How do I work out how much fertilizer to put on my lawn?

Divide the pounds of nitrogen you want by the nitrogen fraction on the bag. For 1 lb of N per 1,000 sq ft from a 32-0-4, that is 1 ÷ 0.32 = 3.13 lb of product per 1,000 sq ft. Multiply by the lawn in thousands of square feet: a 5,000 sq ft lawn takes 15.6 lb, which is 2 bags of 15 lb. Penn State Extension teaches the same division with a 26-5-10 (1 ÷ 0.26 = 3.8 lb).

How much nitrogen should I apply at one time?

Extension sources commonly keep a single feeding to 0.5 to 1 lb of nitrogen per 1,000 sq ft. Penn State advises no more than 1 lb of N per 1,000 sq ft per application, UConn no more than 1 lb of water-soluble N, and Texas A&M AgriLife 1 lb or less. Some states write a limit into law (Pennsylvania caps an application at 0.9 lb of total N per 1,000 sq ft). The calculator’s default is 1 lb; lower it to 0.5 or 0.75 for quick-release products, sandy soil or a lawn in heat.

How much nitrogen does a lawn need in a year?

It depends on the grass, the state and how well you want the lawn kept. The extension ranges in the table are about 1 to 4 lb of N per 1,000 sq ft a year for most home lawns, from about 2 lb for cool-season grass with clippings left on up to 2 to 4 lb for bermudagrass and tall fescue in Georgia and 3.5 to 4 lb for a very well-kept Kentucky bluegrass lawn (Purdue). Split the total into several feedings, and ask your local extension office for the schedule that fits your grass and your region. These are guidance, not a rule for your lawn.

What do the three numbers on the bag mean?

They are the percentages by weight of nitrogen (N), phosphate (P2O5) and potash (K2O), in that order. A 15 lb bag of 32-0-4 holds 4.8 lb of N, no phosphate and 0.6 lb of K2O. The phosphorus and potassium are stated as oxides; the elemental amounts are P = P2O5 × 0.436 and K = K2O × 0.83. The calculator shows the pounds of each applied, from the product you spread.

Why would I feed to a phosphate or potash target?

Almost always you do not. Lawns are fed by their nitrogen, and a soil test often shows enough phosphorus. Pick the phosphate or potash target only where a soil test report asks for a pounds-per-1,000-sq-ft amount of one of them. The calculator then sizes the product to that nutrient and shows the nitrogen that comes with it, which can exceed what one feeding should carry (it flags a nitrogen rate above 1 lb).

Are there rules about lawn fertilizer where I live?

Some states and towns limit phosphorus on established lawns, cap the nitrogen per application or per year, and ban spreading in winter, on frozen ground or near water. Always follow the directions and the rate on the product label and check your state agriculture department or extension office for current rules. This calculator works out amounts; it does not check them against any law.

Do I need to add a buffer or extra for waste?

No. The product is spread at the rate worked out from the label, so no waste percentage is added; a calibrated spreader puts it down evenly. The bag count is rounded up to a whole bag, and the result tells you how much will be left in the last one. If you spread by hand or by an uncalibrated spreader, calibrate it on a driveway first rather than adding more product.

Should I fertilize before or after seeding?

A new lawn from seed usually gets a starter fertilizer at seeding, with the rate and phosphorus on that product’s label, and overseeding follows the same plan. See the grass seed calculator for the seed and the sod calculator if you are laying turf. Established lawns are fed on the extension schedule for their grass.

Lawn Fertilizer Calculator: Pounds and Bags for Your Lawn

A 5,000 sq ft lawn fed 1 lb of nitrogen per 1,000 sq ft with a 32-0-4 fertilizer needs 3.13 lb of product per 1,000 sq ft, 15.6 lb in all: 2 bags of 15 lb. That puts down 5 lb of N, no phosphate and 0.6 lb of potash (K2O). Pounds of product per 1,000 sq ft = target lb of N ÷ (% N on the bag ÷ 100). Follow the product label and your state’s rules.

