How to Weigh Fertilizer

This guide is for you whether this is your first lawn project or you have years of gardening experience. Throughout this guide, we’ll explain: 

  • What is Fertilizer?
  • How to Weigh Fertilizer
  • Benefits of Using Fertilizer
  • How to Determine Nitrogen in a Fertilizer
  • Why is Phosphorus Important?
  • Why is Potassium Important?
  • NPK Analysis 
  • Measuring Fertilizer Application

What is Fertilizer?

Fertilizer is any material used to promote soil growth. There are a myriad of fertilizer varieties, but most store fertilizers follow the N-P-K ratio. Fertilizers are used to keep lawns clean and yield more crops on their fields. 

  • Organic Fertilizers: Organic fertilizers are made of animal or plant matter. 
  • Mineral Fertilizers: These fertilizers are mined and chemically treated before being used. 
  • Industrial Fertilizers: Industrial fertilizers are produced by human chemical reactions. 

While mineral and organic fertilizers are known to increase crop yields, industrial fertilizers are a new development. In modern applications, industrial fertilizers are more used because they produce faster results. 

How to Weigh Fertilizer

Here’s a general rule of thumb. When using the fertilizer, the quality is based on the spreader used to spread the material and the lawn’s square footage. When calibrating the fertilizer, place a 50-pound bag throughout the lawn. 

You can use a kitchen scale to weigh out the fertilizer and apply its sq-ft coverage around your field. Use a spreader to indicate how many fertilizer pounds you’ve added. By weighing your fertilizer, you’ll have an accurate measurement of how much you can spread throughout your property. 

Benefits of Using Fertilizer

With fertilizer, we can help create food faster to sustain the current population. Micronutrient fertilizers are made to give your crops the nutrients they need to improve human health. Here are some reasons why fertilizer is useful for your home lawn:

  • Enhances Microbes

When using organic fertilizer, they contain organic matter that helps with growth and enhancing the microbes. In addition, it contains nitrogen, potassium, and phosphorus that enables the plants to grow throughout the biological process. 

  • Reduced Pesticides

Organic fertilizer has fewer pesticides in comparison to synthetic fertilizer. While it is often more expensive, organic fertilizer will save your crops in the long run. Through its reduced pesticides, it requires less maintenance on your part. 

  • Environmentally Friendly

You’ll want to avoid using synthetic fertilizer if you’re trying to improve the quality of your lawn. In fact, the Organic Trade Organization discovered that organic fertilizer increases biodiversity by 70% in comparison to synthetic fertilizer. 

Once you’ve successfully weighed your fertilizer, you can decide on how to spread it around your garden. 

How to Determine Nitrogen in a Fertilizer

When buying fertilizer, the nitrogen content is the first number on the bag. To determine the nitrogen inside the fertilizer, calculate the nitrogen (lbs) per 1,000 square feet. 

How do you determine the pounds of nitrogen? Start by multiplying the bag’s weight by the nitrogen percentage. This calculation will help tell you how many pounds of nitrogen are stored in the bag. 

Next, divide the nitrogen pounds by the approximate space the fertilizer will cover. Most fertilizer products come with a 5,000 square Ft or 10,000 square Ft of coverage. 

For example, let’s say you have a 48 lb fertilizer bag with an NPK analysis of 28-4-13. The bag covers over 10,000 square. Ft, so how would you calculate this?

48 lbs x (28/100) = 13.44 lbs of nitrogen in the bag. 

13.44 lbs of nitrogen / 10,00 squ. Ft = 0.013 lbs of nitrogen per squ. Ft.

Why is Phosphorus Important?

Phosphorus is the middle number on the NPK analysis. The nutrient is used for root growth, fruiting, and blooming, making it extremely useful for plants growing in the spring.  

In addition, phosphorus is useful for fundamental plant growth, such as setting flower buds and rooting. 

Why is Potassium Important? 

 Potassium is the final number listed on the NPK analysis. For plants, potassium helps with strengthening the plant’s immune system and its ability to resist disease. This is useful for plants growing in dry or cold areas as it allows them to last longer. 

NPK Analysis 

NPK analysis is a term used to measure the nitrogen, phosphorus, and potassium content within a fertilizer. When looking at fertilizer products, the NPK analysis is marked by three numbers separated by dashes. 

For instance, let’s say you purchased a fertilizer bag with the numbers “10-5-6”. This means it has 10% nitrogen, 5% phosphorous, and 6% potassium. The remaining 79% of the bag is made of files or minor nutrients. 

Knowing your fertilizer’s NPK values can help with finding one that’s appropriate to the plant you’re attempting to grow. For instance, if you’re trying to grow vegetables, you’re going to want a fertilizer that has a higher nitrogen concentration. 

There are balanced or complete fertilizer packages available. For instance, a fertilizer with the NPK ratio of “30-30-30” would be considered balanced because all of their numbers are aligned.  However, an NPK ratio of “10-30-0” would be an incomplete fertilizer. Both are useful based on the NPK concentration on your lawn. 

Measuring Fertilizer Application Rate

The fertilizer application rate is dependent on your plant’s nutrient needs and the formula. Nitrogen is the most important nutrient as it determines its growth and utilizes the chlorophyll within the plant. 

Start a soil test to measure the potassium and phosphorus within the fertilizer. Most soils have an ample amount of these components, so you don’t have to add too much.  Giving your soil too much of these nutrients will lead to increased salt levels within the soil. 

How much fertilizer will you need for a large area? Determine the square feet of the area and divide that by the recommended amount of nutrients of the plant by the recommended amount of nutrients for the fertilizer. 


While weighing fertilizer appears complicated, it is the best way to utilize space on your lawn. Find the NPK ratio that works best with your soil and spread it evenly. By doing this, you’ll utilize your garden and give it the nutrients needed for long-term growth. 

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