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EC to PPM Hydroponics Calculator

Convert EC (mS/cm) to PPM instantly for any hydroponic system. Supports Hanna (×500), Eutech (×640), and Bluelab (×700) scales. Includes crop reference table.

Data verified · June 2026
Edited by Martín Rodríguez
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Edited by: Martín Rodríguez (editorial policy ) · Last editorial review: Jun 20, 2026

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EC (Electrical Conductivity) measures the total dissolved salts in your nutrient solution in milli-Siemens per centimeter (mS/cm). PPM (Parts Per Million) translates that conductivity into an approximate concentration of dissolved solids. Because EC meters and PPM pens are both widely used in hydroponics, growers must convert between the two using a scale factor: PPM = EC (mS/cm) × Scale.

Three industry scales exist: 500 (Hanna, HM Digital — most common in North America), 640 (Eutech, Milwaukee), and 700 (Bluelab, European brands). A nutrient solution reading EC 1.5 mS/cm equals 750 ppm on the 500 scale, 960 ppm on the 640 scale, or 1,050 ppm on the 700 scale — a 40% spread that can cause serious over- or under-feeding if you use the wrong scale.

When to use this calculator

Dialing in vegetative-stage nutrient strength for lettuce or basil (target EC 1.2–2.0 mS/cm / 600–1,000 ppm on scale 500) without overfeeding young root systems.
Cross-checking a Bluelab Combo meter (scale 700) against a Hanna HI-9813 (scale 500) to confirm both meters agree on the same reservoir batch.
Converting a nutrient manufacturer's feed chart (written in EC) to the PPM scale on your home TDS pen so you can follow the schedule exactly.
Troubleshooting salt build-up in a DWC system when runoff PPM is 30%+ higher than input, signaling excessive fertilizer accumulation.

EC to PPM Conversion — Three Industry Scales

EC (mS/cm)	PPM ×500 (Hanna/HM Digital)	PPM ×640 (Eutech/Milwaukee)	PPM ×700 (Bluelab/European)
0.5	250	320	350
1.0	500	640	700
1.5	750	960	1,050
2.0	1,000	1,280	1,400
2.5	1,250	1,600	1,750
3.0	1,500	1,920	2,100
3.5	1,750	2,240	2,450
4.0	2,000	2,560	2,800
5.0	2,500	3,200	3,500

Fuente: Bluelab – Understanding EC and PPM; University of Arizona CEAC Hydroponic Crop Nutrient Guidelines. Fórmula: PPM = EC (mS/cm) × factor de escala. La diferencia entre escala 500 y 700 puede llegar al 40% para el mismo valor de EC.

How it works

How It's Calculated

EC meters pass a small electrical current through the solution and measure resistance. The conductivity value (mS/cm) is then multiplied by a fixed scale factor to produce PPM:

PPM (Scale 500) = EC (mS/cm) × 500
PPM (Scale 640) = EC (mS/cm) × 640
PPM (Scale 700) = EC (mS/cm) × 700

Most US and Canadian nutrient brands (General Hydroponics, Advanced Nutrients, Fox Farm) publish schedules in EC (mS/cm). TDS pens sold in North America predominantly use Scale 500. European and Australian brands (Canna, Plagron) and the Bluelab Truncheon use Scale 700. Eutech and some Milwaukee instruments use Scale 640.

> ⚠️ Temperature affects conductivity: EC increases ~2% per °C rise. Quality meters auto-compensate to 25 °C (77 °F). Always calibrate with a fresh 1,413 µS/cm standard solution.

