Lawn Fertilizer Calculator: How Much, How Often, When

Type the three numbers on the bag, your lawn and how much nitrogen you want to put down. You get the pounds of fertilizer and the bags, then how many times a year each state’s extension service feeds that grass, and when.

17 lb of 29-0-5 — 1 bag of 40 lb — see when ↓

The bag’s numbers

Grass

N-P-K, the big three numbers on the front. The first is the percent nitrogen: 29-0-5 is 29% nitrogen, no phosphorus, 5% potash.

Lawn size sq ft

Bag size lb

Nitrogen this time lb per 1,000 sq ft

The nitrogen in the bag

The label’s “derived from” and “water insoluble nitrogen” lines say which. A soil test report’s number goes in the nitrogen field.

Kentucky bluegrass · 29-0-5 · 5,000 sq ft

17 lb of 29-0-5 — 1 bag of 40 lb3.45 lb per 1,000 sq ft puts down 1 lb of nitrogen per 1,000 sq ft, with 0.17 lb of potash, across 5,000 sq ft.

How much a year — and it depends who you ask

Who	Where	N a year (lb per 1,000 sq ft)	Applications like this one
K-State	Kansas	2–4	2–4
Clemson	South Carolina Piedmont and mountains	1–3	1–3
UConn	Connecticut	2	2

When

K-State, 1 a year: early September.
K-State, 2 a year: early May and early September.
K-State, 3 a year: early May, early September and late season (about a week after the last mowing).
K-State, 4 a year: early May, mid to late June, early September and late season (with summer irrigation).
Missouri, 2 a year: early September, then early November or April–May.
Missouri, 4 a year: May, September, October and November.
UConn: September, and late April through the end of May.

Clemson: “The pounds of actual N in every fertilizer can be determined by dividing the percent N listed on the label into 100.” Fertilizing Lawns (HGIC 1201, revised October 2019)
K-State: “Where clippings are returned to turf, apply 1/4 less actual mineral nutrients than when clippings are not returned.” Lawn Problem Solver — Fertilizing (Kansas State University, updated April 2026)
K-State: “Regardless of the fertilization schedule used, make sure that an application occurs to cool season turf in late summer or early fall.” Lawn Problem Solver — Fertilizing (Kansas State University, updated April 2026)
UConn: “A law passed in 2013, limits the amount of phosphorus that can be applied to established lawns because it is the number one inland freshwater pollutant.” Fall is a Great Time to Lime and Fertilize Lawns (September 20, 2025)

Each source’s own words

K-State: “Table 8. Pounds of actual nitrogen per 1,000 square feet per year required by different turf species — Improved Kentucky Bluegrass 2 – 4; Common Kentucky Bluegrass 1 – 2” Lawn Problem Solver — Fertilizing (Kansas State University, updated April 2026) · checked 2026-09-27
Clemson: “Piedmont and Mountain Areas of the South Carolina — Tall Fescue/Ky Blue — Total Yearly N (lbs) 1-3” Fertilizing Lawns (HGIC 1201, revised October 2019) · checked 2026-09-27
UConn: “If grass clippings are left in place then only 2 pounds of nitrogen per 1000 square feet of turf area will be needed each year.” Fall is a Great Time to Lime and Fertilize Lawns (September 20, 2025) · checked 2026-09-27
K-State: “Table 9. Cool season turfgrass fertilization schedule — 1 application: Early Sept.” Lawn Problem Solver — Fertilizing (Kansas State University, updated April 2026) · checked 2026-09-27
K-State: “Table 9. Cool season turfgrass fertilization schedule — 2 applications: Early May, Early Sept.” Lawn Problem Solver — Fertilizing (Kansas State University, updated April 2026) · checked 2026-09-27
K-State: “Table 9. Cool season turfgrass fertilization schedule — 3 applications: Early May, Early Sept., Late Season. **Late season application should be applied approximately 1 week following the final mowing of the season.” Lawn Problem Solver — Fertilizing (Kansas State University, updated April 2026) · checked 2026-09-27
K-State: “Table 9. Cool season turfgrass fertilization schedule — 4 (with summer irrigation): Early May, Mid to Late June, Early Sept., Late Season” Lawn Problem Solver — Fertilizing (Kansas State University, updated April 2026) · checked 2026-09-27
Missouri: “Apply one pound of nitrogen per 1000 square feet in early September and again in early November or April-May.” Lawn and Garden Soil Test Interpretations and Fertilizer Recommendation Guide (MP733) · checked 2026-09-27
Missouri: “For lawn maintenance, apply three fourths to one pound of nitrogen per 1000 square feet at each of the following times – May, September, October and November.” Lawn and Garden Soil Test Interpretations and Fertilizer Recommendation Guide (MP733) · checked 2026-09-27
UConn: “The best times to fertilize lawns are in September and in late April through the end of May.” Fall is a Great Time to Lime and Fertilize Lawns (September 20, 2025) · checked 2026-09-27

Sources checked 2026-09-27. Spreader settings are on the bag — they are the maker’s, not ours.

Quick answer: divide the pounds of nitrogen you want per 1,000 square feet by the bag’s first number as a decimal. For 1 lb of nitrogen from a 29-0-5, that is 1 ÷ 0.29 = 3.45 lb of fertilizer per 1,000 sq ft, or 17 lb for a 5,000 sq ft lawn. K-State and UConn both say no more than 1 lb of quick-release nitrogen per 1,000 sq ft at one time. How many times a year depends on the grass and on who you ask: K-State puts Kentucky bluegrass at 2 to 4 lb of nitrogen a year, Clemson at 1 to 3, and UConn at 2 if you leave the clippings. For cool-season grass, every schedule includes early fall.

