Liquid Fertilizer Dilution Calculator
Liquid and water-soluble fertilizers are mixed by rate, “1 tablespoon per gallon”, but your watering can or sprayer is rarely exactly one gallon. Scale the label rate to any volume, or mix precisely to a target ppm.
View formula
How to use the Liquid Fertilizer Dilution Calculator
- Choose a method: scale the label rate, or mix to a ppm target.
- For label scaling, enter the label rate and the amount of water you are mixing.
- For ppm, enter the target, the fertilizer’s %N and the water volume.
- Press Calculate for the amount in several units.
Scaling a label rate
Label: 1 tbsp per gallon. Your watering can holds 2 gallons: 1 × 2 ÷ 1 = 2 tbsp (about 29.6 ml). For a 1-litre spray bottle: 1 × 1 ÷ 3.785 = 0.26 tbsp ≈ 0.8 tsp.
Mixing to a target ppm
Parts per million (ppm) of nitrogen is how greenhouses and hydroponic growers specify feed strength. Because 1 ppm equals 1 milligram per litre:
To make 150 ppm N in 1 gallon (3.785 L) with a 20-20-20 soluble fertilizer: 150 × 3.785 ÷ (20 × 10) = 2.84 g.
Handy conversions
| Unit | Millilitres |
|---|---|
| 1 teaspoon | 4.93 ml |
| 1 tablespoon (3 tsp) | 14.79 ml |
| 1 fluid ounce (2 tbsp) | 29.57 ml |
| 1 cup (8 fl oz) | 236.6 ml |
| 1 US gallon | 3,785 ml |
Always follow the product label; many growers feed seedlings and houseplants at half strength more often rather than full strength occasionally.
FAQ
Liquid Fertilizer Dilution Calculator: frequently asked questions
How do I convert a per-gallon rate to litres?
Divide the per-gallon amount by 3.785 to get the amount per litre. 1 tbsp per gallon ≈ 0.26 tbsp (3.9 ml) per litre.
What does ppm mean for fertilizer?
Parts per million of a nutrient in the solution, 1 ppm is 1 mg per litre. Recipes often specify ppm of nitrogen.
Can I convert grams to teaspoons?
Only if you know the product’s density, which varies. Weighing powders is more accurate than measuring by spoon.
Is it safe to mix stronger than the label?
No, concentrated fertilizer can burn roots and leaves. If unsure, mix weaker rather than stronger.
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