Grow Pops
Open menu

Know your number. Know your scale.

EC to PPM calculator & conversion chart

Convert EC to PPM or PPM to EC on the 500, 640 and 700 scales. Made for hydroponic growers, including DWC and RDWC.

Free grow tool

Convert your reading

Which reading do you have?

Enter your reading and choose the unit shown on your meter. 1 mS/cm = 1,000 µS/cm.

Prefer a chart? Jump to the table ↓

Same reading. Different scales.

1.5mS/cm EC

1,500 µS/cm EC

PPM 500
750
PPM 640
960
PPM 700
1,050

Results are rounded for readability. Use the PPM scale that matches your meter or feeding chart.

Conversion example: 1.5 EC to PPM

This fixed example explains the conversion. Your live results appear in the calculator above.

1.5 mS/cm EC equals 750 PPM on the 500 scale, 960 PPM on the 640 scale, or 1,050 PPM on the 700 scale. It is also 1,500 µS/cm. The conductivity is the same; the conversion factor changes.

This tool converts readings. The numbers are not recommended feeding strengths or measurements of individual nutrients.

Keep it handy

EC to PPM conversion chart

Back to calculator ↑

Find EC from 0.1 to 3.0 mS/cm in 0.1 steps. The calculator above also accepts values between and beyond these rows.

On a small screen, scroll the table sideways to see every scale.

EC in mS/cm and µS/cm, with equivalent PPM readings on 500, 640 and 700 scales.
EC mS/cmEC µS/cmPPM 500 scalePPM 640 scalePPM 700 scale
0.1100506470
0.2200100128140
0.3300150192210
0.4400200256280
0.5500250320350
0.6600300384420
0.7700350448490
0.8800400512560
0.9900450576630
1.01,000500640700
1.11,100550704770
1.21,200600768840
1.31,300650832910
1.41,400700896980
1.51,5007509601,050
1.61,6008001,0241,120
1.71,7008501,0881,190
1.81,8009001,1521,260
1.91,9009501,2161,330
2.02,0001,0001,2801,400
2.12,1001,0501,3441,470
2.22,2001,1001,4081,540
2.32,3001,1501,4721,610
2.42,4001,2001,5361,680
2.52,5001,2501,6001,750
2.62,6001,3001,6641,820
2.72,7001,3501,7281,890
2.82,8001,4001,7921,960
2.92,9001,4501,8562,030
3.03,0001,5001,9202,100

The highlighted row is the 1.5 EC example. This is a conversion chart, not a feeding schedule.

How to convert EC and PPM

When EC is in mS/cm:

  • PPM = EC × 500, 640 or 700
  • EC = PPM ÷ 500, 640 or 700

When EC is in µS/cm, multiply by 0.5, 0.64 or 0.7 to get the corresponding PPM. Divide by that factor to go back to µS/cm.

For example, 1,000 PPM = 2.0 mS/cm on the 500 scale, but approximately 1.43 mS/cm on the 700 scale. That is why PPM always needs a scale.

For normal readings, EC in mS/cm displays up to two decimal places; µS/cm and PPM display as whole numbers. Very small readings retain extra detail so they do not round to zero. Calculations keep full precision; only displayed and copied results are rounded. Rounding does not change your meter’s accuracy.

Why do PPM meters disagree?

A conductivity-based PPM meter measures electrical conductivity, then applies a conversion factor to estimate total dissolved solids. Two meters using different factors can display different PPM numbers for the same EC.

500 vs 700: at 1.0 mS/cm, one shows 500 PPM and the other shows 700 PPM. The water has not changed. The math has.

The 640 scale means a factor of 0.64 applied to EC in µS/cm. Use it only if your meter or reference specifies that factor. Other factors exist, including 0.65; 640 and 650 are not interchangeable.

Check your meter’s settings or manual. If the scale is unknown, compare readings in EC with matching units. If EC still differs, check calibration and temperature compensation.

EC vs PPM: which should you use?The Grow Pops explanation behind the calculator. → What EC should cannabis seedlings have?Crop-specific guidance for your next question. →

Method and references

Conversions use the selected fixed factor and the unit relationship 1 mS/cm = 1,000 µS/cm. They translate conductivity-based meter displays, not laboratory measurements of nutrient composition.

By Grow Pops. Found a problem? Let us know.