Free Calculator · Published October 2026
TDS Constituent Sum: Add the Ions on the Lab Sheet
This TDS constituent sum adds the dissolved ions you actually have. Leave the rest blank so they are not pretended into the total.
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Book a DemoA TDS Constituent Sum Is Only the Lines You Type
The ion list comes from the U.S. Geological Survey description of what typically makes up most dissolved solids. The public 500 mg/L guideline is explained in TDS in well water. Why a meter is not this sum is conductivity and TDS.
Leave a box blank when that line is not on the sheet. Zero means the lab reported zero.
Important: All calculator results are ballpark estimates
All calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements.
What the TDS Constituent Sum Is Using
Nine names, and only the ones present
USGS says those nine typically make up most of the dissolved solids. “Most” is not a promise that every sheet has all nine, and it is not a promise that nothing else is dissolved. A blank box is excluded. A zero is included. That is the whole formula: addition, in milligrams per liter, of the lines you typed.
Worked examples
Same addition as the form. The second case leaves potassium, chloride, nitrate, and silica blank, so they are not inside the 205.
| Case | Ions used | Partial sum |
|---|---|---|
| Sodium and chloride only | 2 | 100 mg/L |
| Five ions, four left blank | 5 | 205 mg/L |
Do not convert inside the box
Bicarbonate means bicarbonate. If the lab printed alkalinity as calcium carbonate, leave bicarbonate blank or convert somewhere else and write that you did. Nitrate should be one basis for the whole sum. The nitrate unit converter is nitrate only. Hardness as grains does not belong in the calcium box. The how to test water hardness page is the hardness method. This sum will not turn grains into milligrams for you.
What to write on the job ticket
The partial sum, how many of the nine lines you had, and which were blank. Say it is not the lab total unless the lab total is a separate number you also wrote down. A water treatment dealer can keep both numbers on the customer record. Compare either one to the public 500 mg/L guideline only after you have said which method produced it. If the lab already printed a dissolved-solids total, write that total beside this addition and do not replace it. Lines reported as calcium carbonate need a conversion this form does not do, so leave them blank until the units match.
Frequently Asked Questions
What does a TDS constituent sum add?
It adds the milligrams per liter you type for calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride, nitrate, and silica. The U.S. Geological Survey says those constituents typically make up most of the dissolved solids in water. Blank lines are left out. The total is a partial sum, not a laboratory total dissolved solids result.
Is this the same as a TDS lab method?
No. A residue method dries a sample and weighs what remains. This page only adds numbers you already have. If an ion is missing, the sum is incomplete on purpose. Do not relabel it as the lab total.
Should bicarbonate be entered as alkalinity?
Only if the sheet already says bicarbonate in milligrams per liter. Alkalinity as calcium carbonate is a different reporting basis. This TDS constituent sum does not convert alkalinity into bicarbonate.
Does the tool convert conductivity into TDS?
No. Specific conductance is a surrogate. The USGS page used here does not print a single multiplier, and this calculator does not invent one. A meter reading stays a meter reading.
What if nitrate is reported as nitrogen?
Convert it before you type it, and say which basis you used. Mixing nitrate-nitrogen with ions that are already the full ion makes the sum inconsistent. The nitrate unit converter on this site uses 4.43 for nitrate only, not for nitrite.
Keep the Partial Sum With the Lab
The ions you had, the ones you did not, and the lab total if it exists should sit on the same job.
Get a Free DemoAll calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements. The partial sum is not a measured total dissolved solids result.