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Lawn Fertiliser Calculator

Work out how much of a given N-P-K product delivers the nitrogen rate a lawn actually needs.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Product required

7.72 lb of product

Check your inputs

Delivers the stated nitrogen rate. Whether that rate suits your grass depends on species, season and soil test — nitrogen is the one nutrient it is easy to over-apply visibly.

Nitrogen delivered
1.54 lb n
Product in pounds
7.72 lb
Rate per 100 m²
1.75 kg/100 m²
Rate per 1000 ft²
3.58 lb/1000 ft²

At the values currently entered, the product required works out to 3.50 kg of product. Note that lawn area sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. Confidence is moderate: the method is sound, but real materials and site conditions vary. Figures are shown for United States, where IRC 2024 is the governing residential reference; switch the market above if you are building elsewhere.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Typical cool-season lawn nitrogen rate: 25-50 kg N per hectare per application (0.5-1.0 lb N per 1000 ft²) — university turf extension guidance
  • Product application rate = target N rate ÷ (N percentage ÷ 100)

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

What do the three N-P-K numbers mean?
Percentage by weight of nitrogen, phosphorus (as P₂O₅) and potassium (as K₂O). A 20-5-10 bag is 20% nitrogen, so 5 kg of it delivers 1 kg of N. Only the first number sets the application rate for a routine feed.
Why not just use the rate on the bag?
You can, and it is usually reasonable. This exists for when you have a target rate from a soil test or a turf programme and a product whose concentration does not match the one the programme assumed — which is most of the time.
What happens if I apply too much?
Scorch, in stripes matching the spreader pattern, and flush weak growth that invites disease. Fast-release nitrogen in warm weather is the worst case. Split a heavy annual programme into several light applications rather than one large one, and water it in.