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EC to PPM Conversion Table (All Three Scales)

EC (mS/cm)	PPM ×500 (Hanna)	PPM ×640 (Eutech)	PPM ×700 (Bluelab)
0.5	250	320	350
1.0	500	640	700
1.5	750	960	1,050
2.0	1,000	1,280	1,400
2.5	1,250	1,600	1,750
3.0	1,500	1,920	2,100
3.5	1,750	2,240	2,450
4.0	2,000	2,560	2,800
5.0	2,500	3,200	3,500

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Crop Reference Table — Target EC and PPM by Growth Stage

Crop / Stage	Target EC (mS/cm)	PPM ×500	PPM ×700
Seedlings / Clones	0.4 – 0.8	200 – 400	280 – 560
Lettuce / Spinach	1.2 – 1.8	600 – 900	840 – 1,260
Herbs (basil, mint)	1.0 – 1.6	500 – 800	700 – 1,120
Tomatoes (vegetative)	2.0 – 3.5	1,000 – 1,750	1,400 – 2,450
Tomatoes (fruiting)	3.5 – 5.0	1,750 – 2,500	2,450 – 3,500
Cucumbers	1.7 – 2.5	850 – 1,250	1,190 – 1,750
Strawberries	1.0 – 1.4	500 – 700	700 – 980
Cannabis (vegetative)	1.0 – 2.0	500 – 1,000	700 – 1,400
Cannabis (flowering)	1.5 – 2.5	750 – 1,250	1,050 – 1,750

Source: University of Arizona CEAC crop guidelines; General Hydroponics feed charts.

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Worked Examples

Example 1 — Lettuce, Hanna meter (Scale 500)
EC 1.6 mS/cm → PPM = 1.6 × 500 = 800 ppm ✓ (optimal: 600–900 ppm)

Example 2 — Tomatoes fruiting, Bluelab (Scale 700)
Target EC 4.0 mS/cm → PPM = 4.0 × 700 = 2,800 ppm.
Mistakenly using scale 500: 4.0 × 500 = 2,000 ppm — a 28% under-read, which could lead you to add nutrients and push EC to 5.6 mS/cm, causing salt stress.

Example 3 — Cross-meter verification
Bluelab Truncheon shows 1,050 ppm (scale 700) → EC = 1,050 ÷ 700 = 1.5 mS/cm → Hanna reading should be 1.5 × 500 = 750 ppm. If both match, meters are calibrated correctly.

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Common Mistakes

1. Assuming all TDS meters use the same scale. 1,000 ppm on a scale 500 meter = EC 2.0 mS/cm; on a scale 700 meter it = EC 1.43 mS/cm.
2. Ignoring source water EC. Tap water can carry EC 0.2–0.8 mS/cm. Measure it first and add nutrients to reach total target EC.
3. Not temperature-compensating. A solution at 30 °C reads ~10% higher EC than at 25 °C. Formula: EC_corrected = EC_measured ÷ (1 + 0.02 × (T°C − 25)).
4. Confusing EC units. 1 mS/cm = 1,000 µS/cm = 1 dS/m. A pen showing "1500 µS/cm" is EC 1.5 mS/cm.
5. Using expired calibration solution. Sachets degrade after opening; an uncalibrated probe can drift ±0.3 mS/cm = ±150–210 ppm error.

Worked Example — Lettuce in DWC with a Hanna Meter

Your Hanna HI-9813 reads EC 1.6 mS/cm in your lettuce reservoir.

Hanna meters use Scale 500.

PPM = 1.6 × 500 = 800 ppm.

Optimal range for mature lettuce is 600–900 ppm (scale 500). No adjustment needed.

If you had a Bluelab Truncheon (scale 700): 1.6 × 700 = 1,120 ppm — same solution, different display.

800 ppm (scale 500) = 1,120 ppm (scale 700)

Frequently asked questions

What is the difference between Scale 500, 640, and 700 in hydroponics?

These are the multipliers used to convert EC (mS/cm) to PPM. Scale 500 is standard on most North American TDS pens (Hanna, HM Digital). Scale 640 is used by Eutech and Milwaukee instruments. Scale 700 is used by Bluelab and European brands. For EC 2.0 mS/cm: Scale 500 → 1,000 ppm; Scale 640 → 1,280 ppm; Scale 700 → 1,400 ppm. Always check your meter's manual.

