Hydroponic Nutrient Calculator
The hydroponic nutrient calculator converts between electrical conductivity (EC) and parts per million (ppm) and calculates how much stock nutrient solution to add to your reservoir to hit your target EC. Correct EC management is the single most important factor in hydroponic crop productivity: too low and plants are nutrient-deficient; too high and osmotic stress prevents water uptake. Enter your reservoir volume, current EC, and target EC to find out exactly how much stock solution to add.
EC and ppm conversion formula
ppm (500 scale) = EC (mS/cm) x 500
ppm (700 scale) = EC (mS/cm) x 700
EC deficit = Target EC - Current EC
Stock to add (mL) = EC deficit x Reservoir (L) / (EC per mL of stock)
Frequently asked questions
What is EC in hydroponics?
EC (electrical conductivity) measures the total dissolved salts (nutrient ions) in a solution, expressed in millisiemens per centimetre (mS/cm) or microsiemens per centimetre (uS/cm). Higher EC means more nutrients. Most hydroponic crops grow best at 1.2 to 2.4 mS/cm. Seedlings prefer lower EC (0.8 to 1.2); mature fruiting plants prefer higher EC (2.0 to 3.0).
How do I convert EC to ppm?
The conversion depends on the reference standard used. In North America, ppm(500) = EC x 500. In Europe and Australia, ppm(700) = EC x 700. A solution at 2.0 mS/cm contains approximately 1,000 ppm using the 500 scale or 1,400 ppm using the 700 scale. Check which standard your nutrient meter uses.
What target EC should I use for different crops?
Lettuce and leafy greens: 1.2 to 2.0 mS/cm. Basil and herbs: 1.0 to 1.6 mS/cm. Tomatoes: 2.0 to 4.0 mS/cm (higher during fruit set). Cucumbers: 1.7 to 2.5 mS/cm. Strawberries: 1.4 to 2.0 mS/cm. These ranges are derived from USDA Cooperative Extension hydroponic research publications.
What is the Hoagland nutrient solution?
The Hoagland solution, developed by Hoagland and Arnon at the University of California, is the standard reference nutrient solution for hydroponic research. The full-strength Hoagland solution has an EC of approximately 2.0 mS/cm and provides all essential macro and micronutrients. Half-strength is often used for seedlings and sensitive crops.
How do I adjust EC if it is too high or too low?
If EC is too high, dilute the solution by adding plain reverse osmosis or distilled water. If EC is too low, add more nutrient concentrate or mixed nutrient solution. Adjust in small increments and re-test. Always also check pH (target 5.5 to 6.5 for most crops) as pH affects nutrient availability even when EC is correct.
Sources
- USDA NIFA: USDA NIFA - Specialty Crop Research Initiative (hydroponics).
- Hoagland and Arnon (1950): The Water-Culture Method for Growing Plants Without Soil. University of California Circular 347. (Reference via USDA NAL.)
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.