Hydroponic Nutrient Calculator
Mixing the right nutrient strength is the difference between thriving hydroponic plants and burned, stunted ones. This free hydroponic nutrient ppm calculator tells you exactly how much nutrient concentrate to add to your reservoir — in teaspoons, tablespoons, milliliters, or fluid ounces — based on your current and target ppm, plus your nutrient brand's label rate.
Enter your numbers
The dose printed on your nutrient bottle, e.g. "2 tsp per gallon".
The ppm that the label dose is supposed to produce. If the label doesn't say, use your target ppm.
Your results
| Tablespoons | — |
| Milliliters | — |
| Fluid ounces | — |
| Target EC (500 scale) | — |
| Target EC (700 scale) | — |
| Water to add to | — |
How to use this calculator
First, measure your reservoir with a TDS/EC meter and enter the reading as "Current ppm". If you're starting with fresh water, enter 0. Next, pick your target ppm — your nutrient brand's feed chart will list one for your plants' growth stage (for example, leafy greens often run 400–800 ppm, while fruiting crops run 800–1,500 ppm).
Then enter the dose printed on your nutrient label ("2 tsp per gallon") and the ppm that dose is meant to produce. If the label doesn't give a reference ppm, enter the same value as your target ppm — this assumes the label dose brings fresh water exactly to that strength. Hit calculate and you'll get the exact amount of nutrient to add, in whichever unit is most convenient for your syringe or measuring spoons.
Always add nutrients to water, never pour water into the concentrate. Stir thoroughly, let the solution sit a few minutes, then re-measure with your meter before feeding your plants.
How it works
The calculator scales your nutrient dose proportionally to the gap between your current and target ppm, relative to what the label dose is expected to achieve:
Dose ratio = (target ppm − current ppm) ÷ label reference ppm
Total nutrient = dose ratio × label tsp per gallon × gallons of water
Conversions are exact: 1 tablespoon = 3 teaspoons, 1 teaspoon = 4.92892 ml, and 1 fluid ounce = 29.5735 ml. EC is shown on both common scales: EC (mS/cm) = ppm ÷ 500 for the US/NaCl scale, and ppm ÷ 700 for the European/Australian KCl scale. For example, 800 ppm equals 1.6 mS/cm on the 500 scale and about 1.14 mS/cm on the 700 scale.
Assumptions and caveats. This math assumes nutrient strength rises in a straight line with the dose, which holds well for most one-part nutrients but can drift with complex multi-part recipes — always confirm with a meter. pH adjustment is a separate step and is not covered here. Label rates vary widely between brands, so check your specific product's feed chart; the numbers here are estimates to guide mixing, not a guarantee of plant outcomes.
Frequently asked questions
What is the difference between ppm and EC?
Both measure nutrient strength. EC (electrical conductivity) is the actual physical measurement of dissolved salts in your solution, in mS/cm. ppm (parts per million) is a conversion of EC that meters estimate using a scale. Because different meters use different conversion scales (500 or 700), EC is the more universal number to share with other growers.
What is the 500 vs 700 ppm scale?
Meters convert EC to ppm by multiplying by a fixed factor: the 500 scale (NaCl, common in the US) uses ppm = EC × 500, and the 700 scale (KCl, common in Europe and Australia) uses ppm = EC × 700. This calculator uses the 500 scale by default and also shows the 700-scale equivalent. Check your meter's manual to see which scale it uses.
My reservoir already has nutrients in it. How do I use this calculator?
Enter your measured value in the "current ppm" field. The calculator only doses the difference between your current reading and your target ppm, so it will not double-dose your reservoir.
How do I use this calculator with two-part (A/B) nutrients?
Calculate the total amount as usual, then split it evenly between part A and part B unless the label says otherwise. Mix each part into the water separately — never mix the concentrates together directly — and stir well between additions.
Can I overdose my hydroponic plants with nutrients?
Yes. Too-strong solution (nutrient burn) shows as brown, crispy leaf tips and can stunt growth. If you are unsure, start at half the calculated dose, check the ppm with a meter, and work up gradually. Always follow your nutrient brand's feed chart for the growth stage of your plants.