Hydroponics EC to PPM Calculator
Electrical conductivity (EC) and parts per million (PPM) are both measures of nutrient solution strength in hydroponic systems. They use different units and conversion factors depending on the meter standard used. This calculator converts EC to PPM using the 500, 640, and 700 scales simultaneously so you can cross-reference readings from different meters.
EC to PPM conversion formulas
PPM (500 scale) = EC (mS/cm) x 500
PPM (640 scale) = EC (mS/cm) x 640
PPM (700 scale) = EC (mS/cm) x 700
Note: EC is measured in mS/cm. Some meters display in microsiemens (uS/cm); divide by 1,000 to convert to mS/cm. The 500 scale is the NaCl standard used in most North American meters (Hanna, Milwaukee). The 700 scale is the KCl standard used in Truncheon meters. Always note which scale your meter uses.
Target EC ranges by crop (University of Arizona CEAC)
- Seedlings and propagation: EC 0.60 to 1.00 mS/cm.
- Lettuce and leafy greens: EC 0.80 to 1.60 mS/cm.
- Herbs (basil, parsley): EC 1.00 to 1.60 mS/cm.
- Tomatoes (vegetative): EC 1.50 to 2.50 mS/cm.
- Tomatoes (fruiting): EC 2.00 to 3.50 mS/cm.
- Cucumbers: EC 1.50 to 2.50 mS/cm.
- Strawberries: EC 1.00 to 1.80 mS/cm.
Hydroponics EC calculator: frequently asked questions
What is EC in hydroponics?
EC (electrical conductivity) measures the total dissolved salts (nutrients) in a hydroponic solution, expressed in milliSiemens per centimeter (mS/cm) or milliSiemens per meter (mS/m). Higher EC indicates more dissolved nutrients. A properly calibrated EC meter is the primary tool for monitoring nutrient solution strength in hydroponic systems.
What is the difference between the 500, 640, and 700 PPM conversion scales?
PPM meters estimate total dissolved solids (TDS) by multiplying EC by a conversion factor. The 500 scale (NaCl standard, used by Hanna and Milwaukee meters) multiplies EC (in microsiemens) by 0.5. The 640 scale (KCl standard) multiplies by 0.64. The 700 scale (used by Truncheon meters in Europe and Australia) multiplies by 0.7. The 500 scale is most common in North America.
What EC should I target for lettuce and leafy greens?
Lettuce and leafy greens grow well at EC 0.8 to 1.6 mS/cm. Higher EC causes tip burn in sensitive varieties. Seedlings should start at EC 0.6 to 0.8 mS/cm. These ranges are consistent with recommendations from the University of Arizona Controlled Environment Agriculture Center.
What EC should I target for tomatoes and fruiting crops?
Tomatoes and peppers in hydroponic production typically target EC 2.0 to 3.5 mS/cm during fruiting. Propagation and early seedling stages use EC 1.5 to 2.0 mS/cm. Higher EC can increase fruit solids (Brix) but reduces yield volume. University of Florida IFAS and UC Davis extension publish crop-specific EC targets.
How often should I check EC in a recirculating hydroponic system?
EC should be checked daily in active growing systems. As plants take up water faster than nutrients (which is common in warm conditions), EC rises; if plants take up nutrients faster than water, EC drops. Adjust by adding fresh nutrient solution or diluting with water. Flush and replace the entire solution every 1 to 2 weeks in most commercial systems.
Official sources
- University of Arizona Controlled Environment Agriculture Center: Hydroponic Nutrient Management.
- University of Florida IFAS Extension: Hydroponic Nutrient Solutions (CV296).
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.