Hydroponic EC Mixing Calculator
Calculate how to mix nutrient concentrates to reach your target EC for hydroponic systems with precision.
How Hydroponic EC Mixing Is Calculated
EC (Electrical Conductivity) measures the total dissolved salts in your nutrient solution. It is the primary way hydroponic growers ensure plants receive the correct nutrient concentration. EC is measured in milliSiemens per centimeter (mS/cm).
The Mixing Formula
When diluting a concentrated nutrient stock into a reservoir:
Concentrate_Volume = (Target_EC - Water_EC) × Reservoir_Volume / Concentrate_EC
This assumes linear mixing, which is accurate for the dilution ratios used in hydroponics.
Target EC by Growth Stage
| Growth Stage | Target EC (mS/cm) | PPM (500 scale) |
|---|---|---|
| Seedlings | 0.5 - 0.8 | 250 - 400 |
| Early vegetative | 0.8 - 1.2 | 400 - 600 |
| Late vegetative | 1.2 - 1.6 | 600 - 800 |
| Early flowering | 1.6 - 2.0 | 800 - 1000 |
| Peak flowering | 2.0 - 2.6 | 1000 - 1300 |
| Late flowering / ripening | 1.2 - 1.8 | 600 - 900 |
PPM Conversion
Two PPM scales exist, which causes endless confusion:
- 500 scale (US): PPM = EC × 500
- 700 scale (EU/AU): PPM = EC × 700
Always confirm which scale your meter uses before calculating.
Worked Example
Reservoir: 100 liters, tap water EC: 0.3 mS/cm, target EC: 1.8 mS/cm. Nutrient concentrate Part A rated at 200 mS/cm per mL/L:
- EC to add: 1.8 - 0.3 = 1.5 mS/cm
- Using a 2-part system (A+B equal parts):
- Each part contributes half: 0.75 mS/cm each
- Part A: 0.75 / 2.0 (mS per mL/L) = 0.375 mL per liter × 100L = 37.5 mL
- Part B: same = 37.5 mL
Two-Part vs Three-Part Systems
Most hydroponic nutrients are sold as 2-part (A+B) or 3-part (Grow/Micro/Bloom) concentrates. Two-part systems are simpler: mix equal volumes of A and B. Three-part systems allow more precise control over the nitrogen-to-potassium ratio across growth stages but require careful adjustment of each component’s proportion.
Temperature Correction
EC readings change with temperature. Most meters auto-compensate to 25°C. If yours does not, apply: EC_corrected = EC_measured × (1 + 0.02 × (25 - Temp_°C)). A 1°C change alters EC by approximately 2%.