How the calculation works

The three numbers on a fertilizer bag are percentages by weight of nitrogen (N), phosphate (P₂O₅) and potash (K₂O). A bag of 24-0-6 is 24% nitrogen, no phosphate and 6% potash.

Product per 1,000 sq ft = target pounds of nitrogen ÷ (N% ÷ 100). This is the method Purdue and Penn State Extension teach.
Total for the lawn = product per 1,000 sq ft × lawn area ÷ 1,000.
Bags: the total ÷ bag size, rounded up to whole bags. One bag covers bag weight ÷ product per 1,000 sq ft × 1,000 sq ft.
Phosphate and potash = product per 1,000 sq ft × P% ÷ 100 (or K% ÷ 100).
Metric: the same formula with grams of nitrogen per square metre. 1 lb per 1,000 sq ft equals 4.88 g/m².

Worked example

A 100 × 50 ft lawn is 5,000 sq ft. You have 50 lb bags of 24-0-6 and want 1 lb of nitrogen per 1,000 sq ft.

Product per 1,000 sq ft: 1 ÷ 0.24 = 4.17 lb.
For the whole lawn: 1 ÷ 0.24 × 5 = 20.8 lb. One 50 lb bag is enough, with 29.2 lb left over. At this rate a bag covers 12,000 sq ft.
Along with 5 lb of nitrogen, it puts down 4.17 × 0.06 = 0.25 lb of potash per 1,000 sq ft (1.25 lb across the lawn) and no phosphate.

In metric, a 500 m² lawn fed 4.9 g of nitrogen per m² with 24-0-6 needs 4.9 ÷ 0.24 = 20.4 g of product per m², or 10.2 kg in total. A 20 kg bag covers 980 m² at that rate. It also supplies 1.2 g of potash per m² and 2.45 kg of nitrogen across the lawn.

How much nitrogen in one application?

Extension guides agree on about 1 lb of nitrogen per 1,000 sq ft (4.9 g/m²) or less per feeding; NC State Extension calls 1 lb a typical lawn feeding. They differ in the detail:

Purdue Extension normally aims for 0.5 to 1.0 lb (2.4 to 4.9 g/m²). It says to apply no more than 1.0 lb of water-soluble nitrogen at once, or up to 2.0 lb (9.8 g/m²) when more than half the nitrogen is slow-release. The label shows how much is slow-release; it may be called controlled-release or water-insoluble nitrogen.
Penn State's soil testing lab suggests 0.75 to 1.0 lb (3.7 to 4.9 g/m²) per application and no more than 1 lb.
Texas A&M AgriLife Extension says to split the year's nitrogen into applications of 1 lb or less.
Pennsylvania law is stricter: no more than 0.7 lb of plant-available nitrogen per 1,000 sq ft (3.4 g/m²) per application, and no more than 0.9 lb of total nitrogen (4.4 g/m²) unless the product is an enhanced-efficiency fertilizer.

The calculator warns you when your target is above Purdue's limits. If the product label gives a lower rate, follow the label.

How much nitrogen in a year?

The yearly total depends on your grass and how much care you give the lawn. NC State Extension says many lawns do fine on 1 or 2 lb per 1,000 sq ft a year. Divide the yearly total by your rate per application to see how many feedings that is. For metric, multiply the figures below by 4.88 to get grams per m².

Cool-season grasses

Purdue Extension gives 1 to 5 lb a year for mature cool-season lawns: 1 to 3 lb for the lowest-maintenance lawns and 3 to 5 lb for the most intensively kept, regularly watered ones. Shaded lawns should get no more than 2 lb a year. Penn State's figures by grass are below.

Grass	Low to medium care	High care
Kentucky bluegrass	1–2	2–4
Perennial ryegrass	1–2	2–4
Tall fescue	1–2	2–3
Fine fescues	1	2

Pounds of nitrogen per 1,000 sq ft per year. Source: Penn State Agricultural Analytical Services Laboratory. NC State's yearly schedule uses 2 lb for tall fescue and Kentucky bluegrass, and 3 lb for Kentucky bluegrass mixed with perennial ryegrass.

Penn State says the lower rates suit lawns more than 4 years old on good soil, with light traffic and clippings left on the lawn. New lawns, poor soils, heavy traffic and lawns where clippings are removed benefit from the higher rates.

Warm-season grasses

Grass	Low care	Moderate	High care
Bermudagrass (common)	2	2–3	4–5
Bermudagrass (hybrid)	2	3–4	5–6
Zoysiagrass	1–2	2–3	3–4
St. Augustinegrass, sun	2	2–3	3–4
St. Augustinegrass, shade	1	1–2	Not recommended
Centipedegrass	0–1	1–2	Not recommended
Buffalograss	0–1	2	Not recommended

Pounds of nitrogen per 1,000 sq ft per year. Source: Texas A&M AgriLife Extension. NC State's schedule uses 3 lb for bermudagrass and 2 lb for zoysiagrass and St. Augustinegrass.

