🧪 EC ↔ PPM Converter
Cannabis EC & PPM Targets by Stage
Recommended electrical conductivity ranges for cannabis from seedling to harvest. Values are for nutrient solution (not run-off).
| Stage | EC (mS/cm) | PPM (500 scale) | PPM (700 scale) | pH Target | Zone |
|---|---|---|---|---|---|
| Seedling / Clone | 0.2 – 0.4 | 100 – 200 | 140 – 280 | 5.8 – 6.2 | Minimal |
| Early Veg (wk 1–2) | 0.8 – 1.2 | 400 – 600 | 560 – 840 | 5.8 – 6.2 | Light Feed |
| Late Veg (wk 3–6) | 1.2 – 1.8 | 600 – 900 | 840 – 1260 | 5.8 – 6.2 | Veg Feed |
| Early Flower (wk 1–4) | 1.6 – 2.0 | 800 – 1000 | 1120 – 1400 | 6.0 – 6.5 | Flower Feed |
| Peak Flower (wk 5–9) | 1.8 – 2.4 | 900 – 1200 | 1260 – 1680 | 6.0 – 6.5 | Heavy Feed |
| Late Flower (wk 10+) | 1.4 – 1.8 | 700 – 900 | 980 – 1260 | 6.0 – 6.5 | Taper Feed |
| Flush / Harvest | 0.0 – 0.5 | 0 – 250 | 0 – 350 | 6.0 – 6.5 | Flush |
Vegetable & Herb EC Targets
Hydroponic EC targets for common vegetables and herbs. Lower EC = lighter feeders (leafy greens); higher EC = fruiting crops (tomatoes, peppers).
| Plant | EC Range (mS/cm) | PPM (500 scale) | pH Range | Notes |
|---|---|---|---|---|
| Lettuce | 0.8 – 1.6 | 400 – 800 | 6.0 – 7.0 | Light feeder; high EC causes tip burn |
| Spinach | 1.2 – 2.0 | 600 – 1000 | 6.0 – 7.0 | Moderate feeder; tolerates higher EC |
| Basil | 1.0 – 1.8 | 500 – 900 | 5.5 – 6.5 | Moderate; high EC causes leaf scorch |
| Tomato | 1.0 – 4.5 | 500 – 2250 | 5.8 – 6.3 | Fruit stage 2.5–4.0; seedling 1.0–1.5 |
| Pepper | 1.5 – 3.5 | 750 – 1750 | 5.8 – 6.3 | Fruiting plants need EC above 2.0 |
| Cucumber | 1.0 – 3.5 | 500 – 1750 | 5.5 – 6.5 | Very sensitive to high EC as seedling |
| Strawberry | 1.0 – 2.5 | 500 – 1250 | 5.8 – 6.2 | Moderate feeder; high EC reduces size |
| Kale / Chard | 1.2 – 2.5 | 600 – 1250 | 5.5 – 6.5 | Hardy leafy greens tolerate range well |
| Herbs (mint, cilantro) | 1.0 – 1.8 | 500 – 900 | 5.5 – 6.5 | Light feeders; excess EC makes herbs bitter |
| Microgreens | 0.8 – 1.6 | 400 – 800 | 5.5 – 6.5 | Often no nutrients needed until after cotyledon stage |
Understanding EC, PPM & TDS
Why growers get confused between EC, PPM, and TDS — and which one to use.
EC vs PPM: The Key Difference
EC (Electrical Conductivity) is the universal standard. It directly measures how well your solution conducts electricity — which correlates precisely to dissolved salt concentration. EC is measured in mS/cm (millisiemens per centimeter).
PPM (Parts Per Million) is calculated from EC using a conversion factor. The problem: there is no universal conversion factor. Two main scales exist:
- 500 scale: PPM = EC × 500 (used by Hanna, Bluelab in USA)
- 700 scale: PPM = EC × 700 (used by Truncheon, common in Australia/UK)
Recommendation: Always use EC for precision growing. Only use PPM if you know your meter's exact scale.
Why EC Spikes or Drops
EC rising unexpectedly:
- Plant is drinking water faster than nutrients → solution concentrates
- Water evaporation from reservoir
- Root zone too dry → salt buildup
- Fix: top up with plain pH-adjusted water
EC dropping unexpectedly:
- Plant is absorbing nutrients faster than water
- Dilution from rain or fresh water top-up
- Fix: add nutrients to bring EC back to target
Best practice: Check EC daily and top up alternating between plain water and nutrient solution to keep EC stable.
Run-Off EC: What It Tells You
In soil, coco coir, or rockwool systems, measuring the EC of your run-off (drainage water) gives insight into salt buildup in the root zone.
- Run-off EC = Feed EC ± 0.5: Healthy root zone
- Run-off EC much higher than feed: Salt buildup — flush with 2× the container volume of plain water
- Run-off EC much lower than feed: Roots are depleted — increase feed EC slightly
Hydroponic systems (DWC, NFT, aeroponics) don't have run-off — monitor reservoir EC directly.
EC Meter Calibration & Accuracy
EC meters drift over time and must be calibrated to remain accurate. Most meters come with calibration solution (usually 1.413 mS/cm or 2.76 mS/cm).
Signs your meter needs calibration:
- Readings that don't match expected values for fresh nutrient solution
- Inconsistent readings within the same solution
- It's been more than 2–3 weeks since last calibration
Best EC meters for hydroponics: Bluelab Truncheon, Apera EC60, Hanna HI9813-6 (combo pH/EC/temp), Milwaukee SM802.
Also rinse the probe with distilled water before and after each reading to prevent cross-contamination.
EC & PPM FAQ
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