Fertilizer Calculator

This fertilizer calculator works out how much lawn fertilizer to spread to deliver a set amount of nitrogen. Enter your lawn area, the three N-P-K numbers from the bag and the pounds of nitrogen you want per 1,000 square feet, and it returns the product rate, the total amount to buy and the number of bags.

Lawn feeding advice is almost always given in pounds of actual nitrogen, not pounds of product, which is why a 46-0-0 and a 10-10-10 need very different amounts. The default target is 1 lb of nitrogen per 1,000 sq ft, a common single feeding. Your fertilizer label and any local rules always come first.

How to Use the Fertilizer Calculator

1
Enter the lawn area
Choose US or Metric, then type the total area or switch to Length × width and enter the dimensions.
2
Enter the N-P-K numbers
Copy the three numbers from the fertilizer bag into the N %, P % and K % boxes, for example 24, 0 and 6.
3
Set the nitrogen target
Leave the target at 1 lb of nitrogen per 1,000 sq ft or lower it, for example to 0.5 for a light or quick-release feeding.
4
Add the bag weight and read the results
Enter the net weight of one bag to see how many bags you need. The results show product per 1,000 sq ft, total product, nitrogen applied and the phosphate and potash that come with it.

How the fertilizer calculator works

The first number on a fertilizer bag is the percentage of nitrogen by weight. A 24-0-6 product is 24% nitrogen, so each pound of product contains 0.24 lb of nitrogen. To apply 1 lb of nitrogen, you divide 1 by 0.24 and get 4.17 lb of product per 1,000 sq ft.

The calculator then scales that rate to your lawn size and divides by the bag weight. It also multiplies the product rate by the P and K percentages to show the phosphate (P2O5) and potash (K2O) you apply at the same time. In metric mode the target is in grams of nitrogen per square meter, where 4.9 g/m² is about 1 lb per 1,000 sq ft.

Product per 1,000 sq ft = target N ÷ (N% ÷ 100)
Total product = product per 1,000 sq ft × area ÷ 1,000
Bags = total product ÷ bag weight, rounded up
P2O5 or K2O applied = product × P% or K% ÷ 100

Worked example: 5,000 sq ft with 24-0-6

The same lawn fed with a 10-10-10 product needs 10 lb per 1,000 sq ft, or 50 lb in total, to supply the same 1 lb of nitrogen. It also applies 1 lb of phosphate per 1,000 sq ft, which many lawns do not need.

Target: 1 lb of nitrogen per 1,000 sq ft.
Product rate: 1 ÷ 0.24 = 4.17 lb of 24-0-6 per 1,000 sq ft.
Total product: 4.17 × 5,000 ÷ 1,000 = 20.8 lb (9.45 kg).
Nitrogen applied: 20.8 × 0.24 = 5 lb across the whole lawn.
Potash: 4.17 × 0.06 = 0.25 lb of K2O per 1,000 sq ft.
Bags: with a 50 lb bag, 20.8 ÷ 50 = 0.42, so one bag covers it with plenty left over.

Product needed per 1,000 sq ft by nitrogen content

Pounds of product per 1,000 sq ft to apply the nitrogen shown in each column. Multiply by your area in thousands of square feet for the total.

Nitrogen (first number)	0.5 lb N	0.75 lb N	1 lb N
46% (e.g. 46-0-0)	1.09 lb	1.63 lb	2.17 lb
32% (e.g. 32-0-4)	1.56 lb	2.34 lb	3.13 lb
29% (e.g. 29-0-4)	1.72 lb	2.59 lb	3.45 lb
24% (e.g. 24-0-6)	2.08 lb	3.13 lb	4.17 lb
21% (e.g. 21-0-0)	2.38 lb	3.57 lb	4.76 lb
16% (e.g. 16-4-8)	3.13 lb	4.69 lb	6.25 lb
10% (e.g. 10-10-10)	5 lb	7.5 lb	10 lb
5% (e.g. 5-3-2 organic)	10 lb	15 lb	20 lb

Tips and common mistakes

Calculate from nitrogen, not from product weight. Two bags that both cover 5,000 sq ft can deliver very different amounts of nitrogen.
Most extension guidance keeps a single feeding at or below about 1 lb of nitrogen per 1,000 sq ft, and often 0.5 lb for quick-release products. The calculator warns you if you go above 1 lb.
The number of feedings per year depends on your grass type, climate and whether you return clippings. Local extension services publish yearly schedules for common lawn grasses.
Get a soil test before adding phosphorus or potassium. Many lawns already have enough, and many areas restrict phosphorus on established lawns.
Calibrate your spreader and follow the setting on the bag. The calculator tells you how much to buy; the spreader setting controls how evenly it goes down.

Label rates, local rules and runoff

The application rate and directions on the fertilizer label take priority over this calculator. The label is written for that exact product, its release rate and its spreader settings.

Many states, counties and towns regulate lawn fertilizer: limits on phosphorus, buffer zones near lakes and streams, seasonal blackout dates and bans on applying to frozen ground or before heavy rain. Check the rules where you live. Sweep any granules off driveways, sidewalks and streets back onto the lawn so they do not wash into storm drains.

Features

Works from the N-P-K analysis on any fertilizer bag
Target nitrogen per application (default 1 lb per 1,000 sq ft)
Product per 1,000 sq ft, total pounds or kilograms, and bags
Shows the phosphate and potash applied at the same rate
Area by total or length × width, in US or metric units

Frequently Asked Questions

How do I calculate how much fertilizer to use?

Divide the pounds of nitrogen you want per 1,000 sq ft by the nitrogen percentage as a decimal. For 1 lb of nitrogen with a 24-0-6 fertilizer, that is 1 ÷ 0.24 = 4.17 lb of product per 1,000 sq ft. Multiply by your lawn area in thousands of square feet: a 5,000 sq ft lawn needs 20.8 lb.

How much nitrogen should I put on my lawn?

A common single feeding is 0.5 to 1 lb of actual nitrogen per 1,000 sq ft, and many extension services advise not exceeding about 1 lb in one application. How many feedings a year you need depends on grass type, climate and soil. Follow the fertilizer label and local extension guidance for your lawn.

What do the three numbers on a fertilizer bag mean?

They are the N-P-K analysis: the percentage by weight of nitrogen (N), phosphate (P2O5) and potash (K2O). A 50 lb bag of 24-0-6 contains 12 lb of nitrogen, no phosphate and 3 lb of potash. The rest is filler, coating and other ingredients that help the product spread evenly.

How much 46-0-0 urea do I need per 1,000 square feet?

To apply 1 lb of nitrogen per 1,000 sq ft, use 1 ÷ 0.46 = 2.17 lb of 46-0-0. For a lighter 0.5 lb feeding, use 1.09 lb. Urea is a quick-release, high-nitrogen product, so lighter rates, even spreading and watering it in as the label directs help reduce the risk of burning the grass.

How much 10-10-10 fertilizer do I need for my lawn?

Because 10-10-10 is only 10% nitrogen, you need 10 lb of product per 1,000 sq ft to apply 1 lb of nitrogen. A 5,000 sq ft lawn would need 50 lb. That rate also applies 1 lb of phosphate and 1 lb of potash per 1,000 sq ft, so check a soil test and local phosphorus rules before using it.

How many bags of fertilizer do I need?

Divide the total product by the net weight of one bag and round up. For example, 5,000 sq ft of 10-10-10 at 1 lb of nitrogen needs 50 lb of product. With 40 lb bags that is 1.25 bags, so you would buy 2. Enter your bag weight in the calculator to get the count directly.

Last reviewed September 21, 2026