Fertilizer Calculator by N-P-K and Lawn Size

How to use

1. Copy the three numbers off the bag — e.g. 29-3-4 — into N, P and K.
2. Enter lawn size: length × width or a direct area, in sq ft or m².
3. Set the target nitrogen rate (0.5–1.0 lb per 1,000 sq ft is typical).
4. Read product weight, bags to buy, and the P and K you are actually applying.

About this tool

Bag fertilizer is priced the same whether you apply it right or wastefully, and the N-P-K on the label only means something once you tie it to a rate. This fertilizer calculator does the agronomy: enter the three label numbers, your lawn size, and a target nitrogen rate in pounds per 1,000 square feet — 0.5 to 1.0 per application is the standard lawn range. It returns the exact product weight needed, bags to buy for your bag size, the actual nitrogen delivered, and as a bonus the phosphorus and potassium your single application drops per 1,000 square feet, which is how you catch bags that overfeed P your soil test never asked for. The schedule guidance splits anything over a pound of nitrogen into repeat passes and spaces applications six to eight weeks apart, cool-season versus warm-season style. Run the numbers before you buy, not after the spreader is loaded. Educational estimate, not professional agronomy advice.

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