Enrichment · Passion Projects · Lab skills

How much stock,
how much water,
to hit the strength you need.

Type three of the four: stock strength, stock volume, final strength and final volume. The calculator solves the fourth and tells you how much diluent to add.

Work out a dilutionWhat you get

The dilution calculator

The worked example makes 500 mL of 70% ethanol from a 95% stock. Nothing you type leaves this browser.

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What you get

Enrichment · Passion ProjectsFree

What you finish with
The missing value, the stock and diluent volumes, the dilution as 1 in N, and a tenfold serial dilution table. It prints as a summary and downloads as a spreadsheet.
Who it is for
Biology and chemistry students, teachers preparing lab solutions, and science fair students working with dilutions.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Passion Projects space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Choose the concentration and volume units.
  2. Fill in three of the four values and leave the one you want blank.
  3. Read the stock and diluent volumes.
  4. Use the serial table for very large dilutions.
  5. Print the summary for the bench.

Work out a dilution

How the dilution is worked out

The solute you take is the solute you end with.

The worked example: 70% ethanolSolute wanted70% × 500 mL= 350 mL of ethanolStock is 95%368.42 mL350 ÷ 0.95Diluent≈ 131.58 mLwater up to 500 mLDilution1 in 1.3695 ÷ 70The worked example: 70% ethanolSolute wanted70% × 500 mL= 350 mL of ethanolStock is 95%368.42 mL350 ÷ 0.95Diluent≈ 131.58 mLwater up to 500 mLDilution1 in 1.3695 ÷ 70
Diluting changes the volume, not the amount of solute. Whatever solute is in the stock you take ends up spread through the final volume.

The arithmetic

C1 × V1 = C2 × V2, where C1 and V1 are the stock's concentration and the volume of it you use, and C2 and V2 are the final concentration and volume. Any one can be solved from the other three. The diluent is V2 − V1, and the dilution factor C1 ÷ C2 is often written 1 in N. Both concentrations must use the same unit, and both volumes.

At the bench

Pipettes are most accurate in their middle range, so dilutions beyond about 1 in 100 are better done in two steps. A serial dilution repeats 1 part plus 9 parts diluent to step down tenfold each time, as in plate counts. Alcohol and water shrink slightly when mixed, so make up to the final volume instead of adding the two volumes together.

Sources

  1. IUPAC. Compendium of Chemical Terminology (the Gold Book): dilution and amount concentration (goldbook.iupac.org).
  2. Centers for Disease Control and Prevention. Laboratory training: serial dilutions and dilution factors (cdc.gov).
  3. National Institute of Standards and Technology. NIST Chemistry WebBook: ethanol and ethanol-water mixtures (webbook.nist.gov).
  4. American Chemical Society. Guidelines for Chemical Laboratory Safety in Secondary Schools (acs.org).

The worked example is made up. Follow your school's lab safety rules. Your figures stay in this browser. Support: team@caveatacademic.com.