EC to PPM Calculator
Convert EC (Electrical Conductivity) to PPM using 500, 640, and 700 scales, then dial in nutrient strength with temperature compensation, source water correction, and crop-specific safety checks.
Quick answer: To convert EC to PPM, multiply your EC reading (mS/cm) by your meter's scale factor — 500, 640, or 700. A 1.4 EC solution reads 700 PPM on a 500-scale meter but 980 PPM on a 700-scale meter. Always confirm your meter's scale before comparing readings with anyone else, or compare EC directly and skip the conversion entirely.
Last verified: July 2026 — conversion factors and meter scales checked against current manufacturer specs.
Nutrient Concentration Calculator
Crop & Growth Stage Intelligence
Quick-pick popular crops (or use the full list above):
Advanced Tools
Temperature Compensation (ATC)
Warmer water conducts electricity more easily, so a raw EC reading taken at 30°C will read higher than the same nutrient strength at the 25°C reference point most crop charts (including this tool) are built around. If your meter doesn't have automatic temperature compensation, correct it here.
Source Water Correction
Tap water usually already carries some baseline EC before you add any nutrients. Enter your untreated source water's EC to see how much of your reservoir reading actually comes from fertilizer, and how much headroom you have before hitting your crop's ceiling.
Safety Checks
Automatically evaluated from your current EC, crop, growth stage, and source water values above.
EC to PPM Converter (Hydroponics Calculator)
EC to PPM Conversion Formula (Quick Answer)
To convert EC (mS/cm) to PPM, multiply by the correct conversion factor:
- 500 scale: EC × 500
- 640 scale: EC × 640
- 700 scale: EC × 700
This EC to PPM calculator automatically applies the correct scale, helping you measure nutrient concentration accurately in hydroponic systems.
What is EC (Electrical Conductivity)?
EC measures how well a solution conducts electricity. In hydroponics, it directly reflects the concentration of dissolved nutrients (ions) in water.
Higher EC = more nutrients available to plants.
What is PPM (Parts Per Million)?
PPM estimates the concentration of nutrients in water, expressed as milligrams per liter (mg/L).
It is derived from EC using a conversion factor (500, 640, or 700 scale). Because of this, PPM is less consistent than EC across different meters.
EC vs PPM (Quick Comparison)
- EC: Direct measurement (more accurate)
- PPM: Converted value (depends on scale)
- Best practice: Use EC for precision and PPM for reference
In professional hydroponic systems, EC is always the primary measurement, while PPM is used for convenience.
Which Scale Does My Meter Use?
Not sure? Mix a 1.0 EC calibration solution and check your meter’s PPM reading — 500 PPM means you’re on the 500 scale, 700 PPM means the 700 scale.
| Meter Brand / Model | Scale | Common Region |
|---|---|---|
| Hanna Instruments (most models) | 500 | North America |
| Milwaukee MW301 / MW302 | 500 | North America |
| Apera Instruments (PC60, EC60) | 500 | North America |
| Most budget TDS pens (unbranded) | 500 | North America |
| Bluelab Truncheon | 700 | Global / Australia |
| Bluelab Combo Pen | 700 (some user-selectable) | Global |
| Eutech / Oakton | 700 | Professional / lab |
| Most European meters | 640 | Europe (KCl-based) |
The 500 scale assumes a NaCl (sodium chloride) standard. The 700 scale assumes a KCl (potassium chloride) standard — that’s why the same solution reads differently depending on which one your meter is built around. EC itself is sometimes written as dS/m instead of mS/cm; it’s the same number, just different notation.
If unsure, rely on EC values for consistency.
