labmatetools / 2.3 MOLARITY ALL TOOLS

Molarity Calculator

How much to weigh for a molar solution, what molarity you made, or how to read mg/mL as µM. Enter the molecular weight once and use it for both.

SECTION 02 — CALCULATORS · 2.3ENTER → CONVERT → WEIGH

MMOLECULAR WEIGHT

COMMON REAGENTS

Use the formula weight on your bottle. Hydrates weigh more: MgCl₂ is 95.21 g/mol, MgCl₂·6H₂O is 203.30 g/mol.

SOLVE FOR
cCONCENTRATION
VFINAL VOLUME
mMASS TO WEIGH
ANSWER

RECIPE
  1. WEIGH—
  2. DISSOLVE IN—
  3. MAKE UP TO—
  4. GIVES—

CONVERT A CONCENTRATIONMASS / VOLUME ↔ MOLAR · USES M ABOVE

cYOU HAVE

MOLAR
MASS / VOLUME
ABOUT THIS TOOL

How to use

  1. Enter the molecular weight, or tap a common reagent. For a protein, switch the unit to kDa.
  2. Under SOLVE FOR, pick MASS to find how much to weigh. Pick CONC. to find the molarity of what you weighed, or VOLUME to find how far to make it up.
  3. Fill in the other two boxes. Units can be mixed — mM with mL, µM with µL.
  4. The recipe follows the usual bench method: dissolve in about 80% of the final volume, then make up to the mark.
  5. To read a stock labelled in mg/mL or ng/µL as µM (or the other way), use Convert a concentration below. It uses the same molecular weight.
  6. Need to dilute the stock you just made? Go to the Dilution tool.

The formula

m = c × V × M
mmass in grams
cconcentration in mol/L (M)
Vfinal volume in litres
Mmolecular weight in g/mol

Mass concentration (g/L) = molarity (M) × M. 1 mg/mL = 1 g/L. 1% w/v = 10 g/L.

Example. 500 mL of 1 M NaCl (58.44 g/mol): m = 1 mol/L × 0.5 L × 58.44 g/mol = 29.22 g.

Good to know

  1. Free to use. No subscription. Nothing you type leaves your browser.
  2. Masses under about 1 mg are hard to weigh well. Make a more concentrated stock and dilute it.
  3. Results are rounded to 4 significant figures.
  4. A calculator, not a protocol: check solubility and your own method.
QUESTIONS · MOLARITY CALCULATOR

Frequently asked

How many grams do I need to make a molar solution?

Mass = concentration × volume × molecular weight. For 500 mL of 1 M NaCl (58.44 g/mol): 1 mol/L × 0.5 L × 58.44 g/mol = 29.22 g.

How do I convert mg/mL to µM?

Divide the mass concentration (1 mg/mL = 1 g/L) by the molecular weight to get molarity. Use Convert a concentration on the page; it uses the same molecular weight.

Which molecular weight should I use for a hydrate?

Use the formula weight on your bottle. Hydrates weigh more: MgCl₂ is 95.21 g/mol, MgCl₂·6H₂O is 203.30 g/mol.

Can I use it for a protein?

Yes. Switch the molecular weight unit to kDa.