TDS ppm to Molarity Converter

Convert Total Dissolved Solids (TDS) in parts-per-million (ppm) to molar concentration (M) for aqueous solutions. Essential for students, researchers, and lab technicians preparing standards, analyzing water quality, or calculating ionic strength. Supports ppm, ppb, ppt units and outputs in M, mM, µM. Fully offline, no data leaves your browser.

Educational only. Follow your lab SOPs and SDS. Verify calculations with calibrated instruments.

Why Convert TDS to Molarity?

Total Dissolved Solids (TDS) in ppm is a common measure in environmental analysis, water treatment, and aquaculture. Converting to molarity (M) is essential for stoichiometric calculations, reaction planning, and comparing ionic strengths. This tool provides the bridge between bulk measurement (ppm) and chemical amount (moles).

Step-by-Step Usage

Enter TDS value – your measured concentration from a conductivity meter or gravimetric analysis.
Select TDS unit – typically ppm (mg/L) for water samples.
Enter molar mass – the formula weight of the dominant solute (e.g., CaCO₃ = 100.09 g/mol for hardness).
Select desired molarity unit – M, mM, or µM for reporting.
Click "Calculate Molarity" – result appears instantly with intermediate steps.

Realistic Examples

Scenario	TDS	Molar Mass	Molarity	Interpretation
Drinking water NaCl	200 ppm	58.44 g/mol	3.42 mM	Low salinity
Seawater Ca²⁺	412 ppm	40.08 g/mol	10.28 mM	Typical calcium level
Lab stock KCl	5000 ppm	74.55 g/mol	67.1 mM	Physiology buffer

Common Mistakes Checklist

Using ppm as molar ppm (rare). This tool uses mass/volume ppm (mg/L).
Forgetting to convert ppb (µg/L) or ppt (ng/L) to base mg/L.
Using atomic weight instead of molecular weight (e.g., Na for NaCl).
Assuming TDS is pure compound; real samples are mixtures (use as approximation).
Ignoring density for non‑aqueous or concentrated solutions.

Quick Molarity ⇄ Mass Converter

Convert between molarity and mass concentration for a single compound.

Molarity (M)

Mass Conc. (g/L)

Molar Mass (g/mol)

Equation: Mass (g/L) = Molarity (M) × Molar Mass (g/mol). Updates live.

Frequently Asked Questions

What are the accuracy limits?

The calculation is mathematically exact for pure solutes. Accuracy depends on your TDS measurement (±2‑5% for conductivity meters) and correct molar mass. For mixtures, treat as an equivalent molarity of the dominant ion.

When does the approximation fail?

At high concentrations (>10,000 ppm) where solution density deviates from 1.00 kg/L, or for mixed electrolytes where the "average" molar mass is unknown. For precise work, use density correction and ion‑specific analysis.

How do I measure TDS in the lab?

Commonly via calibrated conductivity meter (converts to ppm using a factor, often 0.64). For accurate results, use gravimetry: evaporate filtered sample, dry, and weigh residue.

Safety notes for handling standards?

Wear appropriate PPE (gloves, goggles) when preparing concentrated solutions. Consult SDS for the specific compound. Dispose of waste according to institutional regulations.

Formulas & Assumptions

Core formula: Molarity (M) = [TDS (mg/L) ÷ 1000] ÷ Molar Mass (g/mol)

Unit conversions: 1 ppm = 1 mg/L; 1 ppb = 0.001 mg/L; 1 ppt = 1e‑6 mg/L

Output scaling: 1 M = 1000 mM = 1e6 µM

Assumptions: Aqueous solution density = 1.000 kg/L; TDS is entirely the specified compound.

Rounding: Results shown to 4 significant figures; internal calculations use double precision.

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TDS ppm to Molarity Converter

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