Figures based on the sources listed belowUpdated 2026-10-11How we calculate

Lawn length

Lawn width

Allowance

None: the label rate is the rate (0%)Custom

Extra lawn area (sq ft)

Lawn that is not in the rectangle above, such as a side yard or a strip by the road. Add beds, the house and paving as left-out areas.

Nitrogen, N (%)

Percent nitrogen: the first of the three numbers on the bag, 32 for a 32-0-4. Urea is 46-0-0.

Phosphate, P2O5 (%)

Percent phosphate: the second number on the bag. Many lawn fertilizers carry none, and some states limit phosphorus on established lawns.

Potash, K2O (%)

Percent potash: the third number on the bag.

Feed to a target ofLawns are fed by nitrogen. Pick phosphate or potash only if a soil test asks for one; the nutrient you pick sets the amount of product and the other two come along at the bag’s ratio.

Target rate (lb per 1,000 sq ft)

Pounds of the nutrient picked above, per feeding (1 lb per 1,000 square feet is about 4.9 g per m²). Extension sources commonly advise 0.5 to 1 lb of nitrogen at a time, and no more than 1.

Bag weight (lb)

The net weight printed on the bag, in pounds (2.2 lb to the kilogram).

Price per bag (optional)

Buy 2 bags

5,000 sq ft + 0% waste = 5,000 sq ft

Product per 1,000 sq ft: 3.13 lb of product per 1,000 sq ft (15.3 g per m²)
Total product: 15.6 lb, 14.4 lb left in the bags
Nitrogen (N) applied: 5 lb, 1.00 lb per 1,000 sq ft (4.9 g per m²)
Phosphate (P2O5) applied: 0 lb, 0.00 lb per 1,000 sq ft (0.0 g per m²)
Potash (K2O) applied: 0.6 lb, 0.13 lb per 1,000 sq ft (0.6 g per m²); 0.10 lb per 1,000 sq ft as elemental K

How this number is calculated

5,000 sq ft (no waste added) ÷ 4,800 sq ft per bag = 2 bags

Next step in your project

Grass Seed Calculator
Overseeding first? Grass seed for the same lawn. Opens with your 100 × 50 ft filled in.

Shopping list

Lawn fertilizer (nitrogen, slow-release)
Broadcast spreader
Drop spreader
Soil test kit
Measuring wheel
Garden gloves

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Pounds of fertilizer per 1,000 sq ft by % nitrogen and target rate

Product lb per 1,000 sq ft = target lb N ÷ (% N ÷ 100). Common single-feeding rates are 0.5 to 1 lb of N per 1,000 sq ft; multiply by the lawn in thousands of square feet for the total.
Nitrogen on the bag	0.5 lb N	0.75 lb N	1 lb N
10% N	5 lb	7.5 lb	10 lb
16% N	3.13 lb	4.69 lb	6.25 lb
20% N	2.5 lb	3.75 lb	5 lb
24% N	2.08 lb	3.13 lb	4.17 lb
28% N	1.79 lb	2.68 lb	3.57 lb
32% N	1.56 lb	2.34 lb	3.13 lb
46% N	1.09 lb	1.63 lb	2.17 lb

Bags of 32-0-4 for 1 lb N per 1,000 sq ft by lawn size and bag weight

Worked by this calculator: whole bags, rounded up, no waste added.
Lawn	Product needed	15 lb bags	20 lb bags	40 lb bags	50 lb bags
2,500 sq ft	7.8 lb	1	1	1	1
5,000 sq ft	15.6 lb	2	1	1	1
7,500 sq ft	23.4 lb	2	2	1	1
10,000 sq ft	31.3 lb	3	2	1	1
15,000 sq ft	46.9 lb	4	3	2	1

Annual nitrogen by grass type: extension guidance (not a prescription)

