How to use the dilution calculator
- Pick the unknown. Tap C1, V1, C2 or V2 at the top of the calculator. The most common job is V1: how much stock do I need?
- Enter the three values you know. Each line has its own unit menu, so you can type a stock in mM, a target in µM and a final volume in mL without converting anything by hand.
- Read the result and the pipetting step. Below the answer, the dilution calculator spells out how much stock to add to how much diluent, and the overall dilution factor.
If C1 and C2 use different kinds of units (for example a stock in M and a target in mg/mL), an extra field asks for the molecular weight so the calculator can convert between moles and grams. Fold units (10X, 5X, 1X) work too, as long as both concentrations are written in X.
The dilution formula: C1V1 = C2V2
A dilution adds solvent but never adds or removes solute. The amount of solute you pipette out of the stock bottle is exactly the amount that ends up in the new tube, so concentration × volume is the same before and after:
C1 × V1 = C2 × V2
| Symbol | Meaning | Typical units |
|---|---|---|
| C1 | Concentration of the stock solution | M, mM, mg/mL, %, X |
| V1 | Volume of stock you take | L, mL, µL |
| C2 | Concentration you want after diluting | same kind as C1 |
| V2 | Total final volume (stock + diluent) | L, mL, µL |
Rearrange it to solve for any one value: V1 = C2 × V2 ÷ C1, C2 = C1 × V1 ÷ V2, and so on. The LibreTexts chapter on solution dilution derives the same relationship from the number of moles of solute. When the concentrations are molarities, the equation is often written M1V1 = M2V2; our page on the dilution formula walks through the algebra with worked problems.
Two details matter in practice. First, V2 is the total volume, not the volume of water you add: the diluent volume is V2 − V1. Second, both concentrations must be expressed in the same kind of unit before you multiply. That second step is where most hand calculations go wrong, and it is the main reason to use a dilution calculator instead of doing the arithmetic on a sticky note.
C1V1 C2V2 calculator with mixed units
The default example above is a typical cell-culture task: you have a 10 mM stock and need 10 mL of medium at 100 µM. Converting by hand, 10 mM is 10,000 µM, so V1 = 100 µM × 10 mL ÷ 10,000 µM = 0.1 mL. The C1V1 C2V2 calculator does this unit bookkeeping automatically and shows the answer in the unit you chose for the unknown, here 100 µL, followed by the instruction to add it to 9.9 mL of medium.
Supported units:
- Molar: M, mM, µM, nM, pM (each step is a factor of 1,000).
- Mass per volume: g/L, mg/mL, µg/mL, ng/mL, mg/L. Note that 1 mg/mL equals 1 g/L.
- Percent: % is treated as weight per volume (1% = 1 g per 100 mL = 10 mg/mL) whenever it has to be converted to a mass unit. If both C1 and C2 are percentages, the factor cancels, so v/v percentages such as ethanol work as well. See the percent solution dilution calculator for details.
- Fold: X, for buffers sold as 10X or 5X concentrates.
- Volume: L, mL, µL.
Molarity dilution: diluting a stock solution
Most lab dilutions start from a concentrated stock. To prepare a working solution, choose V1 as the unknown, enter the stock molarity as C1, the target molarity as C2 and the volume you need as V2. The molarity dilution result tells you how much stock to pipette; the rest of the final volume is buffer, medium or water.
If you still have to make the stock itself from a powder, start with the stock solution calculator, which turns a target molarity, a volume and a molecular weight into the mass to weigh out. Then come back here to dilute it.
When the result is a very small volume, such as 0.5 µL, it is usually easier to make an intermediate dilution first (for example 1:10) and then dilute that intermediate. The serial dilution calculator plans a whole series of equal steps and lists the concentration in every tube.
Dilution factor and dilution ratios
The dilution factor is the ratio C1 ÷ C2, which is the same as V2 ÷ V1. A 100 µL aliquot made up to 10 mL has a dilution factor of 100. Labs often write this as a ratio such as 1:100, but ratio notation is used in two different ways: some people mean one part sample in 100 parts total, others mean one part sample plus 100 parts diluent. The dilution factor calculator explains both readings and converts between volumes and factors. For cleaning products, garden sprays and other mixes measured in cups and gallons, use the dilution ratio calculator.
Accuracy and limits
Every formula on this site is checked by automated tests that reproduce worked examples from university chemistry texts. Results are shown to six significant figures; round them to the precision of your pipettes and glassware. The dilution calculator assumes that the solute amount is conserved and that the final volume is measured after mixing, which is how volumetric flasks are used. It does not model chemical reactions, mixing of two solutions with different solutes, or temperature effects on volume. Always follow your lab’s protocol and safety data sheets.