Calculators
Dilution
Work out how much stock solution to take for a target concentration and final volume, and plan a serial dilution. Everything is calculated in your browser.
Serial dilution planner
| Tube | Concentration | Transfer from previous | Diluent |
|---|
Each tube is made up to the full volume; once the transfer is drawn, intermediate tubes are short by that amount. Only the last tube keeps the full volume.
Formula
C₁ × V₁ = C₂ × V₂
- C₁
- concentration of the stock solution
- V₁
- volume of stock to take — the unknown
- C₂
- target final concentration
- V₂
- final volume of the solution
Worked example
Making 1 ml of antibody at 50 µg/ml from a 10 mg/ml stock
- C₁ = 10 mg/ml
- C₂ = 50 µg/ml = 0.05 mg/ml
- V₂ = 1 ml
- Put both concentrations in the same unit family: 50 µg/ml is 0.05 mg/ml.
- Rearrange for V₁: V₁ = C₂ × V₂ ÷ C₁
- Substitute: V₁ = 0.05 × 1 ÷ 10 = 0.005 ml
- Diluent is final volume minus stock volume: 1000 − 5 = 995 µl
Answer 5 µl of stock + 995 µl of diluent — a 1 in 200 dilution
Common mistakes
- Mixing a mass unit with a molar unit in one calculation. Converting mg/ml to µM is impossible without a molecular weight, so this tool warns instead of returning a meaningless number.
- Adding the final volume of diluent rather than the difference. Adding 1000 µl to 5 µl of stock gives 1005 µl and a concentration below target.
- Pipetting below one microlitre. Relative error at those volumes is large — make an intermediate dilution or scale the final volume up instead.
- Forgetting that in a serial dilution each intermediate tube loses the transferred volume. Only the last tube keeps its full volume.
Frequently asked
What if the final concentration is higher than the stock?
Dilution cannot raise a concentration, so there is no physical answer and the tool warns you. You would need a more concentrated stock, or to concentrate the solution.
What do the X and per-cent units mean?
X expresses how many times more concentrated something is than its working strength — a 10X buffer is diluted tenfold. Per cent is usually weight per volume, so one per cent is one gram in 100 ml. Both are relative and cannot be combined with molar or mass units.
What dilution factor should a serial dilution use?
Standard curves usually use tenfold or twofold steps. Tenfold covers a wider range; twofold gives finer resolution over a narrow one. Choose a tube volume that keeps the transfer above about twenty microlitres.