Lawn Fertilizer Calculator
Turn the numbers on a fertilizer bag into how many pounds to spread and how many bags to buy.
How to use this fertilizer calculator
Measure your lawn and pick its shape. Then look at the three numbers on the bag, such as 24-0-11. They're the percentages of nitrogen, phosphorus and potassium. Enter the first number (nitrogen), because lawn feeding is usually planned around nitrogen.
Most lawns do well with about 1 lb of nitrogen per 1,000 sq ft per feeding. Use 0.5 lb for a light feeding or a slow-growing grass. The calculator works out how many pounds of the actual product to spread to hit that amount.
Typical feeding schedule
| Grass type | Best time to feed | Feedings per year |
|---|---|---|
| Cool-season (fescue, bluegrass, rye) | Early fall, late fall, light spring | 2 to 4 |
| Warm-season (Bermuda, zoysia, St. Augustine) | Late spring through summer | 2 to 4 |
The math behind it
Pounds of product = lawn area ÷ 1,000 × nitrogen rate ÷ (nitrogen % ÷ 100). Bags = pounds ÷ bag size, rounded up.
Example: a 100 × 50 ft lawn is 5,000 sq ft. To apply 1 lb of nitrogen per 1,000 sq ft with a 24-0-11 fertilizer, you need 5 ÷ 0.24 ≈ 20.8 lb of product, which is one 32 lb bag.
Often used together
Quick answers
What do the three numbers on fertilizer mean?
They're the percentages of nitrogen (N), phosphorus (P) and potassium (K) by weight. A 50 lb bag of 20-5-10 contains 10 lb of nitrogen, 2.5 lb of phosphorus and 5 lb of potassium.
How much area does a bag of fertilizer cover?
The bag usually says, often 5,000 sq ft. You can check it here: enter the bag's weight and nitrogen percentage, and see what size lawn one bag covers at your chosen rate.
Can I put down too much fertilizer?
Yes. Too much can burn the grass and wash into streams. It's better to under-feed slightly and repeat later than to over-apply.