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Liquid Fertilizer Dilution Calculator

Enter your water volume and dilution rate to get the concentrate needed.

How it is calculated

Enter the volume of water in litres and the label's dilution rate in millilitres of concentrate per litre of water. The tool computes concentrate (mL) = water (L) × rate (mL/L). The total volume of finished solution is water + concentrate ÷ 1000 litres, because the concentrate is added on top of the water. The ratio is 1 : (water in mL ÷ concentrate in mL), meaning 1 part concentrate to that many parts of water. Both inputs must be above zero. The tool does not convert from tablespoons or gallons, so change the label's rate to mL per litre first.

Worked example

You want to mix 10 L of feed and the bottle says 5 mL per litre. Concentrate: 10 × 5 = 50.0 mL. The final volume is 10 + 50 ÷ 1000 = 10.05 L, a little more than the water alone. The ratio is 10,000 mL of water ÷ 50 mL = 200, written 1 : 200.0. So measure 50 mL of concentrate into a watering can, then fill with water to about 10 L. A smaller 2 L can at the same rate would need 10 mL.

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Common mistakes

  • Typing the label's rate in the wrong unit, such as 1 tablespoon per gallon, as 1 or 15. The field is mL per litre; convert first (1 US gallon is about 3.785 L).
  • Entering the water volume in gallons or millilitres. It must be litres, so 500 mL of water is 0.5.
  • Reading the ratio as parts of concentrate to total solution. The 1 : 200.0 means 1 part concentrate to 200 parts water, so the concentrate is about 0.5% of the finished mixture.
  • Measuring tiny doses by eye. For a 1 L jug at 5 mL per litre the dose is only 5.0 mL, so use a syringe or measuring cup marked in mL rather than a spoon.
  • Assuming stronger is better. Over-strong mixes can burn roots; use the rate printed on the label for your plant and growth stage.

About this calculator

Concentrated liquid fertilizers — fish emulsion, kelp extract, synthetic blends like 20-20-20 — are almost never applied at full strength. The label gives a dilution rate (e.g. “1 tbsp per gallon” or “5 mL per liter”) that balances nutrient delivery against the risk of burning roots with too-strong a solution.

This calculator scales that ratio to whatever volume of water you're actually mixing, whether it's a 1-liter watering can or a 50-gallon sprayer tank. It's a practical tool for home gardeners, hydroponic growers, and greenhouse operators who need consistent, correctly diluted feed solutions without doing the ratio math by hand every time they mix a batch.

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Comments (1)

  • Editorial team

    Labels often give a rate per gallon or per teaspoon, but this tool wants millilitres per litre. For a per-gallon rate, divide by 3.785 first. For example, 3.785 L of water at 2.5 mL per litre needs 9.5 mL of concentrate. The ratio line then reads 1 : 400, a quick check against a label that states a ratio. Which label unit do you find hardest to convert?

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