How to use it

Type the three numbers from the front of the bag, pick the grass, and type the lawn’s size (the lawn size calculator measures it) and the bag’s weight. Leave the nitrogen at 1 lb per 1,000 sq ft unless a soil test report or your extension office gives you another figure. The answer is the fertilizer for this one application and how many bags that takes. Under it, each source’s yearly range for your grass turns into a number of applications like this one, followed by each source’s calendar.

Reading the bag

The three numbers are always nitrogen, phosphate and potash, in that order, as percentages of the bag’s weight. A 29-0-5 is 29% nitrogen, no phosphate and 5% potash; a 50 lb bag of it holds 14.5 lb of nitrogen. Clemson’s rule for the arithmetic is the one this tool uses: “The pounds of actual N in every fertilizer can be determined by dividing the percent N listed on the label into 100.” Divide 100 by the first number and you get the pounds of that product that put down 1 lb of nitrogen. UConn notes that lawn fertilizers sold in Connecticut typically read 30-0-4, 29-0-5 or 10-0-6. The zero in the middle is not an accident: Connecticut’s 2013 law limits phosphorus on established lawns because, UConn says, it is the number one inland freshwater pollutant.

How much a year: the states disagree

Every source here measures the year in pounds of nitrogen per 1,000 square feet, and none of them gives the same number:

K-State (Kansas): Kentucky bluegrass, tall fescue and perennial ryegrass 2–4 lb; fine fescues 1–3; Bermuda 4–8; zoysia and St. Augustine 2–4; buffalograss 0–2.
Clemson (South Carolina): tall fescue and bluegrass 1–3; Bermuda and zoysia 3–5; St. Augustine 1–4; centipede 1–2 in the Piedmont and ½–2 on the coast; bahia 1–4.
UConn (Connecticut): 2 lb a year for a cool-season lawn if the clippings stay on it.

The differences are real. Clemson says the higher rates are for people who want the best-looking lawn, and may also be needed on sandy soil and in the longer growing seasons near the coast; lawns on heavier clay with short seasons may do fine at the low end. K-State adds that where clippings stay on the lawn you can use a quarter less, and that shade wants the low end. Centipede is the one to be careful with: Clemson says more than 2 lb a year “often results in” what it calls centipedegrass decline.

When

For cool-season grass (bluegrass, fescue, ryegrass), K-State’s schedule starts from one early-September feeding and adds early May, then a late-season feeding about a week after the last mowing, then mid to late June for an irrigated lawn. Missouri’s soil lab says early September and early November (or April–May) for an average lawn, and May, September, October and November for a high-quality one. UConn says September, and late April through the end of May. The one thing they all share is the early fall feeding: K-State says a cool-season lawn should get one in late summer or early fall whatever else you do.

For warm-season grass (Bermuda, zoysia, St. Augustine, centipede), feeding starts once the grass is growing in spring. K-State says monthly after that while it grows. Missouri says late May and mid-July for an average lawn, or late May or early June, then July and August for a better one. Clemson’s centipede example is May and August. Before the first spring feeding, a soil test tells you whether the lawn needs phosphorus, potash or lime as well.

What it does not do

It does not give spreader settings. Those are the bag maker’s, printed on the bag, and they differ by spreader model. It does not tell you to add phosphorus or potash; a soil test does. And it never adds the yearly ranges together into one “your lawn needs” figure. They are three states’ answers, and yours is whichever describes your lawn and your climate best.

Common questions

How much fertilizer do I need for my lawn?

Divide the pounds of nitrogen you want per 1,000 square feet by the bag’s first number as a decimal, then multiply by your lawn’s size in thousands of square feet. For 1 lb of nitrogen from a 29-0-5 on 5,000 square feet: 1 ÷ 0.29 × 5 = about 17 lb of fertilizer.

How much nitrogen per 1,000 square feet at one time?

K-State says never more than 1 lb of actual nitrogen per 1,000 square feet from a quick-release source in one application, and UConn says no more than 1 lb at one time. K-State allows 2 to 3 lb of slow-release nitrogen, applied less often.

When should I fertilize my lawn?

For cool-season grass, early fall is the one feeding every schedule includes; K-State adds early May and late season, Missouri early November or April–May, UConn late April through May. For warm-season grass, start once it greens up in spring; Missouri says late May and mid-July, K-State monthly during active growth.

What do the three numbers on fertilizer mean?

Nitrogen, phosphate and potash, as a percentage of the bag’s weight. A 29-0-5 is 29% nitrogen, 0% phosphate and 5% potash. Dividing 100 by the first number gives the pounds of product that put down 1 lb of nitrogen.

How many times a year should I fertilize?

It depends on the grass and the state’s guidance. K-State puts Kentucky bluegrass and tall fescue at 2–4 lb of nitrogen a year and Bermuda at 4–8; Clemson puts centipede at ½–2 and warns against more than 2. At 1 lb per application, that is one application per pound.

How much fertilizer does centipede grass need?

Very little. Clemson puts it at 1 to 2 lb of nitrogen per 1,000 square feet a year in the Piedmont and ½ to 2 on the coast, and says more than 2 lb a year often leads to centipedegrass decline. Its example for the Piedmont is ½ to 1 lb in May and again in August.