Dilution calculator
Fill any three of the four values. The fourth is solved as you type.
Stock
Final
Fill any three of the four values. The fourth is solved as you type.
Diluting a solution changes its volume but not the amount of solute in it. Amount is concentration times volume, so the amount in the stock you take out, C₁V₁, equals the amount in the final solution, C₂V₂. Knowing any three of the four values fixes the fourth, and that one relation covers every routine dilution: a drug from a DMSO stock, a primer from 100 µM to 10 µM, a 10× buffer to 1×, or an antibody at 1:1000.
Worked example. You have a 10 mM stock and need 1 mL of 1 mM. V₁ = 1 mM × 1 mL ÷ 10 mM = 0.1 mL. Pipette 100 µL of stock into 900 µL of diluent. The dilution factor is C₁ ÷ C₂ = V₂ ÷ V₁ = 10, a 1:10 or 10-fold dilution.
Volumes of a few microlitres are hard to pipette accurately. If the calculator asks for less than about 2 µL of stock, make an intermediate dilution first, or plan the whole series with the serial dilution planner.
The dilution factor is how many times more dilute the final solution is than the stock, C₁ ÷ C₂, which is also V₂ ÷ V₁. A 10-fold dilution, 1:10 and "1 in 10" all mean one part stock in ten parts total. Beware the older convention, still used in some clinical work, in which 1:10 means one part stock plus ten parts diluent, an 11-fold dilution. When a protocol gives a ratio, check which convention it uses; when you write one, prefer "10-fold".
Concentrated buffers and media supplements are labelled by fold: a 10× stock is ten times the working strength. Bringing 10× to 1× is a plain 10-fold dilution, and the Fold tab does that arithmetic without needing any concentration units at all.
Molar units (M, mM, µM, nM, pM) count molecules; mass units (mg/mL, µg/mL, ng/µL, ng/mL) weigh them; percent is grams per 100 mL or millilitres per 100 mL. The dilution equation works within any one family, because the units cancel, but not across families: converting mg/mL to mM needs the molecular weight. Use the molarity calculator to convert the stock first. Note that ng/µL and µg/mL are the same concentration, and the calculator treats them so.
| Task | Typical dilution |
|---|---|
| Primer working stock | 100 µM → 10 µM, 10-fold |
| 10× PCR or running buffer | 10× → 1×, 10-fold |
| Primary antibody for a western | 1:1000 in blocking buffer |
| Drug from a 10 mM DMSO stock | to 10 µM, 1000-fold, often in two steps |
| Bacterial culture for plating | 10-fold series, 10⁻¹ to 10⁻⁸ |
Antibody dilutions are usually stated as ratios rather than concentrations; theantibody dilution calculator turns a 1:x ratio and a final volume straight into microlitres.
Use C1V1 = C2V2. Multiply the final concentration by the final volume and divide by the stock concentration to get the volume of stock to take; the rest of the final volume is diluent. To make 1 mL of 1 mM from a 10 mM stock: V1 = 1 mM × 1 mL ÷ 10 mM = 0.1 mL, so 100 µL of stock plus 900 µL of diluent.
In most laboratory usage they mean the same thing: one part stock in ten parts total, a 10-fold dilution. Some fields, chiefly clinical and older microbiology texts, read 1:10 as one part stock to ten parts diluent, which is an 11-fold dilution. State the dilution factor as a number, 10×, when it matters.
Only if you know the molecular weight, because mass and molar units measure different things. Convert the stock to molar first with the molarity calculator, then dilute. The calculator warns if the stock and final concentrations are in different unit families.
Because the final concentration is higher than the stock. A dilution can only lower concentration. Either the numbers are swapped, or you need a more concentrated stock, or you need to concentrate the sample instead.
Use the Fold tab: a 10× stock brought to 1× is a 10-fold dilution, so take one tenth of the final volume as stock and make up the rest with water. For 500 mL of 1× buffer that is 50 mL of 10× stock plus 450 mL of water.