Water-Soluble Fertilizer Calculator

The Water-Soluble Fertilizer Calculator tells you exactly how many grams of fertilizer to dissolve in water to hit a precise nutrient concentration — useful for hydroponics, greenhouse feeding, or any situation where nutrient levels need to be controlled. Select your fertilizer type (or enter custom NPK percentages), enter your water volume and water temperature, then choose a target element and target concentration in ppm. You'll get the fertilizer amount required in grams, plus the resulting Nitrogen, Phosphorus, and Potassium ppm levels and Total Dissolved Solids.

L
°F
%
%
%
ppm

Results

Fertilizer Required

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Nitrogen (N) PPM

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Phosphorus (P) PPM

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Potassium (K) PPM

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Total Dissolved Solids

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Frequently Asked Questions

Why mix your own fertilizer solution?

Mixing your own fertilizer solution saves money, allows precise nutrient control, and provides fresher nutrients than pre-mixed solutions. It's especially beneficial for greenhouse growers and hydroponic systems.

What water source should I use for mixing fertilizer?

Use distilled water or reverse osmosis water for best results. Tap water can work but may contain dissolved minerals that affect nutrient ratios and total dissolved solids measurements.

How accurate are PPM calculations for fertilizer mixing?

PPM calculations are quite accurate for major nutrients (N-P-K). However, total dissolved solids will be higher due to minor elements, trace nutrients, and carrier compounds in the fertilizer.

What's the difference between nitrogen PPM and TDS?

Nitrogen PPM measures only the nitrogen content, while TDS (Total Dissolved Solids) includes all dissolved materials including other nutrients, salts, and carrier compounds. TDS is typically 3-5 times higher than nitrogen PPM.

Can I use tablespoons instead of grams to measure fertilizer?

While possible, gram measurements are more accurate. If using tablespoons, note that 1 tablespoon of typical fertilizer weighs approximately 12-15 grams, but this varies by fertilizer density.

What's the maximum safe fertilizer concentration?

Most plants tolerate 200-400 PPM nitrogen. Seedlings need 100-150 PPM, mature plants can handle 300-500 PPM. Always start lower and increase gradually to avoid nutrient burn.

How do I convert P₂O₅ and K₂O to actual P and K?

Fertilizer labels show P₂O₅ and K₂O, not pure P and K. To convert: P = P₂O₅ × 0.436, K = K₂O × 0.83. Our calculator handles this conversion automatically.

Does water temperature affect fertilizer solubility?

Yes, warmer water dissolves fertilizers better. Cold water may not fully dissolve concentrated solutions, leading to precipitation. Use room temperature or slightly warm water for best results.