What This Calculator Does
The Water Soluble Fertilizer Calculator tells you exactly how many grams of a powdered or liquid fertilizer to dissolve in a known volume of water to reach a target nitrogen concentration measured in parts per million (ppm). It is widely used in hydroponics, greenhouse fertigation, and container nursery production where nutrient strength is dosed by ppm rather than by guesswork.
How to Use It
Enter three values: the target nitrogen concentration in ppm N, the volume of water you are mixing in liters, and the nitrogen percentage (%N) printed on your fertilizer label — the first number of the N-P-K analysis. The calculator returns the grams of fertilizer to weigh out, plus the resulting concentration in grams per liter so you can scale a stock solution.
The Formula Explained
The core equation is $$\text{Fertilizer (g)} = \dfrac{\text{ppm N} \times \text{Volume (L)}}{\%\text{N} \times 10}$$. Because 1 ppm equals 1 mg per liter, the target mass of nitrogen in milligrams is \(\text{ppm} \times \text{liters}\). Dividing by the nitrogen fraction (\(\%\text{N} / 100\)) converts nitrogen mass to fertilizer mass, and dividing the result by 1000 converts milligrams to grams — together these factors simplify to dividing by (\(\%\text{N} \times 10\)).
Worked Example
Suppose you want 150 ppm N in 100 liters of water using a 20-20-20 fertilizer (20% N). Plug in: $$\frac{150 \times 100}{20 \times 10} = \frac{15000}{200} = \textbf{75 grams}.$$ That gives a concentration of \(0.75 \text{ g/L}\).
FAQ
What is ppm? Parts per million; for water, 1 ppm equals 1 milligram of nutrient per liter of solution.
Which percentage do I enter? Use the nitrogen percentage — the first number of the N-P-K grade (e.g. 20 for 20-20-20).
Can I use gallons? This tool uses liters. Multiply gallons by 3.785 to convert to liters first.
