Lawn Fertilizer Numbers, Explained

The three numbers on every bag are the percent of nitrogen, phosphate and potash by weight. Here's how to turn them into pounds per 1,000 sq ft.

How to Read N-P-K

A bag labeled 20-0-10 is 20% nitrogen (N), 0% phosphate (P₂O₅) and 10% potash (K₂O). A 50-lb bag holds 10 lbs of nitrogen and 5 lbs of potash. The rest is carrier that helps it spread evenly.

Lawn feeding is measured in pounds of nitrogen per 1,000 sq ft, not pounds of product. To get the product rate, divide the nitrogen you want by the first number and multiply by 100: 1 lb N from a 20-0-10 is 1 ÷ 20 × 100 = 5 lbs of product per 1,000 sq ft.

Most established cool-season lawns use about 2–4 lbs of nitrogen per 1,000 sq ft per year, mostly in fall. Warm-season grasses like bermuda use more, mostly in summer. Single applications usually run 0.5–1 lb N. Go lighter with quick-release nitrogen and in hot weather.

Fertilizer Calculator

N (%)

P (%)

K (%)

lb N per 1,000 sq ft

Lawn size (sq ft)

Bag size (lb)

Spread 5 lb per 1,000 sq ft, 25 lb for 5,000 sq ft (0.5 bags).

Delivers 1 lb N, 0 lb P₂O₅ and 0.5 lb K₂O per 1,000 sq ft. Never exceed the label rate.

Lawn fertilizer (N + K)

32-0-43.13 lb / 1,000 for 1 lb N 32-0-103.13 lb / 1,000 for 1 lb N 30-0-43.33 lb / 1,000 for 1 lb N 29-0-43.45 lb / 1,000 for 1 lb N 30-0-63.33 lb / 1,000 for 1 lb N 24-0-64.17 lb / 1,000 for 1 lb N 24-0-114.17 lb / 1,000 for 1 lb N 22-0-104.55 lb / 1,000 for 1 lb N 20-0-105 lb / 1,000 for 1 lb N 16-0-86.25 lb / 1,000 for 1 lb N

Nitrogen only

46-0-0Urea2.17 lb / 1,000 for 1 lb N 21-0-0Ammonium sulfate4.76 lb / 1,000 for 1 lb N 20-0-05 lb / 1,000 for 1 lb N 30-0-03.33 lb / 1,000 for 1 lb N

Starter fertilizer

18-24-125.56 lb / 1,000 for 1 lb N 24-25-44.17 lb / 1,000 for 1 lb N 16-32-66.25 lb / 1,000 for 1 lb N

Balanced / all-purpose

10-10-1010 lb / 1,000 for 1 lb N 13-13-137.69 lb / 1,000 for 1 lb N 15-15-156.67 lb / 1,000 for 1 lb N 20-20-205 lb / 1,000 for 1 lb N 20-10-105 lb / 1,000 for 1 lb N 20-20-105 lb / 1,000 for 1 lb N 20-5-105 lb / 1,000 for 1 lb N 16-4-86.25 lb / 1,000 for 1 lb N

Potassium

0-0-62Muriate of potash1.61 lb / 1,000 for 1 lb K₂O 0-0-50Sulfate of potash2 lb / 1,000 for 1 lb K₂O 7-0-20Stress blend14.3 lb / 1,000 for 1 lb N

Organic

6-4-0Milorganite16.7 lb / 1,000 for 1 lb N

Carrier / low analysis

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