Sigma Aldrich Dilution Calculator
Diluting a stock solution is the most common calculation in a wet lab: you have a concentrated stock, you need a weaker working solution, and you need to know exactly how much stock to pipette. This dilution calculator works like the Sigma-Aldrich tool: enter any three of the four values (stock concentration C1, stock volume V1, final concentration C2, final volume V2) and it solves the fourth with C1 x V1 = C2 x V2, then gives you the diluent volume and a step-by-step bench protocol.
Dilution Calculator (C1V1 = C2V2)
Enter any three values. Leave the one you want to solve completely empty.
The dilution formula
Every dilution follows one conservation rule: the amount of solute you put in equals the amount you end with. Concentration times volume before dilution equals concentration times volume after:
C1 x V1 = C2 x V2
Rearranged to solve for the stock volume, which is what most bench work needs:
V1 = (C2 x V2) / C1
The calculator above also solves for V2, C1, or C2. Just leave that field empty. The diluent volume is then the difference: diluent = V2 - V1.
Worked example
You have a 10X stock buffer and need 100 mL of a 1X working solution:
V1 = (1 X x 100 mL) / 10 X = 10 mL of stock. Diluent = 100 - 10 = 90 mL. This is a 10-fold (1:10) dilution. Pipette 10 mL of the 10X stock, add 90 mL of water or buffer, mix, and you have 100 mL of 1X solution.
Second example, molar units: 250 mL of 0.5 M from a 2 M stock. V1 = (0.5 x 250) / 2 = 62.5 mL of stock; diluent = 250 - 62.5 = 187.5 mL. A 4-fold (1:4) dilution. Run both in the tool above and the protocol, diluent, and factor all agree.
Common lab dilutions at a glance
| Dilution | Stock needed | Diluent | Example (100 mL final) |
|---|---|---|---|
| 1:2 (2-fold) | 50% of final volume | 50% of final volume | 50 mL stock + 50 mL diluent |
| 1:5 (5-fold) | 20% of final volume | 80% of final volume | 20 mL stock + 80 mL diluent |
| 1:10 (10-fold) | 10% of final volume | 90% of final volume | 10 mL stock + 90 mL diluent |
| 1:100 (100-fold) | 1% of final volume | 99% of final volume | 1 mL stock + 99 mL diluent |
What competing dilution tools miss
The official Sigma-Aldrich calculator and its clones solve the equation but stop at the numbers. Ours also prints a bench-ready protocol ("pipette X, add Y, mix"), shows the dilution factor (1:10) on every result, and warns you when the numbers imply a negative diluent volume. A negative diluent means C1 and C2 were swapped, the single most common beginner mistake, and most tools will silently hand you an impossible answer.
Frequently asked questions
Do the concentration units have to match?
Yes. C1 and C2 must be in the same unit (both M, both mg/mL, both X), and V1 and V2 must be in the same unit (both mL, both uL). The calculator checks this and warns you instead of giving a wrong answer. To convert between units first, convert mg/mL to M using the compound's molecular weight, or use 1 M = 1000 mM = 1,000,000 uM and 1 L = 1000 mL = 1,000,000 uL.
What is a dilution factor?
The dilution factor is C1 / C2, the ratio of stock to final concentration. A 10X stock diluted to 1X has a factor of 10, called a 1:10 dilution. It tells you what fraction of the final volume is stock: 1/10 of the final volume is stock, the rest is diluent.
Can I use this for serial dilutions?
Yes, run one step at a time. For a 1:10 serial series, calculate the first dilution, then treat its product as the stock (C1) for the next step. Each 1:10 step multiplies the dilution factor by 10: after 3 steps a 10 mM stock becomes 10 uM.
Why does the calculator say the diluent volume is negative?
The math says you need more stock than the final volume allows, which is physically impossible. You almost certainly swapped C1 and C2: the stock concentration must be the larger number. Swap them and recalculate.
Does this work for percent solutions?
Yes, select % for both concentrations. A 10% stock diluted to 2% is a 5-fold dilution: V1 = (2 x V2) / 10. Note that % to M conversions need the molecular weight, so keep both values in the same unit.