Total Dissolved Solids Calculator

Use the following calculator to calculate Total Dissolved Solids (TDS) from electrical conductivity for any solution. The TDS range covered for this calculator is from 0 to 74,551 mg/L (ppm). Use conductivity range from 0 to 111,900 uS/cm.

Lab Procedure:
1- Measure electrical conductivity (in uS/cm) of sample using conductivity meter at 25 0C
2- Enter electrical conductivity (uS/cm) in the following calculator.
3- Press recalculate button to calculate TDS.

Note: Most types of conductivity meters measure conductivity and make temperature correction at 25 0C. If the equipment you are using does not support temperature correction, then correction should be made manually by calculations according to the manufacturer's procedure.

In another way if you can’t do temperature correction, then you have to measure sample at 25 Celsius degree.

(note: please wait until TDS calculator shows below)

Calculator Performance:
Above calculator has been tested to calculate TDS of several KCl solutions. Results are shown in Table A below:

Table A: TDS calculator performance with different KCl solutions
TDS of KCl Solutions
mg/L (ppm)
Conductivity of Solution at 25 0C (uS/cm) Calculated TDS  using TDS Calculator mg/L (ppm) % Error
0.00 0.0 0.0 0.00
7.46 14.9 7.45 0.16
37.28 73.9 37.27 0.01
74.55 146.9 74.55 0.00
372.76 717.5 372.75 0.00
745.51 1412 767.57 2.96
1491.02 2765 1539.59 3.26
3727.55 6667 3797.01 1.86
7455.10 12890 7488.09 0.44
14910.20 24800 14835.82 0.50
37275.50 58670 37292.27 0.04
74551.00 111900 74549.33 0.00

Questions:

What is TDS stand for?
"Total Dissolved solids" refer to any minerals, salts, metals, cations or anions dissolved in water. This includes anything present in water other than the pure water (H20) molecule and suspended solids. (Suspended solids are any particles/substances that are neither dissolved nor settled in the water, such as wood pulp.)

What’s the measuring unit for TDS?
All units used are represent weight/volume. The most commonly used unit is mg/L (ppm). Another units used is like g/L.

How to measure TDS?
The most accurate method to measure TDS is by measuring electrical conductivity of a solution at 25 Celsius degree, then used calculator above to measure TDS.

How do I know that above calculator is accurate?
Check Table A above it shows a wide range of TDS from 0 - 74,551.0 mg/L. Check percentage of errors in the last column. Highest error you can find is 3.26 % which is still very low <5.

A relation drawn between conductivity and TDS as per Figure A below, to produce two equations of this relation, each of those equation cover specific range of conductivity:

Equation 1:
Cover conductivity between 0 - 717.5 uS/cm and TDS between 0 - 372.76 mg/L (ppm)

TDS mg/L (ppm) = - 0.00000003351240016 x S3
                         + 0.000049948901244919 x S2
                         + 0.500944688449521 x S
                         - 0.00823364899058809

Equation 2:
Cover conductivity > 717.5 - 111,900 uS/cm and TDS between 372.76 - 74,551 mg/L (ppm)

TDS mg/L (ppm) = - 0.000000000005886729 x S3
                         + 0.000001573823009374 x S2
                         + 0.564100864596031 x S
                         - 32.0598990943585

Where
S = Conductivity of solution at 25 Celsius degree (uS/cm)
S2 = Conductivity raised to the power 2
S3 = Conductivity raised to the power 3

Both equations are implemented in above calculator

Reference
Standard Methods for the Examination of Water and Wastewater, 20th edition, 1999.

Figure A: Conductivity vs TDS of KCl solutions