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Dilution Calculator

A dilution lowers the concentration of a stock solution by adding diluent. Enter the stock concentration and a dilution factor to get the final concentration, or enter two concentrations to get the factor, or a factor and a final volume to get exactly how much stock to transfer and how much diluent to add. Because a dilution depends only on a ratio, the concentration unit can be anything — M, %, mg/mL or CFU/mL — as long as both sides use the same one.

Diluting a stock is one of the most repeated actions in any lab, and the part people get wrong is rarely the arithmetic — it is the meaning of "1:10". Does that mean one part stock plus ten parts diluent, or one part stock in a total of ten? This calculator uses the convention that matters at the bench: a **1:10 dilution has a dilution factor of 10**, which is 1 part stock plus 9 parts diluent for 10 parts total. It is part of our laboratory calculator set, and it pairs directly with the C1V1 calculator when you would rather think in concentrations and volumes than in factors.

The other thing that surprises people is that dilution maths is unit-blind. Halving a 4 M solution, a 20% sucrose solution or a culture at 1 × 10⁹ CFU/mL all use the same factor of 2. That is why this tool does not force your concentration into molarity the way the molarity calculator does — you enter the number off the bottle and the unit rides along for the answer.

Any unit — M, %, mg/mL or CFU/mL. Only the ratio to the final concentration matters.

A 1:10 dilution has a factor of 10 (1 part stock + 9 parts diluent).

Final concentration0.1
Dilution factor10 ×
Ratio (stock : diluent)1 : 9
Stock volume10 mL
Diluent volume90 mL

How to use the dilution calculator

Choose what you are solving for in the **Solve for** dropdown. "Final concentration" starts from a known stock and a factor; "Dilution factor" starts from two concentrations; "Stock and diluent volumes" starts from a factor and the total volume you want to end up with.

Enter the **stock concentration** exactly as labelled. You do not need to convert % to molar or mg/mL to M — just keep the final concentration in the same unit so the ratio is meaningful.

For the volume modes, enter the **final volume** you want and pick its unit (L, mL or µL). The calculator converts to litres internally, then reports how much stock to pipette and how much diluent to add to reach that total.

Press **Calculate**. The primary card answers your question; the secondary cards always show the dilution factor, the "1 part stock : N parts diluent" ratio, and the stock and diluent volumes when you supplied a final volume.

Dilution formula

DF = C₁ / C₂
DF = V_final / V_stock
C₂ = C₁ / DF
V_stock = V_final / DF
V_diluent = V_final − V_stock
DF = dilution factor (×) · C₁ = stock concentration · C₂ = final concentration (same unit as C₁) · V_final = total volume after dilution · V_stock = aliquot of stock transferred

Variables and units

SymbolMeaningUnit
DFDilution factor×
C₁Stock (starting) concentrationany
C₂Final (diluted) concentrationsame as C₁
V_finalTotal volume after dilutionL
V_stockVolume of stock transferredL
V_diluentVolume of diluent addedL

How dilution is calculated

  1. Write the dilution factor as a ratio: DF = stock concentration ÷ final concentration, or final volume ÷ stock volume.
  2. To find a final concentration, divide the stock by the factor: C₂ = C₁ ÷ DF.
  3. To find volumes from a factor, divide the final volume by the factor to get the stock aliquot: V_stock = V_final ÷ DF.
  4. Subtract to get the diluent: V_diluent = V_final − V_stock. Add the stock to the diluent (or make up to the mark) to reach the final volume.

