EC (Electrical Conductivity) in hydroponics measures the total concentration of dissolved nutrients in your water, expressed in mS/cm. TDS (Total Dissolved Solids) is the same measurement in parts per million (ppm). The conversion factor depends on your meter: ×500 (Hanna/Milwaukee), ×640 (European standard), or ×700 (Truncheon/Australia). This calculator supports all three scales, plus CF units, and checks your reading against 35 crop profiles across four growth stages.
Key Takeaways — What’s New in This Version
- All three PPM scales: 500 (Hanna/Milwaukee), 640 (European), 700 (Truncheon/Australia) — select the one that matches your meter.
- CF unit support: Enter readings in Conductivity Factor (CF = EC × 10) — common in UK and Australia.
- Growth stage targeting: Select Seedling, Vegetative, Fruiting/Flower, or Flush — each stage has different ideal EC targets.
- 35 crop profiles: Including Cannabis/Hemp, Strawberry, Microgreens, Watercress, Rosemary, Thyme, and more.
- Dilution helper: When EC is too high, the tool calculates exactly how much plain water to add to reach your target.
- Bidirectional conversion: Enter EC (any unit) or TDS (ppm) — converts both ways automatically.
- Pro Tip: Always measure your tap water EC first. If it reads 0.3 mS/cm, your nutrients only need to raise EC by (target − 0.3), not from zero.
EC / TDS / CF Calculator for Plants & Crops
Enter your meter reading, select your scale, choose your crop and growth stage, then instantly check if your nutrient solution is in range.
Type to filter the dropdown below.
Vegetative stage selected — using standard crop EC range.
Leave blank if entering TDS/ppm instead.
Leave blank if entering EC instead. Uses selected scale above.
Enter litres to get dilution water amount if EC is too high.
Your EC / TDS / CF Results
💧 Dilution Helper — How much water to add to lower EC
⚠️ Add water in stages and recheck EC — osmosis and temperature affect real results. Remove — litres of current solution first if tank space is limited.
📬 Get a Free EC & pH Management Cheat Sheet
Enter your details and we’ll send our complete EC, TDS & CF reference guide — crop tables, scale comparison, and stage-by-stage targets, ready to print.
📊 EC Range at a Glance — Vegetative Stage, Common Hydroponic Crops
Bar width represents the ideal EC window (mS/cm) during vegetative growth. Scale: 0–4 mS/cm.
What is EC and TDS — and why does the PPM scale matter?
EC (Electrical Conductivity) measures how well your nutrient solution conducts electricity, which directly reflects the total concentration of dissolved mineral salts. TDS (Total Dissolved Solids) expresses the same measurement in parts per million (ppm). The two readings come from the same sensor — the difference is just the conversion factor applied.
This is where growers get confused: the same solution reads differently depending on which scale your meter uses. A solution at 1.6 mS/cm EC reads as 800 ppm on the 500 scale, 1,024 ppm on the 640 scale, and 1,120 ppm on the 700 scale. If you follow a nutrient schedule specifying “800 ppm” but your meter uses the 700 scale, your plants would be severely underfed. Always match your calculator and nutrient schedule to the same scale.
| PPM Scale | Conversion Formula | Common Meters Using This Scale | 1.5 mS/cm EC = ? |
|---|---|---|---|
| 500 Scale | ppm = EC × 500 | Hanna Instruments, Milwaukee, most US brands | 750 ppm |
| 640 Scale | ppm = EC × 640 | European standard (Bluelab, most EU nutrient brands) | 960 ppm |
| 700 Scale | ppm = EC × 700 | Truncheon meter, common in Australia & UK | 1,050 ppm |
| CF | CF = EC × 10 | Used in UK, Australia — older systems | 15 CF |
How to use this EC/TDS/CF calculator
- Select your PPM scale: Choose 500, 640, or 700 at the top to match your meter. If unsure — check your meter’s manual or brand. Hanna/Milwaukee = 500; most EU brands = 640; Truncheon = 700. This changes the ppm output and the ppm-to-EC conversion.
- Choose your EC unit: Toggle between mS/cm, µS/cm or CF. µS/cm values are 1,000× larger than mS/cm (1,500 µS/cm = 1.5 mS/cm). CF values are 10× larger (15 CF = 1.5 mS/cm).
- Search or select your crop: Type in the search box to filter the 35-crop dropdown. Each crop has a researched EC range built in.
- Select your growth stage: Seedling, Vegetative, Fruiting/Flower, or Flush. EC targets differ significantly by stage — seedlings need roughly half the strength of mature plants.
- Enter your EC or ppm reading: Enter whichever value your meter shows. Leave the other field blank — the tool converts both directions. Optionally enter your reservoir volume in litres to enable the dilution helper.
- Click Convert & Check: Results show EC, ppm (on your selected scale), CF, and your crop-stage ideal range. A colour-coded status bar shows whether you’re ideal, too low, or too high.
