Lawn Fertilizer Calculator: Pounds of Product from Nitrogen

This calculator converts a nitrogen target into pounds of fertilizer product. Enter the lawn area, the pounds of nitrogen you want per 1,000 ft², and the nitrogen percentage (the first number on the bag); you get the product to spread on the whole lawn and per 1,000 ft².

Formula

Product per 1,000 ft² = nitrogen target ÷ (nitrogen percentage ÷ 100). Product for the lawn = product per 1,000 ft² × area ÷ 1,000. The three numbers on a bag (N-P-K) are the percentages by weight of nitrogen, phosphate and potash.

• a: lawn area in square feet
• n: pounds of actual nitrogen wanted per 1,000 ft² for this application
• pct: nitrogen percentage of the product

Worked Example

A 5,000 ft² lawn, 1 lb of nitrogen per 1,000 ft², a 24-0-6 product.

1. Per 1,000 ft² = 1 ÷ 0.24 = 4.17 lb of product
2. Whole lawn = 4.1667 × 5,000 ÷ 1,000 = 20.83 lb
3. In kilograms: 20.83 × 0.45359237 = 9.45 kg

How to use the result

Weigh out the product, set the spreader as the label says, and check how much is left after the first pass. Your nitrogen target should come from the product label, a soil test or local extension advice for your grass and season.

Limits and common mistakes

• Enter the nitrogen percentage, not the whole N-P-K string: for 24-0-6 enter 24.
• Do not raise the target to make the lawn greener faster; follow the label’s maximum per application.
• Keep fertilizer off paved surfaces and away from water, and sweep any spill back onto the lawn.

Frequently Asked Questions

How much 10-10-10 do I need for 1 lb of nitrogen per 1,000 ft²?

1 ÷ 0.10 = 10 lb of product per 1,000 ft².

What do the three numbers on fertilizer mean?

The percentages of nitrogen (N), phosphate (P2O5) and potash (K2O) by weight.

Can I use this for slow-release fertilizer?

Yes, the arithmetic is the same; release speed does not change the nitrogen content.

Is the result per application or per year?

Per application, for the target you enter.

in a | Lawn area | ft² | 5000 | 0
in n | Nitrogen target | lb N per 1,000 ft² | 1 | 0 | 5
in pct | Nitrogen in the product (first number) | % | 24 | 0.1 | 100
out tot | Fertilizer for the lawn | lb | n / (pct / 100) * a / 1000 | 2
out per | Fertilizer per 1,000 ft² | lb | n / (pct / 100) | 2
out kg | Fertilizer for the lawn | kg | tot * 0.45359237 | 2