Landscaping
Landscaping Fertilizer Calculator
Calculate fertiliser for a treatment programme including timing across the season.
Result
The first number in an NPK analysis is the percentage of nitrogen by weight, so a 40 lb bag of 24-0-6 contains 9.6 lb of nitrogen. Applying more than about one pound of nitrogen per thousand square feet at once burns the lawn and leaches into groundwater, and many jurisdictions regulate both the rate and the season.
Get a Free Business AuditWhat moves the number
- Nutrient rate per application and the number of applications.
- Grass type and season, which change what is appropriate.
- Local restrictions on timing and content.
Where this one goes wrong
Running the same programme on every lawn. Soil condition, grass species and existing fertility vary between properties, and a uniform programme over-feeds some lawns and under-feeds others.
Questions
About this calculator
How many applications does a lawn need?
It depends on grass type, soil and the standard the customer wants. A programme should follow from a soil condition assessment rather than a default schedule.
Is a soil test worth doing?
For anything beyond a basic programme, yes. It shows what is actually deficient rather than applying a general blend and hoping.
What are the environmental considerations?
Runoff into watercourses is the main one, and it is regulated in many areas. Application timing relative to rainfall and proximity to water both matter.
The formula
product = (area / 1000) x nitrogen rate / nitrogen percentage
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How to use this calculator
- Length (ft) (ft). Enter your own figure; the page starts at 60 ft.
- Width (ft) (ft). Enter your own figure; the page starts at 40 ft.
- Nitrogen in the bag (%) (%). Enter your own figure; the page starts at 24%.
- Waste allowance (%). Extra for cuts, breakage and offcuts.
- Cost per bag ($). Enter your own figure; the page starts at $34.
- Nitrogen rate (lb per 1,000 sq ft). Enter your own figure; the page starts at 1.
The result updates as you type, so you can try a figure, see what it does to bags needed, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Length (ft) | 60 ft |
| Width (ft) | 40 ft |
| Nitrogen in the bag (%) | 24% |
| Waste allowance | 0% |
| Cost per bag | $34 |
| Nitrogen rate (lb per 1,000 sq ft) | 1 |
| Bag weight (lb) | 40 lb |
What comes out
| Result | Value |
|---|---|
| Bags needed main result | 1 |
| Area | 2,400.0 |
| Area including waste | 2,400.0 |
| Estimated material cost | $34 |
| Product needed | 10.0 |
| Nitrogen applied | 2.4 |
For 2,400.0 square feet at 1 lb of nitrogen per thousand you need 10.0 lb of product, which is 1 bags.
How sensitive the answer is
Holding everything else steady and changing only cost per bag, this is what happens to bags needed. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Cost per bag ($) | Bags needed |
|---|---|
| $17 | 1 |
| $25.5 | 1 |
| $34 example above | 1 |
| $51 | 1 |
| $68 | 1 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Length (ft) (ft)
- Measured in ft, starting at 60 ft.
- Width (ft) (ft)
- Measured in ft, starting at 40 ft.
- Nitrogen in the bag (%) (%)
- A percentage, starting at 24%.
- Waste allowance (%)
- Extra for cuts, breakage and offcuts.
- Cost per bag ($)
- A money amount, starting at $34.
- Nitrogen rate (lb per 1,000 sq ft)
- A number, between 0 and 5, starting at 1.
- Bag weight (lb) (lb)
- Measured in lb, between 0 and 100, starting at 40 lb.
What the results tell you
| Result | What it is |
|---|---|
| Bags needed | The headline result. A number. |
| Area | A decimal figure. |
| Area including waste | A decimal figure. |
| Estimated material cost | A money figure. |
| Product needed | A decimal figure. |
| Nitrogen applied | A decimal figure. |
Seasonality is not in this
Coverage and material figures assume the area you enter. Slope, access for machinery, existing growth and the time of year all affect both quantity and labour, and none of them appear in a calculation like this.
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