- Act on the result: Too low → add nutrients in 0.2 mS/cm steps and recheck. Too high → use the dilution helper to see exactly how many litres of plain pH-adjusted water to add.
Ideal EC ranges by crop and growth stage
| Crop | Seedling (mS/cm) | Vegetative (mS/cm) | Fruiting/Flower | Flush |
|---|---|---|---|---|
| Lettuce | 0.6–0.8 | 1.2–1.8 | 1.6–2.0 | 0.5–0.8 |
| Tomato | 0.8–1.2 | 2.0–2.8 | 2.5–3.5 | 0.5–0.8 |
| Pepper / Chili | 0.8–1.2 | 2.0–3.0 | 2.5–3.5 | 0.5–0.8 |
| Cucumber | 0.6–1.0 | 1.7–2.5 | 2.0–3.0 | 0.5–0.8 |
| Basil | 0.4–0.6 | 1.0–1.6 | 1.4–1.8 | 0.4–0.6 |
| Spinach | 0.8–1.0 | 1.8–2.3 | 2.0–2.5 | 0.5–0.8 |
| Strawberry | 0.4–0.6 | 1.0–1.4 | 1.2–1.6 | 0.4–0.6 |
| Broccoli | 1.0–1.4 | 2.8–3.5 | 3.0–3.5 | 0.5–0.8 |
| Cannabis / Hemp | 0.4–0.8 | 1.2–2.0 | 1.6–2.4 | 0.5–0.8 |
| Microgreens | 0.5–0.8 | 0.8–1.2 | N/A | 0.4–0.6 |
EC and TDS problems — causes and fixes
| Problem | Cause | Fix |
|---|---|---|
| EC rising daily | Plants consuming water faster than nutrients — solution concentrating | Top up with plain pH-adjusted water only. Do not add more nutrients until EC returns to target. |
| EC falling daily | Heavy feeding — nutrients consumed faster than water | Top up with standard nutrient solution. Use the Nutrient Calculator to mix the right strength. |
| EC correct but plants yellowing | pH out of range — nutrients locked out despite correct concentration | Check pH immediately. Correct pH before adjusting nutrient concentration. |
| ppm readings don’t match supplier’s schedule | Meter scale mismatch — you’re using a different scale to the nutrient brand | Check which scale your meter and the nutrient brand use. Convert using the scale comparison table above, or always work in EC (mS/cm) to avoid scale issues. |
| EC reading varies with water temperature | EC is temperature-dependent — warmer water reads higher | Quality meters auto-compensate to 25°C. Always check at the same temperature. Keep reservoir below 22°C for root health. |
| Roots browning despite correct EC | Dissolved oxygen too low, not EC itself | Check water temperature (below 22°C). Increase aeration. High EC + warm water dramatically raises root rot risk. |
EC monitoring: hydroponics vs soil
Hydroponic systems
EC is the most important daily measurement in hydroponics. There is no soil buffer — plants experience your nutrient solution directly. Check EC every day during active growth and after any reservoir top-up. Perform full reservoir changes every 7–14 days to reset salt accumulation. Always pair EC checks with pH checks — never adjust one without checking the other.
Soil and raised beds
Soil growers can measure EC in their runoff water to gauge nutrient build-up in the root zone. Runoff EC above 3.0 indicates salt accumulation — flush with clean water. Pair with the Soil NPK Calculator to manage soil fertility and our Compost Calculator to improve soil structure.
Frequently Asked Questions
Related gardening tools
EC management works best when combined with pH monitoring and accurate nutrient dosing. These tools complete the picture.
pH Calculator — always check pH alongside EC. Correct pH range is 5.5–6.5 for hydroponics. Nutrient Calculator — calculate exact gram weights of nutrients to reach your EC target. Water Volume Calculator — know your reservoir volume before mixing nutrients to EC. VPD Calculator — vapour pressure deficit affects how fast plants uptake nutrients at any given EC.
Sources & References
EC and TDS ranges in this tool are based on peer-reviewed horticultural research and extension publications.
- UniversityUniversity of Arizona CEAC — Hydroponic Lettuce Handbook, EC Management Guidelines. ceac.arizona.edu
- ExtensionUniversity of Vermont Extension — Nutrient Solution Management for Hydroponic Vegetable Production. College of Agriculture and Life Sciences.
- RHSRoyal Horticultural Society (RHS) — Electrical conductivity and plant feeding: guidance for greenhouse crops. rhs.org.uk
- ResearchResh, H.M. (2012) — Hydroponic Food Production, 7th Ed. CRC Press. Widely cited EC ranges for hydroponic crop production.
- ExtensionCornell University Cooperative Extension — Water Quality for Greenhouse and Hydroponic Production, Bulletin 122.
- JournalHortScience — Jensen, M.H. & Collins, W.L. (1985). Hydroponic vegetable production. Horticultural Reviews, 7, 483–558.