EC to PPM Conversion Table — All Three Scales
EC in mS/cm. PPM calculated as EC × scale factor. Stage column is a general reference — check the crop-specific tool above for your actual target.
| EC (mS/cm) | 500 Scale | 640 Scale | 700 Scale | Typical Stage |
|---|---|---|---|---|
| 0.4 | 200 | 256 | 280 | Seedling / RO water |
| 0.6 | 300 | 384 | 420 | Seedling / clone |
| 0.8 | 400 | 512 | 560 | Early veg |
| 1.0 | 500 | 640 | 700 | Veg |
| 1.2 | 600 | 768 | 840 | Veg |
| 1.4 | 700 | 896 | 980 | Veg / transition |
| 1.6 | 800 | 1,024 | 1,120 | Transition / early flower |
| 1.8 | 900 | 1,152 | 1,260 | Early flower |
| 2.0 | 1,000 | 1,280 | 1,400 | Flower |
| 2.2 | 1,100 | 1,408 | 1,540 | Peak flower |
| 2.6 | 1,300 | 1,664 | 1,820 | Max recommended (most crops) |
| 3.0 | 1,500 | 1,920 | 2,100 | Commercial / salt-tolerant only |
Note: EC is the true measurement. PPM values shift depending on which scale your meter uses — the stage column above is a general reference, not a substitute for the crop-specific targets in the calculator above.
About The EC ↔ PPM Hydroponics Calculator
If you’ve spent more than five minutes in hydroponics, you’ve hit the great nutrient confusion wall. Your meter says one thing, the bottle’s chart suggests another, and your plants just sit there looking judgmental. The problem usually isn’t the nutrients—it’s the translation. Electrical conductivity (EC) is the universal, unfiltered measurement of dissolved salts in your solution. PPM is simply a human-friendly conversion of that number, and it depends on scale. That’s exactly why this EC to PPM hydroponics calculator exists: to convert EC accurately using the 500, 640, or 700 scales, so you can feed with confidence instead of guesswork.
How the EC to PPM Hydroponics Calculator Works
The calculator applies the correct conversion factor—500, 640, or 700—to your entered EC value. Because EC is the direct measurement your meter reads, it stays consistent across systems. PPM is the derived number that changes based on the scale used. By anchoring your feeding decisions to EC and using PPM as a reference, your nutrient strategy becomes accurate, repeatable, and free from scale-related confusion. You’re not just getting a number—you’re getting the right number for your system.
Why EC is More Reliable Than PPM
EC measures actual electrical conductivity, which directly represents ion concentration in your nutrient solution.
PPM, on the other hand, is a calculated value that varies depending on the conversion factor used by different manufacturers.
That’s why experienced growers always trust EC first.
Frequently Asked Questions
What’s the difference between EC and PPM? EC (Electrical Conductivity) is what your meter actually measures. PPM is a number calculated from that EC reading using a conversion factor — 500, 640, or 700 — so PPM can vary between meters even when the nutrient strength is identical. EC is the more consistent number to track and share.
Which scale should I use — 500, 640, or 700? Use whatever matches your meter: 500 for most Hanna/Milwaukee TDS meters, 640 for the common European conversion standard, and 700 for Truncheon-style meters common in Australia. If you’re unsure, work directly in EC (mS/cm) instead — it removes the ambiguity entirely.
Why does my EC reading change with water temperature? Higher water temperature increases ion mobility, which makes the solution conduct electricity more easily and pushes the raw EC reading up — even though nutrient strength hasn’t changed. Meters with automatic temperature compensation correct for this in real time; use the Temperature Compensation tool above if yours doesn’t.
Should I subtract my tap water’s EC from my target reading? It’s good practice to know your source water’s baseline EC, especially with hard or well water, since it eats into the nutrient headroom before you’ve added anything. Use the Source Water Correction tool above to see your net nutrient contribution and how much room you have left.
Which meter scale is more accurate — 500 or 700? Neither scale is more accurate; they’re both derived from the same EC reading using different conversion standards — 500 assumes a NaCl basis, 700 assumes KCl. Accuracy comes from your meter’s calibration, not which scale it reports in. Match the scale to your feeding chart, or work in EC directly to sidestep the question entirely.
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