EC to PPM Converter Calculator

EC to PPM Converter

Convert EC to PPM across all three scales — 500, 640, and 700 — simultaneously. Switch between EC→PPM and PPM→EC, identify your meter's scale, and check whether your reading is on target for your growth stage. EC is the universal standard; this tool bridges the gap when your feeding chart speaks a different language. Questions about your meter? Talk to a Grow Expert.

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EC ↔ PPM Converter

Simple mode converts EC to PPM on all three scales. Switch to PPM to EC to work backwards from a PPM reading.


How to use this converter
  1. EC → PPM: Enter your EC reading — the converter instantly shows the equivalent PPM on all three scales. Select your growth stage to see a target range check.
  2. PPM → EC: Switch the toggle, enter your PPM value, and select your meter's scale. The converter returns the EC and shows the same PPM value expressed on all other scales.
  3. Not sure which scale your meter uses? See the meter brand table below, or mix a 1.0 EC solution and compare your meter's PPM reading — 500 = 500 scale, 700 = 700 scale.
  4. Always anchor decisions to EC — it's the consistent, universal measurement. Use PPM conversions only when cross-referencing feeding charts.

Formulas: PPM₅₀₀ = EC × 500  ·  PPM₆₄₀ = EC × 640  ·  PPM₇₀₀ = EC × 700  ·  EC = PPM ÷ scale

Key insight: A 1.4 EC solution reads 700 PPM (500 scale), 896 PPM (640 scale), or 980 PPM (700 scale). Same nutrient strength — three completely different numbers. This confusion is the #1 reason growers accidentally over- or underfeed.

📊 Three-Scale Comparison Chart Chart ▾

Run the converter above to see your EC expressed across all three PPM scales.

EC to PPM Conversion Table — All Three Scales

EC in mS/cm. PPM values calculated as EC × scale factor. Always verify which scale your meter uses before comparing to feeding charts.
EC (mS/cm) PPM 500 (Hanna/US) PPM 640 (European) PPM 700 (Bluelab) Typical Stage
0.4 200 256 280 Seedling / RO water
0.6 300 384 420 Seedling / Clone
0.8 400 512 560 Seedling transition
1.0 500 640 700 Early 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
2.4 1,200 1,536 1,680 Peak Flower (heavy feeders)
2.6 1,300 1,664 1,820 Max recommended
3.0 1,500 1,920 2,100 Commercial / salt-tolerant only

Which Scale Does My Meter Use?

When in doubt, test your meter with a 1.0 EC calibration solution. 500 PPM = 500 scale · 700 PPM = 700 scale.
Meter Brand / Model PPM Scale Common Region Notes
Hanna Instruments (most models) 500 North America HI98318, HI9813, combo pens
Milwaukee MW301, MW302 500 North America Budget combo meters
Most budget TDS pens ($10–25) 500 North America eBay/Amazon pens, unbranded
General Hydroponics TDS meters 500 North America Sold at most hydro shops
Apera Instruments 500 North America PC60, EC60 series
Bluelab Truncheon 700 Global / ANZ Also displays CF and EC
Bluelab Combo Pen 700 Global User-selectable on some models
Eutech / Oakton 700 Professional Lab-grade instruments
Truncheon (original) 700 UK / Australia Analog float meter
Most European meters 640 Europe Based on KCl standard

Frequently Asked Questions

What is the difference between the 500 scale and 700 scale for PPM?
The 500 scale multiplies EC by 500 (PPM = EC × 500) and is standard on most North American meters including Hanna and Milwaukee brands. The 700 scale multiplies EC by 700 (PPM = EC × 700) and is used by Bluelab, Eutech, and Truncheon. The same nutrient solution at 1.4 EC reads 700 PPM on the 500 scale but 980 PPM on the 700 scale — a 40% difference. Always match your meter's scale to the scale your feeding chart uses, or anchor everything to EC and ignore PPM entirely.

How do I know which PPM scale my meter uses?
Check your meter's manual or look up the model in the brand table above. If still unsure, mix a nutrient solution and read both EC and PPM simultaneously on your meter. If EC = 1.0 and PPM = 500, you're on the 500 scale. If PPM = 700, you're on the 700 scale. Alternatively, EC is always the same regardless of meter — switch your meter to EC mode and use that as your primary measurement.

Is EC or PPM better for hydroponics?
EC is always preferable. It is the actual physical measurement — electrical conductivity — and produces the same reading on every properly calibrated meter, regardless of brand or scale. PPM is a derived number that changes depending on which conversion factor your meter uses. Commercial growers and professional facilities use EC exclusively. PPM is useful only when cross-referencing a feeding chart that doesn't list EC values.

What EC should I run at each growth stage?
General starting points for most hydroponic crops: Seedling/Clone 0.4–0.8 EC · Early Veg 0.8–1.2 EC · Full Veg 1.2–1.8 EC · Transition/Stretch 1.6–2.0 EC · Early Flower 1.8–2.2 EC · Peak Flower 2.0–2.6 EC · Late Flower/Flush 0.4–0.8 EC. These are baselines — adjust up with higher light intensity, CO₂ enrichment, or heavy-feeding genetics, and down with seedlings, clones, or salt-sensitive varieties.

Get a meter you can trust.

Shop Bluelab, Hanna, Apera, and Oakton EC & PPM meters.
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