checked November 12, 2026. https://ag.purdue.edu/department/hla/extension/extension-publications-library/ext-pubs/ay-22-w.html