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Hydroponic Nutrient Calculator

Enter reservoir volume and dose rate to get the nutrient amount per part.

How it is calculated

The dose for one part is per part (mL) = volume (L) × rate (mL/L). The rate is the figure from the nutrient label, in millilitres per litre, and it is applied to each of the two parts separately. The tool then doubles the amount to give the combined A + B total, and also converts the reservoir to US gallons with gallons = litres / 3.785411784. Volume must be above zero and the rate cannot be negative. The tool only multiplies; it does not know your nutrient brand, growth stage or water hardness, so take the rate from the label and check the final strength with an EC or PPM meter.

Worked example

A reservoir holds 60 L and the label says 2.5 mL per litre for each part. Each part is 60 × 2.5 = 150 mL, which the tool shows as 150.00 mL. Parts A and B together are 150 × 2 = 300 mL (300.00 mL). The reservoir is 60 / 3.785 ≈ 15.85 gal.

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Common mistakes

  • Entering a per-gallon dose rate. The field is millilitres per litre; a label value of 2.5 mL per gallon is only about 0.66 mL per litre.
  • Reading the total as the dose of one bottle. The total is A and B together; you measure the per-part amount from each bottle separately.
  • Mixing Part A and Part B together in concentrated form. Add them to the water one after the other, with mixing in between.
  • Entering the volume of water you plan to top up with instead of the full reservoir volume.
  • Treating the result as a final recipe. Check the actual strength with an EC or PPM meter.

About this calculator

Two-part hydroponic nutrients (a “Part A” and “Part B” that must be added separately to avoid precipitating in concentrated form) are dosed by multiplying the reservoir volume by the manufacturer's recommended dose rate per liter or gallon — for example, brands like General Hydroponics' Flora series typically call for roughly 2–3 mL per gallon of each part during the seedling stage, rising to around 8–10 mL per gallon during bloom.

This calculator scales that dose rate to your specific reservoir size and returns the milliliters of each part to add. You enter the reservoir volume in liters and the dose in mL per liter; if your label gives mL per gallon, divide it by 3.785 first. The reservoir size is also shown in gallons. Hydroponic and soilless growers — from hobbyist indoor gardeners to commercial greenhouse operators — use it whenever they mix a new reservoir batch, then typically confirm the resulting nutrient strength with an EC (electrical conductivity) or PPM (parts-per-million) meter before dosing plants.

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