Lawn fertilizer calculator

Enter the three numbers on the bag, your lawn size and the rate of nitrogen you want. You get the pounds of product per 1,000 sq ft, the total, and how many bags to buy.

The three numbers on the bag (N-P-K)

Lawn size

Nitrogen per 1,000 sq ftBag weight (lb)

Spread per 1,000 sq ft

4.17 lb

20.8 lb for the whole lawn (5,000 sq ft).

Bags to buy: 1 (you use 42% of it)
Nitrogen applied: 5 lb
Phosphate (P₂O₅) applied: 0 lb
Potash (K₂O) applied: 2.08 lb

Check the label: its rate and spreader setting come first. Split the total across two passes at right angles for even cover.

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How it works

Lawn recommendations are given in pounds of nitrogen (N) per 1,000 square feet, but you spread product, not nitrogen. The first number on the bag is the percentage of nitrogen by weight, so you divide the rate you want by that percentage.

Example from Iowa State University Extension: to apply 1 lb of N per 1,000 sq ft with a 32-0-4 fertilizer, spread 1 ÷ 0.32 = 3.125 lb of product per 1,000 sq ft. On a 5,625 sq ft lawn that is 3.125 × 5,625 ÷ 1,000 = 17.58 lb.

The same product also carries phosphate (P₂O₅) and potash (K₂O) in the proportion of its second and third numbers; the tool shows how much of each you apply.

Product per 1,000 sq ft = N rate ÷ (N% ÷ 100). Total = product per 1,000 sq ft × lawn area ÷ 1,000.

Good to know

The right nitrogen rate depends on your grass, your region and the season. A soil test or your state extension office gives the best number.
Read the bag: its label rate and spreader settings come first, and some states limit phosphorus on lawns.
Keep fertilizer off driveways and sidewalks, and sweep it back onto the grass.

Frequently asked questions

How much fertilizer do I need for 1,000 square feet?

Divide the pounds of nitrogen you want by the nitrogen percentage on the bag. For 1 lb of N with a 24-0-10 product: 1 ÷ 0.24 = 4.17 lb of product per 1,000 sq ft.