How do I find out which scale my TDS pen uses?

Check the product manual or manufacturer's website. As a field test: measure a 1.413 mS/cm calibration fluid and observe the ppm reading — 706 ppm = scale 500; 904 ppm = scale 640; 989 ppm = scale 700. Most pens sold under $30 on Amazon use scale 500 by default.

Should I measure EC or PPM for hydroponics?

EC (mS/cm) is the scientifically preferred unit because it is a direct physical measurement. PPM is derived from EC via a scale factor, meaning it can misrepresent ionic concentration if the wrong scale is used. Most agronomic research and commercial greenhouse guides publish nutrient targets in EC. Use PPM only when your meter doesn't display EC.

What EC should I target for cannabis in the flowering stage?

Most experienced growers recommend EC 1.5–2.5 mS/cm (750–1,250 ppm on scale 500) during flowering. Late flowering (final 2 weeks before flush) is typically tapered to EC 1.0–1.5 mS/cm. Exceeding EC 3.0 mS/cm during flowering can cause salt stress, tip burn, and nutrient lockout.

Does temperature affect EC and PPM readings?

Yes. EC increases approximately 2% per °C above 25 °C (77 °F). A solution at 30 °C reads ~10% higher than the same solution at 25 °C. To manually correct: EC_corrected = EC_raw ÷ (1 + 0.02 × (T − 25)). Meters with Automatic Temperature Compensation (ATC) perform this internally.

How does source water EC affect my nutrient solution?

Source water (tap, well, municipal) always carries dissolved minerals — typically EC 0.1–0.8 mS/cm. This baseline contributes to your total PPM and can include calcium, sodium, and bicarbonates that interfere with nutrient ratios. Always measure source water EC first, then add nutrients until you reach the total target EC.

What happens if EC is too high or too low for my plants?

EC too high (above crop maximum): causes osmotic stress — roots cannot absorb water effectively, leading to wilting, tip burn, and stunted growth. EC too low (below crop minimum): causes nutrient deficiency symptoms — yellowing (nitrogen), purple tints (phosphorus), interveinal chlorosis (magnesium). Flush the system with pH-balanced water if EC exceeds the upper limit by more than 0.5 mS/cm.

Can I convert PPM back to EC?

Yes. Divide your PPM reading by the scale factor of your meter: EC (mS/cm) = PPM ÷ scale. Example: 1,000 ppm on a scale 500 meter → EC = 1,000 ÷ 500 = 2.0 mS/cm. On a scale 700 meter: 1,000 ppm → EC = 1,000 ÷ 700 = 1.43 mS/cm. This reverse conversion is useful when a nutrient chart lists targets in EC but your meter only shows PPM.

Is EC 1.0 mS/cm the same as 1,000 µS/cm?

Yes, exactly. The unit prefixes differ but the values are equivalent: 1 mS/cm = 1,000 µS/cm = 1 dS/m. If your meter displays 1,500 µS/cm, that is EC 1.5 mS/cm. This is a common source of confusion when switching between meter brands or reading older research papers.

Sources & references

Methodology & trust

Editorial

Calculadora de jardineria revisada por el equipo editorial de Hacé Cuentas, contrastada con University of Arizona CEAC – Hydroponic Crop Nutrient Guidelines, según nuestra política editorial y metodología.

Updates

Última revisión: June 20, 2026. Los parámetros se verifican periódicamente con las fuentes citadas.

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Limitations

Indicative results. For critical decisions, consult a professional.

📌 How to cite this calculator

Rodríguez, M. (2026). EC to PPM Hydroponics Calculator. Hacé Cuentas. https://hacecuentas.com/hydroponic-nutrients-ec-ppm

Contenido bajo licencia CC-BY 4.0 — reutilizable citando la fuente con enlace a Hacé Cuentas.

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