Pounds of N per 1,000 sq ft per year from the university sources listed under Sources. These are ranges that depend on state, how much you want the lawn to look like a golf green, and whether clippings are left on. Divide the year’s total by the 0.5 to 1 lb of a single feeding to count the feedings. Check your own state’s extension office for local timing and amounts.
Grass	Annual N, lb per 1,000 sq ft	Source and notes
Kentucky bluegrass	1 to 2 (low to medium upkeep); 2 to 4 (high upkeep)	Penn State; Purdue puts a very well-kept bluegrass lawn at 3.5 to 4
Cool-season grasses in general (fescues, perennial ryegrass)	About 2, clippings left on the lawn	UConn; up to about 3 if clippings are removed
Tall fescue	2 to 4	University of Georgia; two thirds of a cool-season lawn’s nitrogen goes on in fall (Purdue)
Bermudagrass	2 to 4	University of Georgia; four feedings of about 1 lb each
St. Augustinegrass	2 to 4 (north Florida) up to 4 to 6 (south Florida)	UF/IFAS; Georgia gives 2 to 4
Zoysiagrass	2 to 3 (north Florida) to 2 to 4 (central Florida)	UF/IFAS; editions differ
Bahiagrass	1 to 3	UF/IFAS
Centipedegrass	0.4 to 2 (north Florida)	UF/IFAS; feed lightly, too much can hurt it

Methodology & assumptions

The area to feed is lawn length × width, plus any extra lawn area you enter, minus the areas you leave out (beds, house, driveway), in square feet. The bag’s three numbers are the percentages of nitrogen (N), phosphate (P2O5) and potash (K2O). Pounds of product per 1,000 sq ft = the target pounds of the nutrient ÷ (its percentage ÷ 100): 1 lb of N from a 32-0-4 is 1 ÷ 0.32 = 3.125 lb. Total product = that × area ÷ 1,000, and bags = total product ÷ the bag weight, rounded up. Nothing is added for waste: the rate is the label or extension rate, and a spreader is set to put it down evenly. The nutrients applied are the product spread × each percentage; the P and K on the label are the oxide forms, so elemental P = P2O5 × 0.436 and elemental K = K2O × 0.83. Feeding to a phosphate or potash target is offered for lawns where a soil test calls for one; the amount of product is then set by that nutrient and nitrogen comes along at the bag’s ratio, which can be well over the 1 lb of N per feeding that extension sources advise, and the result says so. The annual nitrogen ranges on the page are guidance from the university sources listed, which differ by state and by how the lawn is kept; they do not set the calculation. Rates are pounds per 1,000 sq ft in either unit system, with grams per m² shown beside them (1 lb per 1,000 sq ft is 4.88 g per m²). Product weights shown in kilograms under the metric toggle.

How to calculate how much lawn fertilizer you need

Measure the lawn. Measure length and width in feet, add any extra lawn areas, and subtract beds, the house, the driveway and other areas that get no fertilizer.
Read the bag. Find the three numbers (N-P-K) and the bag weight. The first number is the percentage of nitrogen.
Choose a target rate. Pick the pounds of nitrogen per 1,000 sq ft for this feeding, commonly 0.5 to 1, following the label and your extension office.
Divide by the nitrogen fraction. Pounds of product per 1,000 sq ft = target pounds of N ÷ (% N ÷ 100).
Scale up and count bags. Multiply by the lawn area in thousands of square feet to get the pounds, divide by the bag weight and round up.

Worked examples

Project	Result
100 × 50 ft lawn, 32-0-4 at 1 lb N per 1,000 sq ft, 15 lb bags	5,000 sq ft → 2 bags of 15 lb (15.6 lb of product)
125 × 80 ft lawn, urea (46-0-0) at 0.75 lb N per 1,000 sq ft, 50 lb bags	10,000 sq ft → 1 bag of 50 lb (16.3 lb of product)
60 × 40 ft lawn, 20-5-10 at 0.5 lb N per 1,000 sq ft, 20 lb bags	2,400 sq ft → 1 bag of 20 lb (6 lb of product, 0.3 lb of P2O5)
100 × 60 ft lot plus a 400 sq ft side yard, less a 40 × 30 ft house, 28-0-3 at 1 lb N, 15 lb bags	5,200 sq ft → 2 bags of 15 lb (18.6 lb of product)
100 × 50 ft lawn fed to a soil-test target of 0.5 lb P2O5 per 1,000 sq ft with 18-24-12 (an illustration of the phosphate option)	5,000 sq ft → 1 bag of 15 lb (10.4 lb of product, 0.38 lb N per 1,000 sq ft comes with it)

