Fertilizer Calculator
Work out how much lawn fertilizer you need to hit a target nitrogen rate, by area and product.
What you need
2.0lb
Product needed — Total weight to buy at the rate you selected.
- Area being treated
- 200.0 sq ft
- Bags needed
- 1
Estimates for planning. Confirm quantities with your supplier before ordering — see the assumptions below for the figures used.
How to use the fertilizer calculator
Lawn fertiliser is applied to deliver a target amount of nitrogen — usually 1 pound of actual nitrogen per 1,000 square feet per application. How much product that takes depends on the first number in the N-P-K analysis. Pick your target and this calculator does the conversion.
What this calculator assumes
Every estimate depends on figures that vary by supplier and conditions. These are the ones used here, so you can sanity-check the result against your own quote.
- Rates are expressed per 1,000 square feet, the standard used on North American product labels.
- Bag counts are rounded up. Buying one spare bag is usually worth it — running short mid-application leaves visible stripes.
- Rates target roughly 1 pound of actual nitrogen per 1,000 square feet, the standard single-application rate for most lawns.
- Total annual nitrogen should generally stay between 2 and 4 pounds per 1,000 square feet, split across several applications.
- Slow-release products can be applied at higher single rates than quick-release without burning. Always follow the bag.
Frequently asked questions
How do I convert an N-P-K number into pounds of product?
Divide your target nitrogen by the first number as a decimal. For 1 pound of nitrogen from a 16-4-8 product: 1 ÷ 0.16 = 6.25 pounds of product per 1,000 square feet. The same arithmetic works for phosphorus and potassium using the second and third numbers.
How much fertilizer does my lawn need per year?
Two to four pounds of actual nitrogen per 1,000 square feet annually for most cool-season lawns, split into three or four applications. Warm-season grasses in long growing seasons can take more. Over-applying pushes soft growth, invites disease and runs off into waterways.
Should I water after fertilizing?
For granular products, yes — a quarter inch of water moves the granules off the leaf blades and into the soil, which prevents burn and starts the release. Do not water so heavily that you flush it past the root zone.
How do I measure an irregular lawn?
Break it into rectangles, circles and triangles, calculate each and add them up. Subtract large features like a patio, driveway or pool — but do not bother subtracting flower beds smaller than a few square yards.
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