Lawn Fertilizer Calculator
Calculate fertilizer bags needed by lawn size, grass type, and N-P-K ratio.
By Konstantin Iakovlev · Updated September 2026 · Source: Clemson Cooperative Extension — Bermudagrass Maintenance Calendar
Fertilizer Needed
20.8 lbs
Bags Needed (50 lb)
1
Total N Applied
5.0 lbs
Est. Cost
$35.00
Application Details
| Fertilizer N-P-K | 24-0-4 |
| Total Fertilizer | 20.8 lbs |
| Per 1,000 sq ft | 4.2 lbs |
| Spreader Suggestion | Setting 3–4 (rotary), check bag |
Cool Season Schedule
| Application 1 | Early Spring (Mar-Apr) |
| Application 2 | Late Spring (May) |
| Application 3 | Early Fall (Sep) |
| Application 4 | Late Fall (Nov) |
Season Tip
Apply when grass is actively growing. Use slow-release for sustained feeding.
Always follow the fertilizer bag instructions for exact spreader settings. Water lawn after application. Avoid fertilizing during drought or extreme heat. Check local regulations for phosphorus restrictions.
Use the Lawn Fertilizer Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.
Disclaimer: This calculator is for informational purposes only. Results are estimates from the numbers you enter and the assumptions described on this page; check them against local building codes, product specifications and current prices, and have structural, electrical or gas work designed or checked by a licensed professional.
How It Works
Figuring out how many bags of fertilizer a lawn actually needs sits between two failure modes. Too much scorches the grass and washes nutrients into the environment; too little leaves you with thin, patchy turf. Feed your lawn size, the N-P-K ratio printed on the bag and the nitrogen rate you want per application into this tool, and it works out how much product to spread and when.
Calculation starts with the pounds of actual nitrogen (N) you want to put down per 1,000 square feet in one application, usually 1/2 to 1 pound. That rate is scaled up by your lawn area to find the nitrogen for the whole yard, divided by the nitrogen percentage in your fertilizer (the first number of the N-P-K ratio) to get pounds of product, and divided by a 50 lb bag for the bag count. The grass type sets the application calendar: spring and fall for cool-season grasses, May through August for warm-season grasses.
Read the label closely, since N-P-K ratios swing widely even between products from the same brand. Hold off on spreading fertilizer ahead of heavy rain, which carries nutrients off as runoff and into local waterways. And do not assume every grass behaves alike: warm-season types such as Bermuda generally call for more nitrogen than cool-season grasses like Fescue.
Example: Fertilizing a 5,000 sq ft Bermuda Grass Lawn
- 1 You have a 5,000 sq ft Bermuda grass lawn and want to use a 16-4-8 fertilizer at 1 lb of nitrogen per 1,000 sq ft per application.
- 2 Nitrogen per application: 5 * 1 = 5 lbs. Product: 5 / 0.16 = 31.25 lbs of 16-4-8, which fits in one 50 lb bag. (Clemson Extension's shortcut gives the same answer: 100 / 16 = 6.25 lbs of product per 1,000 sq ft.)
- 3 Clemson recommends 2 to 4 lbs of actual nitrogen per 1,000 sq ft per growing season for bermudagrass, split into applications of 1/2 to 1 lb from May to mid-August, so this lawn takes 2 to 4 such applications a year: 62.5 to 125 lbs of product, or 2 to 3 bags.
- 4 At the calculator's $35 per 50 lb bag, one application costs about $35 and a full season $70 to $105. Base the phosphorus and potassium on a soil test, and skip nitrogen before green-up in spring, when a late frost can damage the new growth.
Source: Clemson Cooperative Extension — Bermudagrass Maintenance Calendar · Last updated: September 2026
Frequently Asked Questions
How much fertilizer do I need per 1,000 square feet?
When should I fertilize my lawn?
What do the three numbers on fertilizer mean?
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