A hydroponic nutrient calculator that converts your reservoir volume and EC target into precise gram weights for every salt in the recipe — from the macro carriers (calcium nitrate, potassium nitrate, monopotassium phosphate, Epsom salt) to the micronutrient trace elements (manganese sulfate, boric acid, zinc sulfate, copper sulfate, sodium molybdate). Four crop profiles are built in — General Purpose, Leafy Greens, Fruiting and Seedling — each pre-loaded with the elemental targets recommended for that growth stage.
How it works
The calculator is built on the Modified Hoagland nutrient solution (Hoagland and Arnon, 1950), the most widely used reference formula in hydroponic science. For each fertiliser salt it applies a single mass-balance equation:
mass (g) = ( target_ppm × volume_L × MW_salt ) ÷ ( n × AW_element × 1000 )
where target_ppm is the desired milligrams of that element per litre,
volume_L is your reservoir size, MW_salt is the molar mass of the compound
(e.g. 236.15 g/mol for calcium nitrate tetrahydrate), n is how many atoms of
that element appear in one formula unit, AW_element is the element’s atomic weight, and
dividing by 1000 converts mg into grams.
Macro nutrients are allocated to salts in a practical sequence. Calcium nitrate handles all the calcium demand and a proportion of nitrate-nitrogen. Potassium nitrate covers the remaining nitrate-nitrogen while also contributing potassium. Monopotassium phosphate (KH₂PO₄) covers all phosphorus and adds further potassium. Magnesium sulfate (Epsom salt) covers magnesium and sulfur. Ammonium nitrate tops up the small ammonium-nitrogen fraction. Iron EDTA chelate provides soluble iron. The strength-scale percentage and EC slider simply multiply every target concentration proportionally, which scales all salt weights together.
Worked example
A 100 L DWC reservoir targeting EC 2.0 mS/cm on the General Purpose profile requires:
| Salt | Formula | Mass |
|---|---|---|
| Calcium Nitrate | Ca(NO₃)₂·4H₂O | 94.14 g |
| Potassium Nitrate | KNO₃ | 44.11 g |
| Monopotassium Phosphate | KH₂PO₄ | 13.60 g |
| Magnesium Sulfate | MgSO₄·7H₂O | 48.78 g |
| Ammonium Nitrate | NH₄NO₃ | 4.00 g |
| Iron EDTA | Fe-EDTA | 1.31 g |
Plus micronutrients: Mn 0.154 g, B 0.282 g, Zn 0.113 g, Cu 0.078 g, Mo 0.025 g.
For a 500 L NFT channel at the same EC just multiply all weights by 5 — or simply change the volume input and let the calculator do it instantly.
Formula note
The mass equation follows directly from unit analysis. One litre of solution at 1 mg/L concentration of element E contains 0.001 g of E. To supply that from a compound of molar mass MW that has n atoms of E per formula unit, you need MW/(n × AW_E) grams of compound per gram of element — scaled by the target mass. The factor of 1000 in the denominator reconciles mg with g. This approach is standard in all major hydroponic chemistry references including Resh’s Hydroponic Food Production (8th ed., 2022) and the FAO’s soilless culture guidelines.