Frequently asked questions

How do I work out how much fertilizer to put on my lawn?: Divide the pounds of nitrogen you want by the nitrogen fraction on the bag. For 1 lb of N per 1,000 sq ft from a 32-0-4, that is 1 ÷ 0.32 = 3.13 lb of product per 1,000 sq ft. Multiply by the lawn in thousands of square feet: a 5,000 sq ft lawn takes 15.6 lb, which is 2 bags of 15 lb. Penn State Extension teaches the same division with a 26-5-10 (1 ÷ 0.26 = 3.8 lb).
How much nitrogen should I apply at one time?: Extension sources commonly keep a single feeding to 0.5 to 1 lb of nitrogen per 1,000 sq ft. Penn State advises no more than 1 lb of N per 1,000 sq ft per application, UConn no more than 1 lb of water-soluble N, and Texas A&M AgriLife 1 lb or less. Some states write a limit into law (Pennsylvania caps an application at 0.9 lb of total N per 1,000 sq ft). The calculator’s default is 1 lb; lower it to 0.5 or 0.75 for quick-release products, sandy soil or a lawn in heat.
How much nitrogen does a lawn need in a year?: It depends on the grass, the state and how well you want the lawn kept. The extension ranges in the table are about 1 to 4 lb of N per 1,000 sq ft a year for most home lawns, from about 2 lb for cool-season grass with clippings left on up to 2 to 4 lb for bermudagrass and tall fescue in Georgia and 3.5 to 4 lb for a very well-kept Kentucky bluegrass lawn (Purdue). Split the total into several feedings, and ask your local extension office for the schedule that fits your grass and your region. These are guidance, not a rule for your lawn.
What do the three numbers on the bag mean?: They are the percentages by weight of nitrogen (N), phosphate (P2O5) and potash (K2O), in that order. A 15 lb bag of 32-0-4 holds 4.8 lb of N, no phosphate and 0.6 lb of K2O. The phosphorus and potassium are stated as oxides; the elemental amounts are P = P2O5 × 0.436 and K = K2O × 0.83. The calculator shows the pounds of each applied, from the product you spread.
Why would I feed to a phosphate or potash target?: Almost always you do not. Lawns are fed by their nitrogen, and a soil test often shows enough phosphorus. Pick the phosphate or potash target only where a soil test report asks for a pounds-per-1,000-sq-ft amount of one of them. The calculator then sizes the product to that nutrient and shows the nitrogen that comes with it, which can exceed what one feeding should carry (it flags a nitrogen rate above 1 lb).
Are there rules about lawn fertilizer where I live?: Some states and towns limit phosphorus on established lawns, cap the nitrogen per application or per year, and ban spreading in winter, on frozen ground or near water. Always follow the directions and the rate on the product label and check your state agriculture department or extension office for current rules. This calculator works out amounts; it does not check them against any law.
Do I need to add a buffer or extra for waste?: No. The product is spread at the rate worked out from the label, so no waste percentage is added; a calibrated spreader puts it down evenly. The bag count is rounded up to a whole bag, and the result tells you how much will be left in the last one. If you spread by hand or by an uncalibrated spreader, calibrate it on a driveway first rather than adding more product.
Should I fertilize before or after seeding?: A new lawn from seed usually gets a starter fertilizer at seeding, with the rate and phosphorus on that product’s label, and overseeding follows the same plan. See the grass seed calculator for the seed and the sod calculator if you are laying turf. Established lawns are fed on the extension schedule for their grass.