Softonic

Dilution Calculator

Step 1 / 3 Stock volume needed
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A dilution calculator solves the classic C₁V₁ = C₂V₂ equation so you can mix a concentrated stock down to a working concentration without guesswork. Enter the stock concentration, the desired concentration and the final volume you need, and it returns the exact volume of stock to pipette, how much diluent (water or buffer) to add, and the resulting dilution factor. It is built for lab bench prep, buffers, reagents, cell-culture media and chemistry homework.

How to dilute a stock solution

  1. 1

    Enter stock and target concentration

    Both must use the same units (M, mM, mg/mL, %, etc.). The target must be lower than the stock.

  2. 2

    Enter the final volume

    The total volume you want after mixing, in mL.

  3. 3

    Read the result

    Stock volume to use, diluent to add, and the dilution factor (e.g. 10× means a 1-in-10 dilution).

The dilution equation

The calculator rearranges the conservation-of-moles relationship:

C₁ × V₁ = C₂ × V₂

where:

  • C₁ = concentration of the stock (starting) solution
  • V₁ = volume of stock to use (the unknown you usually solve for)
  • C₂ = desired final concentration
  • V₂ = desired final volume

Solving for the stock volume:

V₁ = (C₂ × V₂) ÷ C₁

The diluent you add is simply V₂ − V₁, and the dilution factor is C₁ ÷ C₂.

The concentration units cancel, so any consistent unit works (M, mM, µM, mg/mL, % w/v) as long as C₁ and C₂ share it.

Worked example

You have a 10 M stock of NaOH and you need 100 mL of a 1 M working solution.

  • V₁ = (1 × 100) ÷ 10 = 10 mL of stock.
  • Diluent to add: 100 − 10 = 90 mL.
  • Dilution factor: 10 ÷ 1 = 10× (a 1-in-10 dilution).

So you measure 10 mL of the 10 M stock and bring it up to 100 mL with water.

Quick reference

Stock Target Final volume Stock to use Diluent Factor
10 M 1 M 100 mL 10 mL 90 mL 10×
100× 1× 50 mL 0.5 mL 49.5 mL 100×
5 mg/mL 0.5 mg/mL 20 mL 2 mL 18 mL 10×
2 M 0.25 M 250 mL 31.25 mL 218.75 mL 8×

Common pitfalls

  • Target above stock is impossible. You cannot make a solution more concentrated by adding diluent. This tool clamps the target to the stock and flags it.
  • Mixed units. C₁ and C₂ must match. Converting M to mM (×1000) before entering avoids silent errors.
  • Add stock to diluent, not the reverse, especially for acids. For concentrated acids, always add acid to water to dissipate heat safely.
  • Top up to the final mark. Add stock first, then bring the volume up to V₂; do not add the full diluent volume on top of the stock.

Frequently Asked Questions

It is the ratio of stock to final concentration (C₁ ÷ C₂). A factor of 10 means a 1-in-10 dilution: one part stock plus nine parts diluent. A factor of 100 is a 1-in-100 dilution, and so on.

Yes, as long as the stock and target use the same unit. Molarity (M, mM, µM), mass per volume (mg/mL), and fold concentrates (10×, 100×) all work because the units cancel in C₁V₁ = C₂V₂.

If you ask for a target concentration that is higher than the stock, dilution cannot achieve it. The calculator flags this case and limits the stock volume so the math stays physically sensible rather than returning a negative diluent.

Repeat the dilution step by step. For a 1:10 serial dilution, take the result of one dilution as the stock for the next: 1 mL of solution into 9 mL of diluent each time. Use this calculator once per step.

Yes. The values are sent to our server to run the calculation as you type, and in the multi-step view they also travel in the page link as you advance. They are not saved in our database. Enter only values you are comfortable sending over the internet.

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