These figures differ between universities, so if your own state's extension service publishes a schedule for your grass, use that.

When to fertilize

Cool-season lawns (bluegrass, ryegrass, fescues): Purdue advises putting most of the year's nitrogen on from late summer through autumn, less during the spring flush of growth, and little or none in summer unless you water often or remove the clippings.
Warm-season lawns (bermuda, zoysia, St. Augustine, centipede): Texas A&M advises the first feeding after you have mowed the grass (not the weeds) twice, usually about 6 weeks after the average last spring frost. Space any extra summer feedings at least 45 to 60 days apart, and make the last one no later than 6 weeks before the average first autumn frost.
Don't feed a dormant lawn. Purdue and NC State both advise against fertilizing dormant turf or frozen ground, and Purdue adds severely drought-stressed turf. Pennsylvania's rules forbid spreading on frozen or snow-covered ground.

Keep it on the grass

Fertilizer left on sidewalks, driveways or roads can wash away. Sweep or blow it back onto the lawn (Purdue), and don't sweep it into a storm drain (NC State). Minnesota's law requires this clean-up straight away for every kind of fertilizer, and Pennsylvania's rules say not to spread fertilizer on paved surfaces at all.

Phosphorus: check your state's rules

The middle number is phosphate. A soil test is the way to find out whether your lawn needs phosphate or potash (Purdue, Penn State). Some states restrict phosphorus on lawns:

Minnesota bans phosphorus fertilizer on lawns unless a soil or plant tissue test shows a need, or you are starting a new lawn from seed or sod (golf courses and sod farms have their own exceptions). A 0 as the middle number means the product is phosphorus-free. The Minnesota Department of Agriculture notes that ten other states had similar laws by 2012.
Pennsylvania allows no phosphate unless you are establishing, re-establishing or repairing a lawn, with a small allowance for some enhanced-efficiency and organic products.

Rules vary from state to state, so check yours before you buy. The results above show how much phosphate your product would apply.

Outside the US

UK fertiliser packs list nitrogen, phosphorus and potassium as percentages too. The Royal Horticultural Society explains that phosphorus and potassium are usually given as oxides (P₂O₅ and K₂O), followed in brackets by the figure for the element alone. Enter the oxide figures: those are what US bags show and what this calculator expects. Switch to metric to work in m², g/m² and kg.

This calculator only works out plant nutrients. If your product also contains weed or insect control, follow its label for rate and timing.

Common questions

How much fertilizer do I need for 1 lb of nitrogen per 1,000 sq ft?: Divide 100 by the first number on the bag. For 24-0-6 that is 100 ÷ 24 = 4.17 lb of product per 1,000 sq ft. A 10-10-10 fertilizer needs 10 lb, and urea (46-0-0) needs 2.17 lb. For a different target, scale it: half a pound of nitrogen from 24-0-6 takes 2.08 lb of product.
How many square feet does one bag cover?: Multiply the bag weight by the nitrogen percentage as a decimal (24% is 0.24), divide by your nitrogen target and multiply by 1,000. A 50 lb bag of 24-0-6 covers 12,000 sq ft at 1 lb of nitrogen per 1,000 sq ft, or 16,000 sq ft at 0.75 lb. A 50 lb bag of 26-5-10 covers 13,000 sq ft at 1 lb. The calculator shows this as "covered by one bag".
What do the second and third numbers do?: They are the percentages of phosphate (P₂O₅) and potash (K₂O), and you apply them whether your lawn needs them or not. Spreading 26-5-10 at 1 lb of nitrogen per 1,000 sq ft takes 3.85 lb of product, which also puts down 0.19 lb of phosphate and 0.38 lb of potash. A soil test tells you whether your lawn needs either.
What is 1 lb per 1,000 sq ft in metric?: It is 4.88 g of nitrogen per square metre. The calculator rounds this to 4.9 g/m² as its metric starting point. With 24-0-6 you would spread 4.17 lb of product per 1,000 sq ft, which is 20.3 g per m².
How do I measure a lawn that isn't a rectangle?: Split it into simple sections, measure each one and add the areas together, as Texas A&M AgriLife Extension suggests. Leave out the house, drive, deck and planted beds. The length × width boxes work out one rectangle at a time (a right-angled triangle is half of its length × width), so add up the pieces and type the total into the lawn area box.

Sources

Last checked and updated: October 31, 2026.