| EC input | Unit | Scale | Factor | TDS output (ppm) | Typical use |
|---|---|---|---|---|---|
| 1.20 | mS/cm | 500 | 500 | 600 | 500-scale meters, many nutrient charts |
| 1.20 | mS/cm | 700 | 700 | 840 | 700-scale meters, KCl-style readings |
| 1200 | uS/cm | 640 | 640 | 768 | 442 solutions, mixed salts estimate |
- TDS (ppm) = EC25 (mS/cm) x Factor
- EC25 = ECmeasured / (1 + a x (T - 25)) (optional)
- ECmeasured = EC25 x (1 + a x (T - 25)) (reverse, optional)
- 1 mS/cm = 1000 uS/cm
Factors like 500, 640, and 700 are common meter scales. They approximate how dissolved salts relate to conductivity in different reference solutions.
- Choose EC -> TDS if you measured EC, or TDS -> EC if you measured ppm.
- Enter the value and select the correct EC unit for your meter.
- Select a conversion factor that matches your device scale or chart.
- Enable temperature compensation if your sample is far from 25C.
- Press Calculate. Review results above the form, then download CSV or PDF.
EC and plant nutrition signal strength
Electrical conductivity indicates the ion load in nutrient water. As EC rises, osmotic pressure increases and roots may absorb water more slowly. Gardeners use EC trends to keep feeds steady across top ups, runoff checks, and reservoir changes. This calculator converts EC to estimated TDS so you can compare records, fertilizer charts, and meter displays using a consistent, repeatable number every time. for better nutrient planning.
Why conversion factors change readings
TDS meters display ppm using an internal factor, commonly 500, 640, or 700. The factor approximates how a reference solution links conductivity to dissolved solids, but fertilizer blends vary. Two meters can show different ppm for the same EC. Selecting the correct factor aligns your readings with your device scale, reduces confusion, and supports consistent reporting across teams. when sharing notes with partners, clients, or staff.
Unit handling for accurate logging
EC can be reported in mS/cm or uS/cm, and the values differ by a thousand. A unit mix up is one of the most common logging errors. The calculator accepts either unit and returns both, helping you match handheld pens, controllers, and lab notes. Reliable unit handling makes trend graphs meaningful when diagnosing dilution, evaporation, sensor drift, or dosing mistakes. during weekly system audits.
Temperature effects and compensation
Conductivity increases with temperature even when the dissolved salts stay unchanged. For comparisons across seasons, optional compensation can normalize readings to 25C, especially when samples are measured at different times of day. The calculator applies a temperature coefficient, often near 2 percent per C for nutrient solutions, to estimate EC at 25C or recover measured EC from ppm. It helps compare winter logs and summer logs.
Using outputs to guide garden decisions
Use the result summary to guide adjustments rather than chasing a single number. If TDS is high, dilute with clean water, mix, then remeasure. If low, add concentrate in small steps and retest. Export CSV or PDF to document batches, crop stages, and weekly maintenance. Pair EC or TDS tracking with pH, drainage, and plant observations, and review thresholds monthly. to keep dosing disciplined and repeatable.
FAQs
Which factor should I choose, 500 or 700?
Use the factor that matches your meter or the chart you follow. Many hobby meters use 500, while some commercial meters use 700. If unsure, check the device manual or compare to a known solution.
Is TDS the same as EC?
No. EC measures conductivity, while TDS is an estimated dissolved solids value derived from EC using a factor. Different factors can produce different ppm numbers for the same EC.
Should I always enable temperature compensation?
Enable it when your sample temperature is far from 25C or when you compare readings taken in different seasons. If your meter already compensates, leave this option off to avoid double correction.
Can I convert ppm back to EC reliably?
You can estimate EC at 25C using the same factor used by the ppm reading. Accuracy depends on the solution makeup and the meter scale, so treat conversions as practical estimates.
What units should I log for hydroponics?
Log both EC in mS/cm and ppm if your team uses both. Consistency matters more than the unit choice. Use the same factor and unit format across your grow log.
Why do my readings drift over time?
Evaporation concentrates salts, top ups dilute them, and plants selectively uptake ions. Sensors can also foul or drift. Calibrate regularly, keep probes clean, and track EC or TDS trends alongside pH and temperature.