Serial Dilution Calculator
Concentration at every tube in a serial dilution.
After 6 serial 10-fold dilutions.
| Tube | Dilution | Concentration (µg/mL) |
|---|---|---|
| 0 | 1:1 (stock) | 1000 |
| 1 | 1:10 | 100 |
| 2 | 1:100 | 10 |
| 3 | 1:1000 | 1 |
| 4 | 1:10000 | 0.1 |
| 5 | 1:100000 | 0.01 |
| 6 | 1:1000000 | 0.001 |
In a serial dilution, each tube divides the previous one by a fixed factor, so the concentration of tube n is Cₙ = C₀ ÷ factorⁿ. Starting from 1,000 µg/mL with a 10-fold factor, six steps give 1,000 ÷ 10⁶ = 0.001 µg/mL — a million-fold dilution in six manageable steps.
How a serial dilution works
A serial dilution repeats the same dilution step over and over to span many orders of magnitude — the backbone of standard curves, plate counts, and titrations. Each tube is the previous tube divided by a fixed dilution factor, so the concentration drops geometrically: after n steps it has been divided by the factor n times.
C₀ = stock concentration, n = tube number (0 = stock)
Worked example
Stock of 1,000 µg/mL, a 10-fold dilution factor, six steps:
- 1 Start from the stock (tube 0). C₀ = 1,000 µg/mL, dilution 1:1.
- 2 Apply one 10-fold step. Tube 1 = 1,000 ÷ 10 = 100 µg/mL (1:10).
- 3 Keep dividing by the factor. Tube 2 = 10, tube 3 = 1, tube 4 = 0.1, tube 5 = 0.01 µg/mL.
- 4 Read the final tube. Tube 6 = 1,000 ÷ 10⁶ = 0.001 µg/mL — a million-fold dilution reached in six manageable steps.
Why serial, the bench mechanics, and pitfalls
Why not dilute in one step. Pipetting a 1,000,000-fold dilution directly is wildly inaccurate — you’d transfer a microscopic volume into a huge one. Six 10-fold steps reach the same endpoint with far less error because every transfer is a comfortable volume.
How to hit a given factor. For a 10-fold step, move 1 part sample into 9 parts diluent (factor = (1 + 9) ÷ 1 = 10). For a 2-fold step, mix equal volumes.
Common mistakes. Mix each tube thoroughly before drawing the next transfer, and use a fresh tip every step — carryover on a reused tip inflates the downstream concentrations. Remember tube 0 is the undiluted stock, so n counts the dilution steps, not the tubes.
10-fold series from a 1,000 µg/mL stock
Cₙ = 1,000 ÷ 10ⁿ; matches the tool’s default settings.
| Tube (n) | Dilution | Concentration (µg/mL) |
|---|---|---|
| 0 | 1:1 (stock) | 1000 |
| 1 | 1:10 | 100 |
| 2 | 1:100 | 10 |
| 3 | 1:1000 | 1 |
| 4 | 1:10000 | 0.1 |
| 5 | 1:100000 | 0.01 |
| 6 | 1:1000000 | 0.001 |