Worked laboratory examples

Example 1 — A 1:10 dilution of a 5× buffer

Given: stock 5× · dilution factor 10 · final volume 100 mL

  1. C₂ = 5 ÷ 10 = 0.5×
  2. V_stock = 100 mL ÷ 10 = 10 mL
  3. V_diluent = 100 − 10 = 90 mL

Result: 0.5× working buffer — mix 10 mL of 5× stock with 90 mL of water

Example 2 — Finding the factor between two concentrations

Given: stock 2 mg/mL · final 0.05 mg/mL

  1. DF = 2 ÷ 0.05 = 40
  2. ratio = 1 part stock : 39 parts diluent

Result: a 1:40 dilution (factor 40)

Example 3 — Volumes for a 1:5 dilution of 250 mL

Given: dilution factor 5 · final volume 250 mL

  1. V_stock = 250 ÷ 5 = 50 mL
  2. V_diluent = 250 − 50 = 200 mL

Result: pipette 50 mL of stock into 200 mL of diluent

How to interpret the result

A dilution factor of 10 means the final solution is one tenth as concentrated as the stock, whatever the unit. The "1 part stock : 9 parts diluent" line is the practical translation — it tells you the ratio to pipette without committing to a total volume, which is handy when you only need "some" of a working solution.

If the factor comes out below 1, the calculator warns you: a factor under 1 means the "diluted" number is actually stronger than the stock, which almost always means the two concentrations were entered the wrong way round. Factors above a million are mathematically fine but practically a sign that you should do a serial dilution in several steps rather than one huge jump.

Assumptions

  • Volumes are additive — the final volume equals stock volume plus diluent volume.
  • The solute is conserved through the dilution: nothing reacts, binds, precipitates or is lost.
  • Stock and final concentration are expressed in the same unit so the ratio is dimensionless.

Limitations

  • Concentrated stocks in aqueous diluent can show small non-additive volume effects; for analytical precision make up to a volumetric mark rather than summing aliquots.
  • The calculator does not plan multi-step serial dilutions — for a 1:10,000 factor it reports the single-step answer, not the series of tubes you would actually use.
  • It does not check solubility or stability; a factor is valid maths even when the diluted species would fall out of solution.

Common mistakes

  • Reading "1:10" as 1 part stock in 10 parts diluent (a factor of 11). In this tool 1:10 is a factor of 10 — 1 part stock plus 9 parts diluent.
  • Mixing concentration units between stock and final, for example stock in M and final in mM, then treating the raw numbers as a ratio.
  • Adding the stock to a fixed volume of diluent instead of making up to the final total volume — 10 mL stock + 100 mL water is a 1:11 dilution, not 1:10.
  • Attempting a very large single-step dilution with a pipette volume below its accurate range; serial steps are more accurate.

FAQ

What does a 1:10 dilution mean?

It means a dilution factor of 10: one part of stock brought to ten parts total, which is 1 part stock plus 9 parts diluent. The final concentration is the stock concentration divided by 10. This calculator uses that total-volume convention.

How do I calculate a dilution factor?

Divide the starting concentration by the final concentration (DF = C₁ / C₂), or divide the final total volume by the volume of stock you used (DF = V_final / V_stock). A stock of 2 mg/mL diluted to 0.05 mg/mL has a factor of 40.

Is dilution factor the same as C1V1?

They describe the same dilution. C1V1 = C2V2 solves for an unknown concentration or volume directly, while the dilution factor is the single ratio C1/C2 = V2/V1. Use the dilution factor when you think in "1:X" terms and the C1V1 calculator when you have specific concentrations and volumes.

Does the concentration unit matter?

No, as long as the stock and the final concentration use the same unit. A dilution is a ratio, so M, %, mg/mL and CFU/mL all behave identically. The answer comes back in whatever unit you entered.

How much stock do I add for a given final volume?

Divide the final volume by the dilution factor. For 100 mL at a factor of 10, transfer 10 mL of stock and add diluent to 100 mL total — which means 90 mL of diluent. The calculator reports both numbers.

When should I use a serial dilution instead?

When the factor is so large that the single-step stock volume would be smaller than your pipette can accurately deliver. A 1:10,000 dilution is more reliable as four successive 1:10 steps than as one 1 µL into 10 mL jump.

Scientific Sources

External links open in a new tab and carry rel="nofollow". We cite primary references (NIST, NIH/NCBI, peer-reviewed papers) and established manufacturer technical documentation (NEB, Thermo Fisher, Promega, IDT). Calculated results are estimates; your protocol and manufacturer guidance take precedence.

Last reviewed: 2026-09 · Method version: 1.0