Fertilizer NPK PPM Calculator
Your feeding chart says "150 PPM nitrogen" but the fertilizer bag says "20-20-20". How many grams go in the tank? This bridges the gap — enter tank volume, target PPM, and the nutrient percentage, and get grams.
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Fertilizer NPK PPM Calculator
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Your feeding chart says "150 PPM nitrogen" but the fertilizer bag says "20-20-20". How many grams go in the tank? This bridges the gap — enter tank volume, target PPM, and the nutrient percentage, and get grams.
How to use this calculator
- Enter tank volume in liters.
- Enter target nitrogen PPM.
- Enter the N percentage of your fertilizer.
- Get grams to weigh out.
The formula
Grams = target PPM × liters ÷ 1,000 ÷ (N% ÷ 100). The division by the nutrient fraction accounts for the rest of the bag being filler.
What the inputs mean
The target is the concentration you want, in PPM. The volume is how much liquid you are treating. The nitrogen content of fertilizer (%) corrects for product strength, because most products are not 100% active ingredient. The result tells you exactly how much fertilizer to add.
Worked example
100 L tank, 150 PPM N, using 20% N fertilizer: 150 × 100 ÷ 1,000 ÷ 0.20 = 75 g.
Quick reference
| Tank | Grams for 150 PPM N (20% fert) |
|---|---|
| 20 L | 15 g |
| 100 L | 75 g |
| 1,000 L | 750 g |
Adjust for your fertilizer's actual N%.
Where you will actually use this
Eyeballing fertilizer burns plants; underdosing starves them. Grams on a scale beat scoops every time.
- Hydroponic reservoirs
- Fertigation dosing
- Greenhouse production
- Home gardening
Mistakes that give wrong answers
- Using the NPK numbers as PPM directly
- Forgetting to divide by the nutrient fraction
- Not dissolving fully before adding plants
Key takeaways
- Formula: Fertilizer (g) = Target N PPM × Volume (L) ÷ 1,000 ÷ N fraction
- Remember: Adjust for your fertilizer's actual N%.
- Watch out for: Using the NPK numbers as PPM directly
- Next step: run your own numbers in the calculator above, then verify with a measurement — calculated values are only as good as the inputs.
Frequently asked questions
How many PPM nitrogen do plants need?
Seedlings 50–100, vegetative 100–200, flowering varies by crop.
What does 20-20-20 mean?
20% nitrogen, 20% phosphate, 20% potash by weight.