About this tool
Hydroponic Nutrient Calculator is a free, in-browser tool with two jobs: converting between EC and PPM, and working out how much nutrient concentrate to add to a reservoir. Pick a mode at the top; everything is computed on your device with nothing uploaded.
The converter uses PPM = EC (in mS/cm) × scale, and EC = PPM ÷ scale, where the scale is 500 for the US/TDS (500) standard or 700 for the European (700) standard — the same EC reads as a different PPM on each scale, which is why meters must state which they use. The dosing mode uses mL to add = (target EC − current EC) ÷ nutrient strength × volume in liters, where strength is the EC rise per mL added per liter of water (about 0.1 by default). Gallons are converted to liters at 3.78541 L per gallon.
Use the converter to translate a PPM reading from one meter into another's scale, and the dosing mode to bring a reservoir up to a target strength. Add nutrient gradually, stir, and re-measure with your own meter, since concentrates vary between brands.
Frequently asked questions
What is the difference between the 500 and 700 scale?
Both convert the same EC to PPM but with a different factor: the US/TDS scale multiplies EC by 500, the European scale by 700. So EC 1.5 mS/cm reads as 750 ppm on the 500 scale but 1050 ppm on the 700 scale — always check which scale your meter uses.
How is the nutrient dose calculated?
It is (target EC − current EC) ÷ strength × volume in liters. Strength is the EC rise from adding one mL of concentrate per liter of water; the 0.1 default is a starting point, so verify it against your nutrient's label and your own meter.
Why does the tool need the target above the current EC?
Adding concentrate can only raise EC, so the target must be higher than the current reading for a dose to make sense. To lower EC you dilute with plain water instead, which this dosing mode does not calculate.
Are my readings uploaded anywhere?
No. EC and PPM values, reservoir volume and the resulting dose are all computed in your browser and never sent to a server, so the tool works offline.
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