Lawn Fertilizer Calculator
Calculate the right amount of fertilizer for your lawn. Enter your lawn size, desired nitrogen application rate, and fertilizer analysis to get pounds needed, bags to buy, and total cost.
Understanding Fertilizer Application Rates
The application rate is measured in pounds of actual nitrogen per 1,000 square feet. Most lawn care experts recommend 0.75 to 1.0 pound of nitrogen per application, with 4 to 6 weeks between applications. To calculate how much product to apply, divide the desired nitrogen rate by the nitrogen percentage on the bag. For example, to apply 1 pound of nitrogen using a 28-0-4 fertilizer: 1 divided by 0.28 equals 3.57 pounds of product per 1,000 square feet.
Fertilizer Types and Timing
Quick-release fertilizers green the lawn in days but can burn if over-applied and require more frequent applications. Slow-release fertilizers feed gradually over 6 to 12 weeks and are safer and more convenient. Organic fertilizers like milorganite release nutrients as soil microbes break them down and also improve soil structure. For best results, apply slow-release fertilizer in fall for cool-season grasses to build root reserves for winter. Spring applications should use a balanced formula, and summer applications should be light if used at all.
Frequently Asked Questions
How much nitrogen does my lawn need per year?
Cool-season grasses need 2 to 4 pounds of nitrogen per 1,000 square feet per year, applied in 2 to 4 split applications. Warm-season grasses need 3 to 6 pounds annually.
What do the NPK numbers mean?
NPK stands for Nitrogen-Phosphorus-Potassium. A 28-0-4 fertilizer contains 28% nitrogen, 0% phosphorus, and 4% potassium by weight. Nitrogen drives leaf growth, phosphorus supports roots, and potassium improves stress tolerance.
When should I fertilize my lawn?
Fertilize cool-season grasses in early fall (September) and late spring (May). Fertilize warm-season grasses from late spring through summer. Avoid fertilizing during drought or extreme heat.