Molarity Calculator
Enter the molecular weight from your reagent bottle, choose your desired concentration and volume, and this calculator will tell you exactly how much powder to weigh out.
Parameters
Use the MW printed on your reagent — it will already account for the hydration state and salt form.
Result
| Parameter | Value |
|---|---|
| Molecular weight | 58.44 g/mol |
| Target concentration | 1.0000 M |
| Volume | 100 mL (0.1000 L) |
| Moles needed | 0.100000 mol |
| Mass to weigh | 5.8440 g |
About Molarity Calculations
Molarity (M) is defined as moles of solute per litre of solution. It is the standard unit of concentration in chemistry and biology labs. To prepare a solution of known molarity from a dry reagent, you need the molecular weight (MW) of the compound, the target concentration, and the desired final volume.
The Equation
Weigh out the calculated mass, dissolve in slightly less than the target volume of solvent, then make up to the final volume once fully dissolved. This ensures accurate concentration.
Watch the MW on the Label
Always use the MW printed on your specific reagent bottle. For example, Tris base (MW 121.14) and Tris-HCl (MW 157.60) are different. EDTA is commonly sold as the disodium dihydrate salt (MW 372.24), not the free acid (MW 292.24). MgCl₂ is usually the hexahydrate (MW 203.30), not anhydrous (MW 95.21). Using the wrong MW is one of the most common causes of incorrect solution concentration.
Relevance to Microfluidics
Microfluidic experiments typically consume very small volumes (microlitres) but require precise concentrations for reproducible results. Preparing accurate stock solutions off-chip is critical because even small errors in concentration can significantly affect assay performance in channels where mixing volumes are measured in nanolitres. Where possible, prepare a concentrated stock and dilute down — this minimises weighing errors for small masses.
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