Q&A for How to Calculate Total Dissolved Solids

To measure liquid, pour it in a beaker or graduated cylinder. Then measure with the bottom of the meniscus, which is the curved upper surface of a liquid in a tube.

Note how much the water level has risen. The amount displaced will be in direct relation to the amount dissolved.

If you have a RO system, the TDS meter reading should be over 90%. (Tap water TDS minus RO TDS) divided by tap water TDS. Should equal over 90%, if not, replace the membrane. My Reverse Osmosis TDS is usually 11. You want it to be a smaller number. Bottled water with minerals added will have a different reading because the TDS meter will count the minerals added to the water, so you will not get an accurate reading.

If you know that mass of solute in solution, follow these steps. Simply pass a known voltage through the solution and measure the current. Calculate the resistance (V/I=R), then follow these steps. (1) Conductance (G) = 1/R, (2) k = ((mass/(G*0.6475))/2) x 0.6475, TDS = G x k.