How to Calculate Liquid Fertilizer


Fertilizer is utilized to replenish the nutrients used by plants as they grow. If the nutrients in your garden soil are depleted at a greater rate than they are replaced, the soil loses its fertility and plants will not grow. Fertilizers are applied in either a liquid or granular form. Liquid fertilizers are applied according to gallons per acre. Applying too much fertilizer causes dangerous runoff that pollutes water and will cause burning of the plants. Correct calculation is essential for a healthy garden.

Step 1

Perform a soil test on your growing area using a soil analysis test according to the packaging instructions, or send a soil sample off to a local university extension. University extensions will provide instructions for the soil collection. This determines the nutrient needs of the soil.

Step 2

Find the nitrogen, phosphorous and potassium content of the material from the fertilizer packaging. Locate the density rating for the fertilizer on the packaging label.

Step 3

Measure the area that you will apply the fertilizer to in acres. One acre is 4,840 square feet.

Step 4

Multiply the percentage of nitrogen by the weight of the fertilizer to determine the weight content of the nitrogen. A 10.86 pounds per gallon amount of fertilizer that has a 30 percent content of nitrogen equals 3.26 pounds of nitrogen per gallon. (10.86 X .30 = 3.26 pounds)

Step 5

Apply the nitrogen to the area according to the nitrogen needs per acre indicated in the soil analysis test.

Things You'll Need

  • Tape measure or measuring device
  • Soil test


  • Virginia Cooperative Extension: Fertilizer Types and Ca
  • Purdue University: Fertilizer Reckoning for the Mathematically Challenged
Keywords: Liquid fertilizer, Calculate liquid fertilizer, Applying liquid fertilizer

About this Author

Cleveland Van Cecil is a freelancer writer specializing in technology. He has been a freelance writer for three years and has published extensively on, writing articles on subjects as diverse as boat motors and hydroponic gardening. Van Cecil has a Bachelor of Arts in liberal arts from Baldwin-Wallace College.