Calculators for Mixing Water-Soluble Fertilizer

  • student in greenhouse


Sometimes mixing water-soluble fertilizer can be tricky.​ The fertilizer label only gives measurements for a few concentrations and injector settings, and finding the ones in the middle needs some math. Sometimes you know the % nitrogen in the fertilizer, but the label does not give accurate mixing instructions.​ Mixing full bags is always more accurate (and easier) than weighing out fertilizer, but how to do that is not usually on the label.​ Use these calculators for those situations.

To get all of these calculators in a mobile format, click here.

Video Tutorial

How to use Greenhouse Fertilizer Calculators


The results in these calculators refer to “ounces per gallon of stock solution”.  Remember, this is different than adding a certain number of gallons of water (which you should not do!).  When mixing water soluble fertilizer, put less than ½ of the total volume required into the tank, then add the fertilizer, then mix and add water to increase the total volume of stock to the required level.

For calculators to help with Electrical Conductivity (EC), adjusting injector ratios and nitrogen concentration, see this resource.

 Calculator 4:  How many ounces per gallon should I mix?

 Calculator 5:  How many ounces per gallon should I mix if I don’t have mixing instructions, but I know the %N of the fertilizer?  

 Calculator 6:  Into how many gallons of stock should I mix a whole bag? 


Landscape & Greenhouse Field Specialist
Extension Field Specialist, Landscape & Greenhouse
Office: Coop Extension, Taylor Hall, Durham, NH 03824