Last updated: 2026-06-14

What dilution means

Diluting a solution means adding more solvent to lower its concentration. The amount of solute stays the same — only the volume increases — so the solution becomes weaker. Dilution is one of the most common bench operations in chemistry and biology, used to prepare working solutions from concentrated stocks.

The dilution formula

The equation works because the product $C \times V$ equals the number of moles of solute, and that number does not change when you add pure solvent. Rearrange it to solve for whichever quantity you need:

• Stock volume to take: $V_1 = \dfrac{C_2 V_2}{C_1}$
• Final concentration: $C_2 = \dfrac{C_1 V_1}{V_2}$
• Final volume: $V_2 = \dfrac{C_1 V_1}{C_2}$

Worked example

You have a 1 M stock of hydrochloric acid and need 500 mL of 0.2 M HCl. How much stock do you take?

Measure 100 mL of the 1 M stock, then add water up to a final volume of 500 mL — adding about 400 mL of water.

Add solvent to the mark, not by volume

Because mixing can change the total volume slightly, the reliable method is to add the measured stock to a volumetric flask and then top up with solvent to the final-volume calibration line. The "solvent to add" figure (V₂ − V₁) is a useful estimate, but the final volume mark is what defines the concentration.

Dilution factor

The dilution factor is the ratio of final to initial volume, or equivalently the ratio of stock to final concentration:

A 1:10 dilution (dilution factor 10) means one part stock and nine parts solvent, giving a solution ten times weaker. When a single dilution would need impractically small volumes, chemists use a serial dilution — repeating a modest dilution several times. Each step multiplies the dilution factor, so three 1:10 steps give a 1:1000 dilution overall.

Common uses

• Preparing working concentrations of acids, bases, and buffers from concentrated stocks.
• Making standard curves for spectrophotometry by serial dilution.
• Diluting cell-culture media, antibiotics, and reagents in biology labs.