EC/TDS Calculator for Hydroponics & Plants | Free Online Tool

Key Takeaways

What it does: Converts EC (mS/cm) ↔ TDS (ppm) instantly and checks whether your reading is in the ideal range for your selected crop.
20+ crop profiles: Each crop has a researched ideal EC range — select yours and the tool tells you if you’re too low, ideal, or too high.
Two conversion directions: Enter EC to get TDS, or enter TDS to get EC — whichever reading your meter shows.
Conversion factor used: This calculator uses the 640 factor (1 EC = 640 ppm) — the most widely used standard for hydroponic nutrient solutions.
Pro Tip: Always measure EC before adding nutrients and again after mixing. If your tap water reads above 0.4 EC, subtract that from your target — you’re already partway there.

EC TDS calculator for hydroponics — convert EC to ppm and check crop nutrient levels

EC/TDS Calculator for Plants & Crops

Enter your EC or TDS reading, select your crop, and instantly check if your nutrient solution is in range.

Search Crop (type to filter)

Dropdown filters as you type.

Select Crop

Enter EC (mS/cm)

Leave blank if entering TDS instead.

— OR —

Enter TDS (ppm)

Leave blank if entering EC instead.

Your EC/TDS Results

EC Reading

—

mS/cm

TDS Equivalent

—

ppm (×640)

Ideal Range

—

mS/cm for crop

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What is EC and TDS and why do they matter?

EC (Electrical Conductivity) measures how well a solution conducts electricity — and since dissolved mineral salts conduct electricity, EC directly tells you the total concentration of nutrients in your water. The higher the EC, the more nutrients are dissolved. TDS (Total Dissolved Solids) is the same measurement expressed as parts per million (ppm) rather than milliSiemens per centimetre (mS/cm). Both readings come from the same meter — different brands just display in different units.

In a hydroponic system, EC is the most important number you monitor daily. Too low and plants show slow growth, yellowing leaves, and weak stems because they’re not receiving enough minerals. Too high and the solution draws water OUT of the roots through osmosis — causing tip burn, wilting, and root damage even when the reservoir is full. Every crop has its own preferred EC window, which is why this calculator checks your reading against crop-specific ranges rather than a generic value. Use it alongside our pH Calculator — EC and pH must both be correct simultaneously for nutrients to be absorbed.

How to use this EC/TDS calculator

Search or select your crop: Type in the search box to filter the crop dropdown. Each crop has a researched ideal EC range built in — selecting your crop enables the range check after conversion.
Enter your EC or TDS reading: Enter whichever value your meter shows — EC in mS/cm OR TDS in ppm. Leave the other field blank. The tool converts in both directions automatically.
Click Convert & Check: The calculator shows both EC and TDS values and compares your reading to the ideal range for your selected crop.
Read your status: Green means you’re in range. Blue means too low — add nutrients gradually. Orange means too high — dilute with plain pH-adjusted water.
Act on the result: If EC is too low, add nutrients in small increments and recheck. Never add large amounts at once — aim for 0.2 mS/cm increases at a time. Use our Nutrient Calculator to calculate exact gram weights needed.
Monitor daily: EC rises as water evaporates (plants drink water faster than nutrients), and falls when plants are feeding heavily. Top up with plain water when EC rises, and with nutrient solution when EC falls. Perform a full reservoir change every 7–14 days.

Pro Tip: Always measure your tap water EC before mixing nutrients. Most tap water reads 0.2–0.5 mS/cm from naturally dissolved minerals. Your nutrient dose should raise EC from this base to your target — not from zero. For example: if tap water EC is 0.3 and your target is 1.5, you only need to add nutrients to raise by 1.2 mS/cm, not 1.5.

Ideal EC and TDS ranges by crop

Crop	Ideal EC (mS/cm)	TDS Equivalent (ppm)	Key Notes
Lettuce	1.2 – 1.8	768 – 1,152	Light feeder. Exceeding 2.0 EC causes tip burn on outer leaves.
Basil	1.0 – 1.6	640 – 1,024	Very sensitive to overfeeding. Keep pH at 5.8–6.2.
Spinach	1.8 – 2.3	1,152 – 1,472	Cool-season crop — EC needs are moderate. Watch for bolting.
Tomatoes	2.0 – 3.5	1,280 – 2,240	Heavy feeder. EC rises during fruiting stage — 2.5–3.5 for mature plants.
Peppers	2.0 – 3.5	1,280 – 2,240	Similar to tomatoes. High K needed during fruiting — track with Growth Tracker.
Cucumbers	1.7 – 2.5	1,088 – 1,600	Heavy water consumers. EC rises fast — check daily during fruiting.
Strawberries	1.0 – 1.4	640 – 896	One of the most EC-sensitive crops. Keep below 1.6 at all times.
Herbs (general)	1.0 – 1.6	640 – 1,024	Mint, cilantro, chives. Light feeders — err on the low side.
Broccoli	2.8 – 3.5	1,792 – 2,240	Highest EC of common crops. Needs very balanced NPK at this strength.
Microgreens	0.8 – 1.2	512 – 768	Harvested before mature feeding stage — keep EC very low throughout.

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 drops back to target.
EC falling daily	Plants feeding heavily — nutrients being consumed faster than water	Top up with your standard nutrient solution. Use 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. Target 5.5–6.5. Correct pH before adjusting nutrient concentration.
Tip burn on lettuce despite ideal EC	Calcium deficiency caused by low transpiration at high humidity	Improve airflow around the canopy. EC is less important than Calcium delivery speed — increase VPD slightly.
EC reading inconsistent between tests	Temperature affects EC readings — warmer water shows higher EC	Calibrate your meter. Most meters auto-compensate to 25°C — check your meter’s spec. Always measure at the same temperature.
Roots browning despite correct EC	EC may be correct but dissolved oxygen is low — root rot developing	Check water temperature (keep below 22°C). Increase aeration. High EC + warm water = root rot risk.
EC won’t rise despite adding nutrients	Meter needs calibration, or solution is at capacity (precipitation forming)	Calibrate meter with EC calibration solution. If nutrients are precipitating, do a full reservoir change.

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. Target a stable EC by replacing water lost to evaporation with plain water and nutrients lost to plant uptake with nutrient solution. Full reservoir changes every 7–14 days 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 how nutrients are building up in the root zone. High runoff EC (above 3.0) indicates salt accumulation — flush with clean water. In raised beds, EC management is less critical than in hydroponics because soil organic matter buffers extremes. Pair with the Soil NPK Calculator to manage soil fertility — and use our Compost Calculator to improve soil structure which naturally buffers EC swings.

Frequently Asked Questions

What is the difference between EC and TDS?

EC and TDS measure the same thing — the concentration of dissolved minerals in water — but use different units. EC is measured in milliSiemens per centimetre (mS/cm) and TDS in parts per million (ppm). The conversion depends on which factor your meter uses: the 500 factor gives TDS = EC × 500, while the 640 factor (used here) gives TDS = EC × 640. Most hydroponic nutrient manufacturers and professional growers use the 640 factor. If your meter uses 500, multiply the TDS result here by 500/640 (≈0.78) to match your reading.

What EC should I start with for seedlings?

Start seedlings at 0.4–0.8 mS/cm — roughly half the lowest recommended EC for your crop. Seedling roots are delicate and burn easily at full strength. Gradually increase EC by 0.2 mS/cm every few days as plants establish. The Germination Timer can help you track when seedlings are ready to move to a stronger solution — typically when the first true leaves appear, about 3–5 days after sprouting.

Why does my EC keep rising even though I’m not adding nutrients?

This is the most common EC management question. When plants drink water faster than they consume nutrients, the nutrient concentration in the remaining water increases — causing EC to rise. This happens most often in warm conditions or during rapid vegetative growth. The fix is simple: top up the reservoir with plain, pH-adjusted water (no nutrients) until EC returns to your target. Never add more nutrient solution when EC is already at or above target.

Can I use the same EC target for all growth stages?

No — plants need different EC levels at each stage. Seedlings need 0.4–0.8. Vegetative plants need the standard crop range (shown in the table above). Fruiting plants — tomatoes, peppers, cucumbers — typically need 0.5–1.0 mS/cm higher EC during the fruiting stage than during vegetative growth, because fruit production is energy-intensive and demands more minerals. Use the Nutrient Calculator to adjust your recipe for each stage rather than using one fixed formula throughout.

My EC meter is showing a different reading than last week — is it broken?

Probably not broken — EC meters drift and need regular calibration. Calibrate with a fresh EC calibration solution (usually 1.413 or 2.764 mS/cm standards) every 1–2 weeks. Also check water temperature: EC readings are temperature-dependent, and a 10°C difference in water temperature changes EC readings by roughly 2% per degree. Good quality meters compensate for temperature automatically — check your meter’s manual to confirm this feature is enabled.

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. Growth Rate Tracker — monitor plant development alongside your EC readings.

Learn more from our EC/TDS Guide